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I have seen issues with the throttle cable/cruise cable either too tight, or getting stuck in the sleeve. If the cables are adjusted correctly, try a bit of silicone spray on the cable.

Also, ive seen MANY worn out throttle bodies or potentially damaged throttle bodies.

So two things happen here both specifically to v6 tiburons and other hyundais.

First, ive seen bad engine mounts allow the engine to move enough where an aggressive shift or throttle demand will allow the engine to rock back. The first part to contact the firewall is the nut on the shaft to the throttle body. If hit hard enough, the shaft can bend slightly and cause the throttle plate to stick.

Second, Ive seen throttle bodies worn out where there is side to side play in the throttle plate. When it gets bad, the side of the throttle plate will contact the housing and stick.

In both cases, the rpms can stick around 3000 or more. A throttle blip will usually get it unstuck, but daily driving can be annoying.
 

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Discussion Starter #82
I appreciate the thorough response.

I have seen issues with the throttle cable/cruise cable either too tight, or getting stuck in the sleeve. If the cables are adjusted correctly, try a bit of silicone spray on the cable.
Well, I did do a custom routing for the throttle cable. But the RPMs don't stay constant, they very regularly get to about 1.5-1.7K then dip to 1.1-1.2K then back again, consistently, for some period of time, where in most cases eventually it stops doing that and lands and stays at 1100RPM. This is all while in neutral, pressing brake, not touching throttle. So because it's a consistent fluctuation I would think it's somehow electronically-related, as opposed to an analog cable.

Also, ive seen MANY worn out throttle bodies or potentially damaged throttle bodies.
Yeah, I have the NGM 70TB, but it is in really good condition so I wouldn't think that's the issue. As a last resort I'll put the stock UIM + TB back on to test.

First, ive seen bad engine mounts allow the engine to move enough where an aggressive shift or throttle demand will allow the engine to rock back. The first part to contact the firewall is the nut on the shaft to the throttle body. If hit hard enough, the shaft can bend slightly and cause the throttle plate to stick.
Ehh, I have solid NGM mounts front & rear lol. My engine isn't moving in the slightest.
 

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ok, if the TB is good, double check that cable. If all clear there, id probably be hunting a vacuum leak. I generally use brake cleaner for testing. Every once in a while, ill have to watch fuel/air values on a scanner to find the leak.

Oh, you mentioned something about using new gaskets. If you didnt, start there first. Peace of mind.
 

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Oh, you mentioned something about using new gaskets. If you didnt, start there first. Peace of mind.
Yeah, yesterday I sandblasted & painted the spare LIM I have, and will use it plus new gaskets to rule that out.

I found a trick to get it to not fluctuate idle: When coming to a stop (either via coasting or pressing brake), as long as I leave it in gear and wait until the RPMs get below 1500 and then pull the shifter out of gear (i.e. not press in the clutch) it'll stay at 1100RPM idle, most of the time (maybe every time; only discovered this yesterday). Trying to figure out what that means though. It has me convinced it might not be a vac leak then, because, wouldn't the fluctuating idle then be constant?

Anyway. I'm gonna go to the auto wreckers tomorrow and see if I can find a spare IAC and brake booster hose. Rather do that instead of throwing a lot of money at new parts if I then find out those components didn't even need to be replaced.
 

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Yeah, driving today, it seems that every time so as long as engine is in vacuum (correct me if that's the false term - basically just not giving gas) and simply pull the shifter out of gear below 1500RPM (without use of clutch) when approaching a stop then it won't do its fluctuating idle and simply stay at 1100. Still, 1100 is high for idle, but isn't all bad.
 

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Yeah 1100 is still too high. Are you using the factory pcm? Actually, do you have access to a scanner to see air/fuel values? We really just need to see if you are super lean. That should tell you if you have a vac leak. I feel like your IAC probably isnt the issue here.
 

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Yeah 1100 is still too high. Are you using the factory pcm? Actually, do you have access to a scanner to see air/fuel values? We really just need to see if you are super lean. That should tell you if you have a vac leak. I feel like your IAC probably isnt the issue here.
Running lean? Now you've got me concerned..
By PCM do you mean ECU? If so, yes, it's an early '03 2-bit. I do have a Hydra that I planned on making use of for going to stage 2, but perhaps I should try it out this week.


