HELP - 1988 Grand Am revving at 3000 rpm's

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Hi, I hope someone can help. I changed the motor in my 88 grand am quad 4 dual overhead cam and now when you start it it runs at 3000 rpm's and I can't lower it. The motor I replaced it with is a 91 dual overhead cam 2.3. I changed the air flow sensor, throttle body positioning sensor but I used the thottle body from the 88 quad 4. The motor runs fine except for the high rev. There is no vacuum leaks. I am wondering if the fuel rail system has more fuel pressure from the 88 compared to the 91. It seems to be getting more fuel than required when you put your hand over the throttle body to try and starve it for air it still doesn't idle down. I don't know what to think because I was told by GM that this 91 is the same motor except I had to use all the sensors and throttle body off my 88. If anybody can help diagnose this problem it would be greatly appreciated. NOTE: I did not change the sensor for timing and it's not running rich or lean.

posted by  dlvinet

well, you just answered one of your own questions...if it's not running rich, then the "fuel rail system" doesn't have "more fuel pressure from the 88 compared to the 91". Too much fuel wouldn't cause that anyway...unless you're getting additional air from somewhere, which brings me to my main point...

Your problem sounds like one of two're IAC (idle air control motor/solenoid) could be bad, did you use the same IAC off of the 88? If not, that would be the first place to look...I had a similar problem on my t-bird when I converted to an H.O. motor, but found it to be the IAC. The other thing to look for is that the throttle cable isn't being pulled on somewhere along the line, possibly holding the throttle blade open slightly. Try disconnecting the throttle cable to see if the idle speed drops down to where it should be. If you do both of those things and nothing works, let me know.

posted by  Sick88Tbird

Hi there, I changed the IAC and the throttle cable is not even hooked up. The throttle body is completely closed. Any other ideas?

posted by  dlvinet

are you positive there are no vacuum leaks at all? it is possible that a vacuum leak at the throttle body/IAC/intake could cause a high idle, even the slightest of leaks will cause such a problem. Look for hair-line cracks along the intake manifold, the throttle body, etc. Is the check engine light coming on? If so, check the codes.

posted by  Sick88Tbird

yea i have the same motor with the same problem and i changed these two sensors and it still does it. Plus my header is getting beat read too at idal so i think where both in the same boat. I've checked for vacume leaks but nothing has come up. Hope someone can help use. thanks

posted by  greandam_boy123

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