Guys, I am in one heck of a fix. I did a lot of work on my '85's engine and upgraded the ecm to the 165. Once I got the re-pinning done I fired the car up, it ran terrible and was pig rich. I thought I had messed up on the wiring. After 2 months ot tracing & cussing I checked my "new " distributor, it was faulty. I got another new one and installed it and that brings me up to what is happening now. My IAC valve sits on 160 counts all the time, if I rev it it may drop 15-20 counts but it will always come right back to 160. Also, the car will not go into closed loop no matter how long it runs. It hesitates badly when warm and won't idle at all when it is cold. Once it warms up to around 160* something kicks in and the idle smooths out & it will sit at around 800 rpm most of the time but will drop once in a while as it shakes a bit at the same time. I imagine I still have some wires crossed but have traced & traced and can't find a problem. I have a tune from pcmforless.
This may or may not have a bearing on things. I installed an Edelbrock Pro Flo XT manifold with a '98-'02 style LS throttle body, the IAC is a new Delco, also for the same years as the tb. The Chevy truck throttle body and IAC are different, should this be what I should be using?

 

The IAC valve does three things:

1 - Maintain idle speed. The ECM will step the IAC out if it thinks the idle speed is too low. This gets more air into the engine and the idle speed increases. The idle speed is calculated by the ECM based on the reading it gets from the CTS (Coolant Temperature Sensor) located on the front of the intake manifold under the throttle body.

Sounds like you have a problem between the CTS and the ECM. The CTS could be bad. If the connection is bad (or not there) then the CTS shows very low temperature. The ECM will be in "fast idle" mode, with the IAC valve stepped out. The CTS has to reach a certain threshold before the ECM will go into closed loop mode, which almost guarantees that this is your problem.

2 - Maintain AFR. After the ECM goes into closed loop mode it looks at the output of the O2 sensor and uses the injector pulse width to set the mixture. The IAC is used to fine tune the AFR.

3 - Throttle follower. The ECM opens the IAC when you mash on the gas pedal. The purpose of this is to keep the engine from stalling when you let off the gas and the throttle slams shut. Air flow goes from high to basically zero instantaneously so the extra air from the IAC keeps the engine running. The ECM backs off on the IAC as the car speed goes to zero so the idle won't be high when you finally stop.

 

Thanks, I'll check operation of the cts, it is brand new but that means nothing any more. I have to wonder though, when the engine is cold the cts would not be showing any temp anyway and when the engine is cold is when it is worse. I already know the yellow signal wire is in place and has continuity. Since all the black and black/white wires are ground would it make a difference if they were all in ground positions but maybe two were crossed? In other words say A1 wire is in A2 position and
A2 wire is in A1 position should they be okay since they are both grounds or should they be switched to work properly? I hope you can understand my poor description.

 

Your minimium throttle blade position may to to small, you may have to get you throttle open far enough for the IAC to work. Key on engine off ground the A to B diagonistic port and then disconnect the IAC. Turn key off, pull out jumper, start car use the throttle to keep it running and set the idle speed to 100 RPM lower then your desired idle. Turn car off hook up IAC now you should see some IAC counts that make sense.

 

Thanks, right at this moment it is running as sweet as can be but it is always worse when it is cold. I will see how it acts in a couple hours.

 

There are two types of grounds in the ECM.

One is the power ground and the other is the 5 volt reference ground that is used by some sensors.

The reference ground is connected to the CTS, MAT and TPS. It should go to pin D1 or D2 of the ECM (those two pins are connected together inside the ECM).

 

You will need to set the TPS when you get the IAC done.

 

Thanks to all of you, the problem was just a little of each of your suggestions tps, throttle opening, etc. It is running real smooth again. Now if spring would just hurry up,,,,,,,