Also noticed that I think my car is consuming more gas, but a bit early to tell. Granted I have been stepping on the pedal a bit more since it sounds amazing lol, and am often in a low gear since that is how things are in Toronto with painfully slow speed limits and a speed bump every 5 seconds. Car feels truly excellent on the highway though; incredibly stable with the coilovers, Michelin PS4S's & manual steering. Anyway, getting back on topic lol... so as for fuel I did install a 190LPH fuel pump, and with the poor gas mileage I have been getting I was assuming running rich, though this I believe could very well be the ECU correcting a lean condition, so you might be onto something. Running the stock ECU as far as I could tell though should be fine I thought; I am running stage 0 Sniper (so stock injectors), but I do also have the 70mm TB installed, which initially I thought might've been a risk for stage 0. I was thinking to work out any quirks on stage 0 first before moving to stage 2. But come to think of it... I feel like my car isn't any faster at the moment than it was pre-SC (so I/H/E), so perhaps it is possible I am maxing out the stock injectors. Hmm... But one last point to consider is I have a smaller underdrive crank pulley installed. So my Sniper should be hardly generating any boost (but under pressing the gas pedal hard you can hear the whine). I was gonna use the stock crank pulley but the serpentine belt I have would be too small for it (due to my custom setup lol...).

Sorry for so many words, there's a lot of factors to consider at the moment :/

I do have access to a scanner, I'll see what it reads.
 

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Somehow, your supercharger slipped my mind. And yes, PCM = ECU. Same thing.

So lets remember what a supercharger is... forced induction. By nature, you are stuffing more air into the cylinders. If you are on a stock ECU, you are absolutely going lean, and the computer is attempting to compensate. This absolutely will increase gas consumption.

But, we're focused on the idle atm. I know that some people had issues with cable length after installing the s/c manifolds. I would double check and make sure you have slight slack in the cable.

Also, check your reading on the throttle position sensor. Its possible the throttle body isnt adjusted correctly. Since its aftermarket, the throttle plate might have some adjustment like on the plate or even an idle screw.
 

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Somehow, your supercharger slipped my mind. And yes, PCM = ECU. Same thing.

So lets remember what a supercharger is... forced induction. By nature, you are stuffing more air into the cylinders. If you are on a stock ECU, you are absolutely going lean, and the computer is attempting to compensate. This absolutely will increase gas consumption.
True. I am monitoring it, and it's seemingly not too out of whack. I have the OEM fuel consumption gauge (part of the multi-gauges) in my car and it's behaving fairly similar to what I remember driving my car last, i.e. from a few years ago so memory is not perfect on this lol.

As for SC though, I do have the smaller UD crank pulley. And my car performance-wise feels the same as it did pre-SC, so that smaller pulley is probably significantly reducing boost on the already low boost on stage 0.

Plus, if I was running lean I'd be getting a lean code wouldn't I? Currently only have codes for high idle and speed sensor. Granted, I have anti-foulers on the secondary O2's, so that may throw things off.

But, we're focused on the idle atm. I know that some people had issues with cable length after installing the s/c manifolds. I would double check and make sure you have slight slack in the cable.
True, but I did ensure it had a tiny bit of slack upon install. Still, I'll see what I can do there.

Also, check your reading on the throttle position sensor. Its possible the throttle body isnt adjusted correctly. Since its aftermarket, the throttle plate might have some adjustment like on the plate or even an idle screw.
Yeah good point. I mean at this point I actually have two stock TBs + 3 extra TB gaskets. I could very well pop on a stock one and see if that makes any difference.

For what it's worth I picked up an extra brake booster hose today from the wreckers. Came out of an I4 model but I get the feel it'd work. So I'll start with that.
 

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True. I am monitoring it, and it's seemingly not too out of whack. I have the OEM fuel consumption gauge (part of the multi-gauges) in my car and it's behaving fairly similar to what I remember driving my car last, i.e. from a few years ago so memory is not perfect on this lol.

