Try to locate the ICM on a GM Cavalier 3.1L/V6 MFI Station Wagen 1991

Under the dash, on the firewall or the side panel, behind the glovebox, and to the right a bit. Look for a silvery box about the size that computer software usually comes in.

Thanks Pete,

You mean the ICM is inside the car, not in the engine apartment?

BTW, do you think that it is a reasonable assuption that my problem is related to the ICM? The car has about 125K miles on the clock and still has the original factory ICM module.

The car just has a new TCC solenoid put in, and it seems that the solenoid takes care of the problem that engine stalls after highway drive.

John

I believe that Pete was thinking of the ECM (engine control module). The ICM (ignition control module) is underneath the three coil packs which on a 3.1 liter V-6 are mounted to the lower front side of the engine. Just follow the sparkplug wires down... Not easy to get to.

There is no reason to assume anything, diagnostic routines are developed for the specific purpose of avoiding assumptions and guessing.

Your original description of the problem is kind of vague.

Neil,

Thanks for the help, let me start all over again.

The problem started yesterday (TCC solenoid was changed a day before and no driving after that), in the morning, start the car and drive for 35 miles without any problem on highway. After stopping to drop off passangers for about 30 seconds while the gear is in "N", then drive for about 200 yds to park the car, before pull into the parking spot, step on the brake to make the turn, car stalled. I cann't remember exactly if the gear is in "N" or "D". Restart the engine without any problem, proceede to park the car.

3 hours later, start the car and drive for about 3 miles with no abnormality, proceede to park by reversing into the parking spot, this time as soon as the car stopped and the gear was put in "N", the engine stalled. Again, restart the car and reverse into the parking spot just like a normal car.

Another 3 hours later, start the car and did the following drive:

1). 10 miles on a 35 mph stretch; 2). 25 miles on a 55 mph highway; 3). 6 miles on a 39 mph city street;

then pull into drive way to park, as soon as the car came into a full stop and the gears were put into "N" (on its way to "P", but not yet since I try to see what will happen) and the engine stalled again.

This car had the similar problem about a year ago, i.e., stall for no reason while waiting for traffic lights, it happened a few times (definitely less than 10 times) during that time, and everything seems fine since then (it never happen again untile now).

This time, the stalling frequency is too high, something needs to be done to fix the problem.

After discussing the symptom with a person who has replace a number of ICM, have reach the conclusion that it is highly unlikely that the problem is caused by a fualt ICM, since the car drive normally each time before and after the stall (if ICM is bad, then the car should behave badly each time before and soon after the engine stall.).

I am running out of options, please help.

Thanks.

John

There are a number of things that I would check out first; Power steering pressure switch Park neutral switch Idle Air Control Valve Power brake booster (for vacuum leaks) Check for vacuum leaks Check base idle speed/clean throttle body

You're correct in that since the engine seems to run fine otherwise (no missing or stumbling) that the root cuase is likely not to be the ignition module, however, in 1991, GM was sending out batches of ECMs with cold solder joints, so at the very bottom of the suspect list is the ECM ( engine control module).

Neil,

Thanks again for your kindly help.

Now I am have somd difficulty to locate those items mentioned in your above post, I have a Hayns manual, but most of the items are not listed in the book.

1). Power steering pressure switch I presume that this switch is located somewhere in the steering column, is it inside the engine apartment or inside the passanger apartment?

2). Park neutral switch

I assume this switch is somewhere undernearth the gear shifter, on top of the tranny?

3). Idle Air Control Valve

This is the item I have not found yet, and is the more likely cause of my problem. It is not on top of the main air intake housing, I take it that it is either on the side, or on the bottom of the air intake housing. Do I have to disassebly the intake housing in order to get access to the IAC valve?

4). Power brake booster (for vacuum leaks)

Soap water check?

Hope to hear from you soon.

John

Power steering pressure switch, if it has one, will be on one of the power steering lines under the hood.

The park/neutral switch will be on the transmission, underneath where the shift linkage connects. I doubt that's the problem though.

The IAC valve is in the throttle body, it should have a 4-wire connector on it, probably held in by two Torx screws.

My pleasure.

In the power steering pressure line between the pump and he steering rack, basically, it tells the ECM that there is an increased load on the engine when the powere steering is active.

Where the shift lever enters the transaxle, it tells the ECM whether the vehicle is in gear or not so that the idle strategy can anticipate the extra load imposed by the torque convertor.

Bolts to the throttle body near where the throttle linkage/cables connect, held on by two Torx head screws, it's the only device attached to the throttle body that has four wires going to it.

Pinch off the vacuum hose that supplies it, listen for any change in how the engine sounds or runs.