Hello and thanks in advance for any guidance in this issue.
We have a 1998 Firebird with 55,000 miles on it. Prior to a month ago it had never broke down or had any issues short of a battery and altenator a few years back. The only maintance we preformed over the years was oil/transmission fluid changes and injector cleanings.
The only modifications we made are cold air intake and flowmaster muffler and that was 3 years ago. It does use a K& N Filter and it is oiled/clean.
About a month ago we decided to put on new brakes, ironically as I was driving to my brothers workshop with the new pads the car broke down. First time ever breaking down and while on the way to do something to it really! It gave a computer code for cyn 3 misfire.
It would run but was misfiring quite alot. I remembered that feeling from a 95 camaro I used to have knowing it was probably a plug wire being burned by the manifold. I replaced the wires and plugs( and brakes!) And while before I got a computer error that said cyn 3 and would misfire at low throttle but went away at WOT now after new plugs and wires it was excellent and smooth low throttle and misfiring at WOT! Completely reversed.
The plug wires I was not sure on as they were a old but unused set so I went and got a autilite platnium set and put those on to be sure. I also replaced the fuel filter which had never been changed and cleaned the dirty K& N filter.
Now with all that done when it starts and decides it is going to be rough it seems to be that regardless if it is idle or throttled and just missing all around. However most of the time it doesn't misfire at all and is very smooth idle and running.
Over the last several weeks it has continued to do the very rough idle. Most of the time it is fine and runs great. When it decides to run bad it usually continues to do so until it is turned off. Sometimes it does it when it is cold, sometimes it does it after it warms up. Even though it feels like it is misfiring be it very rough idle about to die or in the driving range it does NOTgive a code anymore. I have not had a code since the day the initial cyn 3 misfire code and was cleared before the new plugs and wires.
What is making this hard for me to diagnose is how most of the time it starts/runs fine be it at idle/acceleration or even hitting the gas hard. Then out of the blue you go out and start it and it runs like it is about to die, sputters in acceleration and cannot be drove hard if hardly at all. We have been stuck out at places and had to drive home like that and other then the sputtering in acceleration it drives and makes it home just fine.
To give a idea in the 3+ weeks since it has had the stuff done, it is drove 4 times daily( start/drove to a place ) and this has happened only 3 times out of the probably 30-35 times it has been drove.
I'm really leaning towards either O2 sensors or ignition coils but other thoughts are welcome to explore. I really din't want to get into replacing thousands of dollars of stuff that didn't need it so hopefully you all can help!
Tuesday, June 26th, 2007 AT 3:31 PM