Quote Originally Posted by nvestysly View Post
I drove the vehicle for the first time in several weeks. The ECM remains temporarily moved away from any moisture that might drip from the air conditioning ducts. In total I drove about 50 miles today. I did not use the A/C today because the outside temperature & humidity were quite pleasant.

About 20 miles into the stop & go traffic and errands I was running I was idling at a traffic light. The car surged and I could hear the IAC counts must have increased dramatically because the sucking sound under the hood. Fortunately my foot was firmly on the brake pedal so the car didn't move much before I stepped even harder on the brake to keep it from lunging forward and hitting the car in front of me. As I said, this thing has a mind of it's own.

As I was getting close to the end of my 50 mile round trip the check engine light came on. Arggh. The engine became sluggish because it was back to base timing without any advance. I knew from past experience that if I turned off the ignition and restarted the engine the CEL would turn off and the timing would be back to normal. So when I was coasting down a hill I did just that - turned off the key for a moment and then turned it back on - and the timing went back to normal.

So here's my latest question/issue:

The idle speed on the engine is not consistent. When I go through the entire process of setting the throttle plates, the engine idle, TPS voltage, the IAC closed, and get it tuned in with the engine idling and in gear (I have a powerglide) it seems to be fine for a few minutes. If I rev the engine and let it come back to idle it doesn't return to the idle speed that I set previously. Sometimes it's higher and sometimes it's lower RPM. I'm thinking this variation in idle speed and corresponding variation in TPS voltage might be causing a problem. In particular if the idle goes a little low it seems like the ECM may try to compensate and open the IAC to bring the idle up to the set point. But this may not be the right TPS voltage because the throttle plates aren't where their supposed to be. Okay, I'm going around in circles again but this dang thing has me baffled. Why does it run fine for a period of time then go a bit crazy?

Some helpful information on the position of the throttle plates - It appears the throttle plate screw will not control the actual position of the butterflies on a consistent basis. One time I set the parameters and the next time I drive the car those parameters are off kilter. It's as if the throttle plates are not returning to the same position each time. There doesn't seem to be any slop/wiggle in the throttle shaft. What should I look at to investigate this further?

1project2many indicated I should try to follow the stalling/hard start issue and I'd like to do that but it seems to have gone away for now. I plan to drive the vehicle several times in the upcoming week so I'll keep an eye on that issue too.
Something to try is to disconnect the throttle cable and manually flick the throttle to verify it is returning to the same place every time. If it doesn't, your throttle body is binding. If it looks good, start thinking about your throttle cable. It should be parallel to the manifold and at about the same height as the throttle connector on the throttle body. With it disconnected, tug on it to see if it feels sticky.