OBD1 throws a code 41?

Hello,

This is a stalls at idle problem which can cause this code as well

Code 41 = Ignition Control (EST / Bypass Circuit Problem)

This video can help you find a vacuum leak which can be the cause.

https://www.youtube.com/watch?v=LRKWV4Are5c

Also, you should service the IAC valve and throttle body which are normal service items.

https://www.2carpros.com/articles/idle-air-control-valve-service

and

https://www.2carpros.com/articles/throttle-actuator-service

Please go over these guides and get back to us. Please upload a short video in your response of the problem, so I can see what's going on. Ken

Ken,
Thanks so much for your response. To date, this is what we have accomplshed. After viewing your reply we removed the throttle body, cleaned and purged all of the ports. Replaced the IAC with new. We are in the process of checking for any vacuum leaks with a smoker. We also removed the 6 pin connector from the ICM and checked for voltage less than 1 volt an pin "C". Also ohmed out pin "C" (with power off of course) and verified an ohm reading of more than 200 ohms.
After clearing the error code, as soon as the car is started (runs normal, no irregular idle noted) the service engine light illuminates. After shutting down the engine and interogating the PCM, 4 flashes and 1 pause noted. If we allow the engine to warm up, the oscillating occurs at idle (Fluxs approximately 150 rpm).

Is the engine misfiring? I have seen the coil pack go out and cause this issue, but there are different types can you please upload an image of yours? Does it look like this? Check out the images (below). Please upload an image or a short video in your response, so I can see what's going on. Ken

Ken,
It does not misfire at all. We replaced the ICM about a month ago because of an ignition fuse that would blow. Once replaced, the engine ran great!!
Once again, the car starts up, runs, immediately the check engine light illuminates, throw the 41 code. When the engine warms up, the rpm ocscillates 100-150 rpm.

Did you install new spark plugs and plug wires? I know it doesn't misfire but if the voltage of the coils is too high it will create this code, also did you have this code before the ICM change out?

Ken, We we're able to solve the mystery. Found that the back plate for the Newly replaced ICU did not have the DC4 compound applied to protect against the heat generated by the engine block. That explains why, when at operating temperature, the fluxuating RPM would occur. We replaced the ICU, after applying the thermal barrier compound, no more code or check engine light!

NICE!! Glad you could get it fixed, thanks for letting us know. Please use 2CarPros anytime we are here to help.