As for SC though, I do have the smaller UD crank pulley. And my car performance-wise feels the same as it did pre-SC, so that smaller pulley is probably significantly reducing boost on the already low boost on stage 0.

Plus, if I was running lean I'd be getting a lean code wouldn't I? Currently only have codes for high idle and speed sensor. Granted, I have anti-foulers on the secondary O2's, so that may throw things off.



True, but I did ensure it had a tiny bit of slack upon install. Still, I'll see what I can do there.



Yeah good point. I mean at this point I actually have two stock TBs + 3 extra TB gaskets. I could very well pop on a stock one and see if that makes any difference.

For what it's worth I picked up an extra brake booster hose today from the wreckers. Came out of an I4 model but I get the feel it'd work. So I'll start with that.
Ah, so couple things here. I wouldnt rely too heavily on those multi gauges. For example, while the vehicle is running, voltage will always show around 14v. However, the alternator doesnt charge all the time. If you use a volt meter plugged into power, or anything else to watch actual vehicle voltage, you'll see the system drop to ~12v while driving, but the gauge stays at 14v. They do this so people dont constantly think theres something wrong with their charging system. Kinda the same reason GM stopped using actual oil pressure gauges, and other manufacturers for that matter. A lot of people would be surprised to know that some vehicles will drop all the way to 10 psi of oil pressure while idling after the engine is hot. So, who knows what shenanigans they are using to measure fuel consumption and vehicle torque o_O

As far as the lean code, sometimes the ecu wont show it because of a different problem. codes kind of take priority order in some circumstances. Sometimes you have to fix one code in order to discover a different one. The secondary O2s are purely emissions related, so no worries there. They arent the problem. But definitely start with what you know. Get your speed sensor sorted out first.

Something easy to do is disconnect cruise control completely, and give the throttle cable extra slack and see if the idle problem still exists. Of course, dont leave it like that. We simply want to rule out a cable issue. If the problem still exists, readjust and move on to the next thing.

Something else you can try is to stick your finger over the bypass hole in the throttle body while its running. If you actually have a nasty vacuum leak, the engine will stay running. If not, it should stall. But before you remove the throttle body, Id still try to take a look at the values on a scanner or some sort.
 

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Ah, so couple things here. I wouldnt rely too heavily on those multi gauges. For example, while the vehicle is running, voltage will always show around 14v. However, the alternator doesnt charge all the time. If you use a volt meter plugged into power, or anything else to watch actual vehicle voltage, you'll see the system drop to ~12v while driving, but the gauge stays at 14v. They do this so people dont constantly think theres something wrong with their charging system. Kinda the same reason GM stopped using actual oil pressure gauges, and other manufacturers for that matter. A lot of people would be surprised to know that some vehicles will drop all the way to 10 psi of oil pressure while idling after the engine is hot. So, who knows what shenanigans they are using to measure fuel consumption and vehicle torque o_O

As far as the lean code, sometimes the ecu wont show it because of a different problem. codes kind of take priority order in some circumstances. Sometimes you have to fix one code in order to discover a different one. The secondary O2s are purely emissions related, so no worries there. They arent the problem. But definitely start with what you know. Get your speed sensor sorted out first.

Something easy to do is disconnect cruise control completely, and give the throttle cable extra slack and see if the idle problem still exists. Of course, dont leave it like that. We simply want to rule out a cable issue. If the problem still exists, readjust and move on to the next thing.

Something else you can try is to stick your finger over the bypass hole in the throttle body while its running. If you actually have a nasty vacuum leak, the engine will stay running. If not, it should stall. But before you remove the throttle body, Id still try to take a look at the values on a scanner or some sort.
Ah, now that is interesting to know.

