I have owned a bunch of Pontiacs, but this is my first Bonneville. I recently purchased a 1991 Bonneville LE for use as a second car. It was cheap, and seemed to be in decent shape. I have a few general questions, however, and I hoped maybe some folks would have some thoughts.

The car has about 125,000 miles on it; when I got it home, I had a shop do some general work on it -- new plugs, LOF, new fuel filter, flush and fill radiator, etc. before driving it daily. Seemed to be OK at first. But then...

1. When cold, the engine runs very smooth, but as it warms up (10-15 min or so), it will skip. At idle, if the hood is up for observation, for example, it will run very smooth, then skip once or twice, idle smoothly, then skip again. This continues until the engine finally stalls. It will easily restart. The shop (a dealer with whom I have done a good bit of business) said the wires were likely bad, and that the fuel system (injectors/throttle) needed cleaning due to heavy carbon buildup. They have made those repairs, but still have not totally solved the problem -- which they admit. Since the car is a second vehicle, it is still at the shop and they are trying to track down the problem.

2. The transmission seems to pull very well -- on hills, no slippage, etc. The dealer suggeseted a flush and new filter. I haven't done this, because transmissions seem so finicky -- if it isn't broke, don't fix it, so to speak. Would you recommend the service, or should I leave well enough alone?

Any advice/suggestions would be greatly appreciated. Thanks!

The heat is making me lean towards a bad coil or two....or a bad ICM. All of these parts can be taken from a newer generation and used on yours. Do you know someone with another 3800 that you could 'trade' parts with for a few minutes?

Thanks... Unfortunately, I don't know anyone with that engine. What is an ICM and is it (or the coil) an expensive repair?

The ICM is the ignition control Module, it sits under the coils and tells them when to fire. I'd have to check my book to see which one you have for sure. I won't be able to do that for another hour or so.

Get it hot, then check for spark. If you're missing randomly, change the icm/coils. If it'* consistently one or 2 wires/plugs, change the wires or that coil.

After that I'd try replacing the Idle Air Control Valve. I've replaced my coil and module ('90 SSE) about every 2 years, and I changed out the IAC twice. Other thing thing about our cars are the alternator bites.


Welcome to the club

I don't know if they have done a scan or not; yes, I had the plugs replaced and other general maintenance. I would hope they did a scan; wouldn't that make sense?

When I first got the car, the thermostat was stuck open, so the engine ran rather cool -- very little heat. And it seemed to run fine. But I noticed when I got stuck in traffic or parking areas and the engine temp would rise a bit, the engine would just occasionally skip. When I would start moving, you could feel it occasionally miss at highway speeds. But at a red light, the skips would randomly hit, and, if severe enough, the engine would die. It would start right back up.

One night, I opened the hood and let it idle. I watched it. It was as smooth as glass for a few minutes, and then you could see/hear a skip. Then smooth for 30-45 sec. Then another skip and so forth, until the skips became worse, and then, finally, the engine just stopped and made a hissing noise as it ejected some air. Naturally, it started right back up.

After the thermostat was replaced, the skips became more problematic, since the car would heat properly.

So far, the dealer has only said they thought it was bad wires and that there was carbon buildup/tracking, so I needed to have the fuel system service to clean all that junk out. But apparently that didn't solve the problem, and it is still in the shop.

When it isn't skipping, it has substantial power, doesn't seem to burn any oil, has good compression, and runs very smooth, whether at idle or highway speeds.

Hopefully, I will know more tomorrow...

Thanks for everyone'* input.
Pete

Don't go to the bank on this, but judging by your more detailed description (excellent troubleshooting and writeup, I might add) I'd bet more on the Coil/ICM game. It'll be interesting to see what the final repair will be.

Fuel injectors and the fuel itself aren't normally affected by heat. Electronics are. I've had a coil go bad before, and it was heat-effected. This is very difficult for a dealership to diagnose.

COIL/CM has got my vote as well.

Thanks for everyone'* input -- I will keep you posted. So far, no news from the dealer, other than that he'* trying to get an ECM (said it was the same as an ICM?) to try out to see if it solves the problem.

Other than that, he said he could shoot the car. :?