I have a 87 TPI in my 1962 Chevy Nova. I put this system together from many parts. The intake, plentum, runners, fuel rails etc are off a 85. All the sensors and ECM are from a 87 Camero 5.7 with out the VATS. So really its a 87 system. The wire harness is Painless. The question I have is when I start the engine the idle comes up like it should it comes down to about 1000 rpm's then I will start to drive the car. If I dont stop and hold the engine back it will continue to idle until I do. What I mean is I have to pull up to a stop and hold the brake with the trans in drive until I do this it will continue to idle at 1000 until I do. I have replaced the IAC 3 times and have reset the idle. I am beginning to belive there might be something wrong with the ECM. Any help...?

Mitch

 

Sounds like it may not be entering closed loop. Have you verified closed loop operation?

 

It's going into closed loop.. I hooked my scanner up and verified that. Whats funny is you can sit and idle for about 5 min's and it will finally come back down. but if you drive it the idle will stay around 1000 and even thoe the ECM is calling for 550 or 600.

 

Well, if the ECM is commanding a 600 RPM idle, you have just ruled out a bad ECM.
When you pulled out the IAC motor, did you clean the bore it sits in and the idle passages? Also, since you say you pieced this system together from a couple years of parts, are you absolutely sure you have the correct gasket for your throttle body? There were 2 different styles depending on which years of TB you have.

 

When it does it look at the IAC counts and the TPS voltage to see if they are the same when it is idling at the correct speed. Also do you have a park/neutral switch and VSS input to the ECM.

 

I dont remember what year I purchased the gasket set for.. Would you think I should have the gasket for the 85 or the 87. The TB is off an 85..

Mitch

 

I do have a park/neutral switch and a VSS. I will take a look at the tps voltage and the iac counts.. What should the iac count be at an idle. I know the tps will be .5.

Mitch

 

Basically any positive IAC counts will indicate that the IAC is functioning. If you have 0 IAC counts then the minimum air was set incorrectly.

You should have used the gasket for the 85 throttle body, make sure you used the right one (most gasket kits contain both the old and new styles)

 

usually, the IAC counts on a properly functioning sys. will be 25-35, but anything above 0 and below the max(255?) will work

 

Check for vacuum leaks.