Yeah so here is where I stand now, with some progress!
This morning when I was at a wreckers I picked up a brake booster hose from an I4 model, and speed sensors from an ABS-equipped V6 model (however I am suspicious it may have had the incorrect sensor installed at some point - I'll find out this week). So turns out the I4's hose is shorter than the V6's, but that's to my advantage because it happens to be a good length for the Sniper + 70mm TB .setup I have. Man, I should have known: my previous brake booster hose had some cracks (manufactured 2002) - surely a vac leak there. I just replaced that hose and drove home now and the car overall feels better. As does the brake pedal of course (weirdly, previously with the cracked hose it was actually incredibly easy to press the brake pedal - but not in the same way as if air was in the lines. I much prefer it now being slightly more firm. So while this didn't fix the idle issue it still helped other odd RPM behaviours otherwise. Also noticed that my fuel consumption gauge was now more gradual (previously a little jumpy), and overall lower fuel consumption by the looks of it. I feel like that leak could be the most significant factor to poor mileage. I will find out, it just so happens I filled up on tonight's ride home as well.

Now, as for the scan tool. Well, first I'll mention: previously I stated I can avoid the car fluctuating RPMs so as long as I pull it out of gear below 1500RPM. That's true, but just as well while I am at a stop I can shift into 1st, hold brake, and release clutch slightly until it stops i.e. when clutch starts to catch and I'm effectively halfway stalling the engine. This has a 100% success rate. Ok, so previously I noticed the scan tool mentions when the "Idle Switch" is On or Off. I noticed that every time it's fluctuating it was Off, and every time I could get it to stop it would be On (now it's late in the night after a long day so I may have the On/Off reversed here lol but the point is it switched at these points). So, with that in mind, I do believe my issue might be the IAC after all. Or perhaps its wires. I will inspect those if need be.
 

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Ok couple more things.

So does your brake pedal feel similar to when the vehicle is off? A stiff brake pedal is usually a symptom of a bad brake booster.... which just so happens to be vacuum assisted and also difficult to detect with the brake cleaner trick. When the diaphragm goes bad, it causes an internal vacuum leak. You can test this by pulling the booster hose off the manifold while the engine is surging, and stick your finger over the port to block vacuum. If the engine stops surging and idle comes down properly, you've found your problem.

Im not ruling it out, but I dont believe the issue is your IAC at the moment. If the motor starts to surge, its essentially trying to do its job. As the motor idles high, it closes the IAC to bring the idle down. It ends up being too much, and it opens again... causing the idle to go up. This is the surging condition. Basically the IAC is actively trying to control an out of control idle, usually due to a vacuum leak.

Get the vehicle warmed up. Use your scanner to check short and long term fuel trims.
Need to know both bank 1 and 2. What is the long term value, and eyeball an average short term value. Values should be similar on both banks as well. If one bank is drastically different, let me know that too.
 

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Ok couple more things.

So does your brake pedal feel similar to when the vehicle is off? A stiff brake pedal is usually a symptom of a bad brake booster.... which just so happens to be vacuum assisted and also difficult to detect with the brake cleaner trick. When the diaphragm goes bad, it causes an internal vacuum leak. You can test this by pulling the booster hose off the manifold while the engine is surging, and stick your finger over the port to block vacuum. If the engine stops surging and idle comes down properly, you've found your problem.

Im not ruling it out, but I dont believe the issue is your IAC at the moment. If the motor starts to surge, its essentially trying to do its job. As the motor idles high, it closes the IAC to bring the idle down. It ends up being too much, and it opens again... causing the idle to go up. This is the surging condition. Basically the IAC is actively trying to control an out of control idle, usually due to a vacuum leak.

Get the vehicle warmed up. Use your scanner to check short and long term fuel trims.
Need to know both bank 1 and 2. What is the long term value, and eyeball an average short term value. Values should be similar on both banks as well. If one bank is drastically different, let me know that too.
Sorry, maybe I wasn't quite clear (was late in the night lol) but my brake pedal is not stiff. Now it's normal, lol. Previously, weirdly, it was too easy to press. The difference isn't that significant, but in any case it feels better. I do recall at one point (when I had the cracked vac hose on), while at idling at 1500RPM if I were to pump my brakes then the RPMs would raise to ~2000RPM temporarily. Just throwing that out there for anyone reading this to understand if they'd happen to have the same issue as I had.

