I just installed a new GM crate motor using all my TPI stuff and now my car revs at 2500 RPM's. I checked for vaccum leaks and do not see any. I also set the TPSsensor. I even tried turning the idle screw until the butterflys close enough to hit the wall of the throttle body and it still revs high. what could this be. What does a motor rely on for idle speed on start up. Does the motor need the TPS and IAC sensors when you first start the motor and let it run for a few minutes? what is causing my motor to run so high for. please help I need to set my timing and fuel pressure and cant do it until i get the motor to idle right first.

 

is the IAC installed? if so did u set it correctly? i think there is a tech article here on how to do it, also it resets its self after u drive like 40 MPH or somethign like that,

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

 

I took it off and measured the distance and it was fine.

 

wut about after it warms up?

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

 

same thing the motor never revs down i let it warm up to aboyut 220 degrees. I even unplugged the TPS sensor and the motor just keeps revving st that RPM

 

what year is the TPI system?

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

 

1991 speed density setup. all i need to know is what controls the motor idle speed. I need to check anf fix this tomorrow. i need all possibilities

 

idle speed is controlled by the IAC valve, which opens and closes to control the amount of air needed. The speed density system uses a MAP sensor to know the amount of engine vacum, which if u have low vacum could also cause the engine to run high. the IAC is pretty much all the controls idle, at least all i can think of now, u might wanna try disconnecting that whenever u work on ur car.

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

 

so are you saying that my MAP sensor may be bad. Also does the motor use the computer and sensors when it starts up and is cold. You know like in closed ans open loop mode.

 

i doubt the MAP sensor is bad, it would probably throw a code, but u might have a vacum leak, do u have a vacum gauge.

But to answer ur other question, yes the computer used the IAC when in open loop mode (warm up mode) to control idle speed. in fact it always uses the IAC as soon as you let off the gas. once the engine is warmed up, then it starts taking info from the O2 sensor and other sensors.

i hope i am helping you some..

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

 

i do not have a vaccum gauge right now but what should the reading be if i get one. yes you are helping me a lot. it just seems like no matter what i check i just cant seem to get this fixed. i wil try again in the morning thank you very much i will also recheck the post in the morning to

 

vacum should be maybe around 18 +- 3 or so. i don't remember exactly.

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

 

by chance did you remember to go into dionostic mode and made sure the iac is completly closed then unpluged it when you set the min air?

 

i have not set it yet. i just took it out and inspected it.

 

you definately have a vacuum leak somewhere. id go back and make sure you have the clamp to the rubber intake on the throttle body good. go back and give all of your runner bolts a snug test just to be sure. try getting a piece of hollow rubber tube and place one end of it at your ear and move the other end around the intake, this will make vacuum leak hissing noises much more apparent.