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I did a search, and couldn't find what I was looking for, and decided to post.
A good friend has a base '94 automatic, that has a rough idle. The problem is that when in park or neutral, it is fine. When placed into 'gear' is when it surges or dies. The following parts have been replaced, TPS, IAC, Mass air flow sensor, MAP sensor, and egr valve, injectors, and fuel pressure regulator. No check engine light.
It only does this when at operating temperature, so it's fine when engine is cold.
I did a search, and couldn't find what I was looking for, and decided to post.
A good friend has a base '94 automatic, that has a rough idle. The problem is that when in park or neutral, it is fine. When placed into 'gear' is when it surges or dies. The following parts have been replaced, TPS, IAC, Mass air flow sensor, MAP sensor, and egr valve, injectors, and fuel pressure regulator. No check engine light.
It only does this when at operating temperature, so it's fine when engine is cold.
Since no codes are thrown and it's just a 'rough idle', rather than throw parts at it randomly, let's use data. Connect a computer, and log data from the car as it drives along. Chances are the culprit will make itself obvious in the logs. That's what I would do if I had a 94-95...and it's what I do do.
As suggested, I purchased the OBD2-to-USB cable and downloaded the Scan9495 software.
Now we have data to look at, please see screenshots below, as well as the *.cvs files containing the 06/04/2023 data.
It appears that the data is all over the place for every sensor/actuator, i.e. it is all junk.
The screen shots of Excel plots are from data collected on or about 05/02/2023, the screenshot of the Scan9495 is from data collected on 06/04/2023.
Notice that the PCM believes that the the car is going 200+MPH on several occasions even though it never moved an inch, only putting in PARK/DRIVE/REVERSE/NEUTRAL.
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1994 Idle Problem