Hmm, ok, I will let you know the values. I recall seeing the values and pretty sure they were normal but it's been many years since I have last dealt with fuel trims so my familiarity with them has slightly diminished since :/

Aside from that: I have been monitoring my fuel consumption it is noticeably better so far. My idle issue is also somewhat less frequent, but it's still there, and still always idling at a solid 1150RPM according to scanner lol. Haven't had a chance yet to replace LIM + gaskets, but I should have time for that hopefully tonight.
 

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Sorry, maybe I wasn't quite clear (was late in the night lol) but my brake pedal is not stiff. Now it's normal, lol. Previously, weirdly, it was too easy to press. The difference isn't that significant, but in any case it feels better. I do recall at one point (when I had the cracked vac hose on), while at idling at 1500RPM if I were to pump my brakes then the RPMs would raise to ~2000RPM temporarily. Just throwing that out there for anyone reading this to understand if they'd happen to have the same issue as I had.

Hmm, ok, I will let you know the values. I recall seeing the values and pretty sure they were normal but it's been many years since I have last dealt with fuel trims so my familiarity with them has slightly diminished since :/

Aside from that: I have been monitoring my fuel consumption it is noticeably better so far. My idle issue is also somewhat less frequent, but it's still there, and still always idling at a solid 1150RPM according to scanner lol. Haven't had a chance yet to replace LIM + gaskets, but I should have time for that hopefully tonight.
Well, basically we're looking for values to be close to 0. You can have some slack around -10 and 10. outside of that, and we're getting into code territory. but if you watch your values and spray around the intake and vacuum areas, you'll see the short term values spike if there is a leak
 

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Well, basically we're looking for values to be close to 0. You can have some slack around -10 and 10. outside of that, and we're getting into code territory. but if you watch your values and spray around the intake and vacuum areas, you'll see the short term values spike if there is a leak
Yesterday I grabbed the scanner and drove home on the highway. When I first started up the car while idling the ST values were ranging from about 0 to 14 or so, often in the middle of that range. The LTFTs at this point were 4.1 & 4.2 for each bank (it has been one week since ECU was reset; 300km driven). Then started driving and occasionally glanced at the ST values while driving. In general, B1's values were often higher than B2's, but not always - often B2 would overtake. But overall, B1 was slightly higher. I also got both banks to hit negative values (unsure what this means really). I took photos of the scan tool which might help:




You can see the LT values increased to >5 in that drive. And weirdly, B1 reduced to <4 at some point.
 

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Trims tell what the ECU is doing with fuel amount.
Positive numbers means it's adding fuel (richining).
Negative numbers means it's reducing fuel (leaning).

Yes, best is "0" LTFT's....decent is within 5, acceptable is within 10.
Also, you really want the trims close.....not a 8 and a -8..... yes, 8 is OK, but they're 16 points apart...

STFT's can jump all over as you change load and throttle.
 
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Discussion Starter #97 (Edited)
Ahh, received a new CEL last night: P0449. Still have the original EVAP canister on my car, so might as well order some parts lol. Two years ago, when Ontario still did emissions tests, I almost didn't pass because the EVAP monitor wouldn't get ready even after a 1000km of driving or so. So this has been failing for some time (but granted I drove my car for only a few months of the last two years).

Edit: I recall my EVAP and fuel lines are also extremely rusty, so I am sure that's part of the issue. I planned on restoring the rear of my car this winter anyway, so I guess I'll deal with everything then. Only driving this car for another month this year anyway.
 

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yeah, short term trims will be erratic while driving. We want to look at the short term while idling at operating temp
 

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Well, after over 335000KM my EVAP canister finally failed. Had the best time filling up the car last night at an ultra slow pace lol. I have never over-filled my tank and I have owned by car since it had 193000KM on it. Must've failed just a couple days ago. I do wonder if it's related to a new issue I experienced then which was a hesitation, like misfiring, when going at a constant rate around 2-3K RPM. It felt like an ignition or MAF issue based on previous experience. But I do now wonder if it could be fuel related due to a failing EVAP system in some way.

Oh well, guess it's another trip to the auto wreckers for me lol
 

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Theres a lot to unpack there mechanically. Technically everything you listed can cause those symptoms.

Im sure you are on top of it already, but for anybody else reading this... I cant stress this enough: start with what you know is 100% broken whether you think it might be related or not.
 
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