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Discussion Starter · #1 ·
Yess I have a 2003 hyundai tiburon gt 2.7 v6 I started putting premium fuel in it after the Rebuild and I've started having trouble with it Revving on its own and then it falls flat on its face untill it catches up....I've Changed the Throttle position sensor, idle air control Valve also and it's still doing it...it also has a Cold air intake....any help would be apriciated....
 

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Premium fuel is a waste of money unless you are boosted or have significantly advanced your ignition timing. Go back to regular fuel because your OEM tune is designed for it. Flame propagation is different on premium and you can actually lose power from using it on a tune designed for less octane.

What was all involved in your rebuild? Did you replace sensors after the rebuild with genuine Hyundai sensors? If not, stop where you are and source the right sensors. This is especially important for MAF, TPS, CPS, CAS and O2 sensors. Our ECM does NOT play well with "OE" parts store garbage.

Look for vacuum leaks. Most common cause for weird idle and it's free to diagnose yourself. Otherwise check to see if you mixed up your IACV and TPS connectors. They are identical except for their difference in color.

A dirty or failing MAF or IACV is another common cause. Clean your MAF and ensure it is a genuine Hyundai or Siemens branded MAF.

An incorrectly seated or failing TPS could be another cause. Hook up an OBD2 scanner and monitor you TPS, with key on engine off, pressing it slowly to the floor. You should see a range of about 5% to 80% smoothly increasing as you press it to the floor.
 

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Premium fuel is a waste of money unless you are boosted or have significantly advanced your ignition timing. Go back to regular fuel because your OEM tune is designed for it. Flame propagation is different on premium and you can actually lose power from using it on a tune designed for less octane.

What was all involved in your rebuild? Did you replace sensors after the rebuild with genuine Hyundai sensors? If not, stop where you are and source the right sensors. This is especially important for MAF, TPS, CPS, CAS and O2 sensors. Our ECM does NOT play well with "OE" parts store garbage.

Look for vacuum leaks. Most common cause for weird idle and it's free to diagnose yourself. Otherwise check to see if you mixed up your IACV and TPS connectors. They are identical except for their difference in color.

A dirty or failing MAF or IACV is another common cause. Clean your MAF and ensure it is a genuine Hyundai or Siemens branded MAF.

An incorrectly seated or failing TPS could be another cause. Hook up an OBD2 scanner and monitor you TPS, with key on engine off, pressing it slowly to the floor. You should see a range of about 5% to 80% smoothly increasing as you press it to the floor.
Agreed....to add on, codes are great but may take a bit to set.
Also, common issue when removing the upper intake (UIM) is to get a mounting bracket between the throttle body and UIM. Thus a huge post MAF airleak.
 

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Discussion Starter · #4 ·
Premium fuel is a waste of money unless you are boosted or have significantly advanced your ignition timing. Go back to regular fuel because your OEM tune is designed for it. Flame propagation is different on premium and you can actually lose power from using it on a tune designed for less octane.

What was all involved in your rebuild? Did you replace sensors after the rebuild with genuine Hyundai sensors? If not, stop where you are and source the right sensors. This is especially important for MAF, TPS, CPS, CAS and O2 sensors. Our ECM does NOT play well with "OE" parts store garbage.

Look for vacuum leaks. Most common cause for weird idle and it's free to diagnose yourself. Otherwise check to see if you mixed up your IACV and TPS connectors. They are identical except for their difference in color.

A dirty or failing MAF or IACV is another common cause. Clean your MAF and ensure it is a genuine Hyundai or Siemens branded MAF.

An incorrectly seated or failing TPS could be another cause. Hook up an OBD2 scanner and monitor you TPS, with key on engine off, pressing it slowly to the floor. You should see a range of about 5% to 80% smoothly increasing as you press it to the floor.
Thank you Sir, I've had thoughts on the premium Fuel, my thoughts were that it's Richer and Burns different from unleaded all I wanted to do was treat my Baby to some Good Fuel :( guess I'll go back to That, And yes I just replaced the IACV this Morning and yes I always go back with genuine hyundai parts..and my rebuild was Timing Belt, Pullies, and was put back with Gates, and all gaskets and seals when I put the motor back in.... and Yess I know about the "Compatible" But it's "Not Compatible" parts I bought a Cps sensor off amazon and it said compatible with my motor just wasn't to my computer, lol just replaced the Fuel pump assembly Unit, and then the sensors I had from a Donor I swapped them out and it still did it....I just put the Brand new IACV this morning it still did it... So my Thoughts can only Be It's The Premium Fuel....
 

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Premium fuel will not cause this problem. Period. Neither will regular grade unleaded.

You say you've already replaced the TPS and IAC with genuine Hyundai parts so it shouldn't be those. Look for a binding throttle or cruise control cable, or take the throttle body off and clean it up really well. Sometimes they can stick and cause erratic idle/revving.
 

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I didn't mean to insinuate that premium fuel may be causing you problems. Your car will run fine with premium and it will not cause weird idling problems. It's just a waste of money because all it has is more resistance to pre-detonation but one of the side effects is a different flame propagation speed. That is all.

As Charlie recommends, check your throttle body to upper manifold for a vacuum leak. The bracket that holds your EVAP purge valve can sometimes get sandwiched between there and causes a vacuum leak. Make sure it's on the outside of the throttle body rather than between the TB and upper intake manifold.

Would you mind sharing a link to the parts you purchased so we can help verify if they were indeed genuine Hyundai components? Just because Amazon claims the part is "compatible" doesn't necessarily mean it was a genuine Hyundai component or that it was OEM quality. I find counterfeits and false advertising on all corners of the market whether it's eBay or Amazon... For example, MOSTPLUS sells a MAF for around $20 but there is a genuine Hyundai MAF that sells for around $170 that is hard to locate because Amazon's search algorithms are skewed and seem to favor the lesser expensive items. That MOSTPLUS MAF is straight garbage and causes more problems than it solves. Unfortunately this is the case with many other sensors and components you may find on Amazon. It's to the point that Hyundai/KIA have started marking their components and packaging with holographic stickers to help buyers identify what is genuine and what is garbage.
 

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Discussion Starter · #7 ·
So I have litterly Done everything To It, I just changed the upper and lower intake gasket today and put a Brand new MAF sensor, The only thing that I haven't changed is the fuel pressure Regulator, It's to the point now when I got out to start it I have to hold the gas completely on the floor while it cranks for over 20secs Then when it starts it holds an idle at like 4000 to 5000 and even when I hit the gas it won't revv down It stays revved up until you put it in Gear and release on the Clutch then it lowers the revving some what.....plz Help
 

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Yess I have a 2003 hyundai tiburon gt 2.7 v6 I started putting premium fuel in it after the Rebuild and I've started having trouble with it Revving on its own and then it falls flat on its face untill it catches up....I've Changed the Throttle position sensor, idle air control Valve also and it's still doing it...it also has a Cold air intake....any help would be apriciated....
Are you sure you don't have a vacuum leak?
 

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Discussion Starter · #9 ·
Are you sure you don't have a vacuum leak?
Yess So I've went thru and changed Everything trying to fix my Revving issues, And Changed the one last part And it was the Evap Purge Valve, Never thought this would make it do what it Did, I Changed everything Before This one it was 52$ at AutoZone But It Hasn't Revved Since I changed it, I think it Fixed my Problem, I know I seen alot of people having the same issue so Try that......
 
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