My 1991 Buick Park Avenue is throwing off code 41. I have replaced the cam sensor, knock sensor, and the ignition control modual under the coils pack. The car will work fine then the check engine light goes out and it starts to act up, mssfiring and sometimes shutting off. It usually starts back up but the misfiring continues. It only runs smooth when the check engine light is on. While driving the light will come on and off during the course of driving to the destination.

Question edited for clarity and typos.
Question moved from Misc to model category.

Camshaft magnets

https://www.google.com/search?q=1990+Buick+Park+Avenue+replace+cam+magnets

What you really need is a mobile auto electrician with a prograde scan tool computer to diagnose and test all the sensors.

Code 41

https://www.google.com/search?q=1990+Buick+Park+Avenue+code+41

Code 42

https://www.google.com/search?q=1990+Buick+Park+Avenue+code+42

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Replace your ignition module under your coil packs.

there is a little magnet inset in the camshaft gear that the camshaft sensor gets its signal from. this magnet, over a period of time, gets loose and falls out. the reason for the smooth running when the light is on is the ECM sets the ignition timing to base due to the loss of camshaft signal. to replace the magnet you will have to remove the timing cover to access the cam gear.

1991 Buick Park Avenue 3.8 liter V-6 VIN "L"

Identifying Ignition Types I and II
On Type I coil packs, three twin tower ignition coils are combined into a single coil pack unit.




On Type II coil packs, the coils can be replaced separately and the ignition wires are all on the same side of the coil pack.

With Type I Ignition




Hope this helps (remember to rate and comment this answer).

Crank sensor, ignition module under the coils these all would be good places to check. You might want to see if there are any codes.

Have you checked to see if you have voltage at the ignition coil and if the wiring between the coil and the ECM has continuity. There is always a possibility that one of the new components that you recently replaced could be defective. I have experienced this problem on more than one occasion.

Do you have power on the pink wire on the ignition module with the key on?

WHAT KIND OF CAR

I think you got your answer to the alarm issue. I had the same problem with rough idling, lack of power, and the chugging that occured when going up hill. I have a 1991 Park Avenue with 190k miles. Fixing the catalytic converter helped, but the real problem was in the ignition control module. It seems that older buicks will heat these units to the point that the glue inside melts and eventually exposes the electronics. Look for glue or exposed wires below the ignition coil. It's a $100 part that you should be able to change yourself. I hope that helps.

I had the same problem once, bought a new radiator pressure cap and it ended. Though the Code 41 doesn't play with that theory.

Look at this post for a 1990 Buick, scroll about halfway down the page or search for the word "code 41."