Hello to everyone.
From few weeks ago, we notice the car was giving intermitent pulls when hard acceleration, and then became doing it rarely when cruising normally. SES Light was on too. The dealer checked it and changed the O2 sensors. But intermitent acceleration was still there. The problem got worse this weekend, when I was using the car and the SES light start flashing (misfire) The car was on parking, so I just waited until It stoped. Then the rest of the day the car worked on 5 cilinders or less. And the idle was horrible too. On sunday we replaced the sparkplugs with AC Delco Iridium Replacements, and the idle is good now. But still missfires when accelerated. SES light is off.

Our only other options are the coil packs or wires. Maybe another sensor. My dad is going to get it to a mechanic tomorow, but maybe there is something we can check before we have to pay some otherone to doit :(

Sound like a plug wire and I'm going to say #6 (its hot in that corner by the cross over).
Check your plug wires with a multimeter and inspect your coil posts for corrosion.
If a coil is toast it takes out two cylinders so I dont suspect that.

How did the plugs look when you pulled them out? I'm guessing wires here as well.

Thanks. Something less to check. Could be the wires. My dad told me that it had a little intermitency on idle, runs good when pushed gently, but misfires when accelerated. I'll keep you informed

The plugs didn't looked so bad. None of them were wet. The tip looked a bit worn, and looks like it was running a little rich because of the faulty oxigen sensors. But nothing out of this world :?

I have similar problem with my SC '01 with 40k miles. When I first got it, got bad machine-gun type misfire intermittantly only when pulling grade in OD. Replaced plugs with Bosch Platinums. Problem disappeared for about 2 months. Then started intermittant very slight misfire only when idling, either hot or cold, but NEVER UNDER ANY LOAD. Replaced plug wires. Misfire cleared up for about 30 days. Ran 750 interstate miles fully loaded, 4 passengers; all kinds of mountains. No problems. Three days on the road and very slight misfiring only at idle reared its ugly head again. Was so bad that check engine light set once but cleared up, not to return after about 50 highway miles.

Okay, maybe its fuel injector related. Ran can of strong fuel injector cleaner through her. Took about 3 days to clear up perfectly.Thought I had it fixed! This lasted for about 3 weeks. Yesterday morning she ran fine to and from work. In evening I took her out and she was misfiring worse than ever, mostly at idle and "some" at cruise speed. After about 40 miles it totally cleared up and has been fine all of today. I ran another can of fuel injector through her just for the hell of it, but I am really stumped on this one.

Anyone else have this problem?..... and what the hell is the cure?

Interesting , very curious if either of you can feel the misfires through the gas pedal at all. I just had this problem.

First changed out the Platinum plugs I put in couple months earlier, than saw far amount of corriosion on the coil packs and inside of spark blug boot on coil side. The closest to the engine was worst was less rust the farther away, #1 was still shiney. I also only have 34K.

Ricky5.0L I'd bet yours is the wires and/or coil pack corrosion.

compyelc4 dobut that'* the problem with you, check maybe for a loose connection on a boot or coil pack? maybe you got an injector on it'* way out. Find someone with an Atap and get the car scaned.

compyelc4, yours too sounds like an ignition problem. Even new out the box plug wires can be bad?

The car was too shaky like to feel any vibration on the gas pedal But the tach did vibrate when the misfire occurs.

I told my dad to check up the coil packs for corrosion. But right now the island is on hurricanne warning and the bonnie has been taken for a safe place to pass the storm. Also I study 100 miles away from my home, so I only see the car on weekends and don't use it very often. And right now I cant go home until the storm passes the island, and that could be tomorow morning. But I'll keep you informed on whatever we found.

Thanks for the help

Comp, if you have platinum plugs in your car right now, even though they're only 2 months old or so, that could be part of your problem.

Both of these problems do sound like ignition problems. Ricky, the #6 wire is the typical suspect, but the rear bank in general is normally more abused by heat as well. Check them first with an ohmmeter, then make sure they're not shorting out anywhere. (spray a light mist of water on the wires at night....you'll see any shorts).