I have a built motor 12,000 miles with a 16g hahn turbo.......just the other day, I started the car and it went up to 6000rpms.....shut it off....waited a few.....started it back up and it keeps doing it.....any thoughts what it may be? thanx

You have a vacuum leak. Make sure all the hoses are connected to your intake manifold, and your throttle plate is fully closed for starters.

Blow smoke over the motor while it is running and see where it goes in to the intake manifold.. that will be where your leak is.

Originally posted by adamzty
You have a vacuum leak. Make sure all the hoses are connected to your intake manifold, and your throttle plate is fully closed for starters. Blow smoke over the motor while it is running and see where it goes in to the intake manifold.. that will be where your leak is.

shaaazaam. x2. i agree.

so it wouldnt be the IAC or map sensor at all?

Prob not. I had the exact same issue when I installed a new TB and overtighted one of the bolts. The resulting vaccum leak caused it to idle extremely high. Torqued bolts correctly, problem solved

yea but why all of the sudden after driving it a year would it decide to do this? bolts were torqued to spec

anyone? cant find a vacuum leak anywhere.....anywhere else i can check?

I'd say possible IAC sticking open. or throttle plate itself sticking open although I'm sure you've checked that already right?

ok so i changed the IAC, still high....changed the map sensor, still high.....checked the TB bolts and also still high......when you start the car, the idle RPM's go up to 5000 like if you were stepping on the gas when starting the car. hope that helps a little better

does it stay at 5000 rpms? It's possible the throttle position sensor may be bad. if there's no vacuum leaks and IAC is good. worst case scenario may be leaking fuel injectors causing the IAC to correct for additional fuel but the TPS can cause that too. do you have a check engine light?

fuel injectors arent leaking....i was just one of the sudden things when you go start your car and you like WTF happened now? yea, you start the car and it immediately goes straight to 5000 and stays. check engine light is off. cant get the car to run to have a light stay on. havent changed the TPS but will do that if it could be an issue.

it's the only other thing i can think of unless there may be a problem with the wiring harness.

ill check it tuesday and if that doesnt work ill be back here......what wiring harness could be bad?

I doubt the harness would be it. You wasted you cash on the Idle Air Control Valve cause 9 times outta 10, when those suckers go bad, it won't run. Gotta keep your foot on the gas to keep it running. Check you intake gaskets. I had issues with my lower intake gasket having pieces missing and causing the car sit at a higher rpm.

actually I've had IACs stick fully open and cause that concern. the IAC doesn't necessarily have to be shorted it could just be stuck open due to carbon build up among other things. but checking the intake gaskets is another good idea. if it's still the factory gaskets they get very brittle in high mileage cars and tend to start coming apart. also check the harness to the IAC and TPS. make sure there's no obvious bare wires or wires melted together.

ok so i changed all the sensors on the intake mani: IAT, MAP, TPS, IAC......still does it.......not sure where to go next. Car has 12000 miles on a new motor, hahn 16g setup, egr block off.....i was driving down the road last week and the rpms just spiked up to 5000 while i was driving.....checked the fuel pressure and it was at 45-48psi......any possible way i might have a stuck open injector or something of the sort?

You have a huge vacuum leak. I would check again and again. Another idea would be to check out your intake manifold gaskets.

ok so it happened while you were driving. that makes a big difference. I'm willing to bet you blew part of intake gaskets out under boost. first, did you ever replace the intake gasket when you installed the turbo system? now it does sound like you have a pretty nice sized vacuum leak. get some carb cleaner, start the car and spray it around where the intake manifold meets the head. if the idle jumps up further then you need an intake gasket.

Originally posted by kballard81
any possible way i might have a stuck open injector or something of the sort?

That will not cause the RPMs to increase.

Unplug the TPS and start it up. See what happens..

the gaskets on the intake and plenum are new.....when i built the motor a year ago, i put all new gaskets and seals and machine work into the motor. I cleaned all the sensors and put them back on and tried a few extra ones that i have laying around in the garage that i know are working. so the car had 1500 miles on it before i hooked up the actuator to the turbo and now it sits at an even 12,000 miles. I unplugged the TPS started the car and same thing. high rpms. i cant find a vacuum leak anywhere. the only thing i havent checked is the canister. any ideas now?

ok......i changed the computer with a brand new OEM one and still nothing, but heres something new, car goes up to 5-6K and stays steady, then if i tap the gas, it will go back down to 2K and then when it hits 2K it will start to climb again until i tap the gas again. Anyone?

Do a "smoke test" If it is in fact a big vacuum leak it should help. Start the car and blow smoke (like from a cigg) into the engine bay. See where it is getting sucked into the engine. My bet is its either the TB gasket or IM gasket.

Thanks everyone for your help.....The Intake Mani gasket was gone and so were half the bolts.....Not sure if they fell out under boost or what what they were gone. Appreciate everyones help.

must have been sealing for a moment under throttle.

Figured the intake gasket was the case. I had changed one and used a light film of regular RTV and lost parts of my gasket within a year. I used Copper RTV and have no problems since then.

Hazard - I never said it wasn't possible. I just said 9 times outta 10 it won't run not that it would spike the idle from sticking open.

yeah i agree with you. it is rather rare but i have seen it in the past. I'm surprised i didn't think about the intake gasket sooner.