ZZtop

Recently my car has had a very rough idle, with stumbling that you can feel in the shifter. It seams to be outside temperature dependent, not motor temp. If it is cold out, like at night (45degrees), it idles better (not completely smooth) then when it is hot out(70degrees). This has been there ever since I installed my new waterpump and opti spark, both Genuine GM parts, about three weeks ago. I believe that it is neither of those two parts, but possibly something affected when doing the install. It could also be something completely unrelated to the install.

Today, I was talking to a friend after just firing up the car and it was ideling for a good long while. We heard the air pump click off and a few seconds later the car went crazy: the car was reving up and down between 500 and 1500 RPM and it got so rich it almost hurt your eyes. I turned off the car, started it back up and it did its normal stumble/rough idle. We let is sit there for a long time and it never went crazy again. This was the first time it had ever done this. It does feel low on power too, especially off idle.

If there are any sensors I can meter, anything i can check, clean, etc. let me know. I do not have a scanner or access to one, I know that would help a lot and I am working on that. Thanks a bunch fellas.

Things new on the car:
-GM Opti spark
-GM waterpump
-GM opti spark harness
-plug wires a few months ago

shoebox

Since you did work on the front of the engine, maybe you did something to the temp sensor in the water pump or even the IAT. Info for testing the sensors can be found on my Tech Page, but monitoring with a scan tool is the easiest. Sometimes the sensors may give bad readings in certain temperature ranges.

terlox

Check for wire rub throughs.

What about your coils?

ZZtop

I will try to get a DVM and check everything tomorrow. Do I check the sensors with the key in the on position, motor running, or car off? Where should I measure the temperature from to reference to the resistance table?

shoebox

Measure voltage to the sensors with the key ON and plug disconnected from the sensor. Measure the sensors with connector unplugged (you are just reading resistance). If engine is cold, sensors will read close to ambient temp. If hot, you might compare to the dash gauge for the coolant temp. The IAT will be a little harder to judge.