Hi all. I have a 2000 Bonneville SLE with the 3800 II engine. The car is missing badly. At idle, it doesn't miss too bad, but when you put it into gear and give it some gas, its just terrible. I replaced the spark plugs, and wires with AC/Delco units, and checked the PCV valve, and vacuum lines. They all seem fine. The car also has what I would almost describe as a "knock" down by the harmonic balancer when gunning the gas with the car in park and sitting still. Would a bad harmonic balancer cause these symptoms?

Thanks for any help.

Forgot to mention the 'service engine soon' light flashes if you get the RPM'* above around 2000. The code reader only picks up a P0300 'random misfire' code. Thanks again.

,Please post a video of the engine. When it'* running give it a couple quick revs and allow it to go back to idle between each.

is that one of the cars that can have the magnet for the cps come loose and rattle around in the timing cover?

Those were the Series 1 and earlier motor. He'* got a Series II. I've never seen one come apart..but heck..anything is possible right? From his description..I'm thinking he spun a bearing.

Thanks for the replies everyone. I will have a video taken, and post it as soon as possible. In the mean time, the car was taken to a local shop, who put it on a scanner. They said that cylinders 2 and 5 are the ones misfiring, and they tell me the cause is the ignition control module. They said compression in the cylinders is good, but the module is pretty much done. This is the only shop I have around me, but I trust you guys more. Would you say the module would cause these problems? I can get a brand new module for $365.00, or a used one from a scrap yard for $50. I can't afford the brand new, so I will have to go to the scrap yard, but I have bought many, many things from this yard, and they always treat me right. But, back to the question, do you guys think this could be the problem? As for the 'knock' sound, they said with the engine misfiring so badly, it was causing this sound. Does this sound reasonable?

Thanks again for your replies.

sounds like a coil is failing. The problem you described is often tied to a cylinder misfire. The cause is typically a bad plug or wire. Since you have replaced them, a coil is all that is left. I had the problem, and it ended up simply being corrosion on one of the coil contacts. Corrosion on the coil contacts is super easy to check. Just pull the plug wire and make sure the coil post is shiny.

The only thing I can't figure out, if it is a coil, is that it should be tied to a specific cylinder, not a random misfire.

i dont understand why one scanner would say something different, you can swap coils and see if the problem moves to the other cylinders

Aren't cylinders 2 and 5 on the same coil? I think they are but I'm not sure. If they are, switch the coil for cylinders 2/5 with another coil, and scan to see if the misfire moves to the other cylinders. If it does, replace the coil. If not, it could very well by the ICM. Pick one up at a JY.

By the way, plugs, wires, coils and ICM are not the only things that can cause single cylinder and multiple cylinder misfires. A bad fuel injector can cause a single cylinder misfire. A failing fuel pump can cause multiple cylinder misfires. There are also a number of mechanical issues that can cause misfires. The only way to find out is to be able to check the engine when it is actually misfiring to see if all cylinders are getting spark or not. If one or more cylinders are not getting spark you can focus on plugs, wires, coils and ICM. If all cylinders are getting spark you likely have a fuel problem and should start with injectors and fuel pump. Injectors can be checked by listening to them to see if they are actuating, and using a noid light to see if they are getting signal. Fuel pump can be checked by checking fuel pressure at the schraeder valve on the fuel rail.

LIke I said, start with switching the coils. The fact both cylinders misfiring are on the same coil make it the prime suspect.

Changed the coils around, and took another look at the plugs and wires to make sure they were all seated properly, and there was no change. Shop also said fuel pressure was good, so I decided to call a local junk yard, and try an ignition control module. He had an almost new ICM with three almost new coils on it for $50 (Canadian). Seeing how the ICM'* are well over $200, and everything else seemed fine, I decided to give it a go. Swapped it out, started the car, and she runs like a million bucks. No misfire detectible by ears, eyes, or the code reader.
I would like to say a HUGE THANK YOU to each and every person who chimed in on this thread. You people are the best, and without you, my car would be sitting for a very long time. Keep up the good work guys and gals, and once again I thank you so much for your time and help.