My 95 SSEI began shifting rough and has a noticable miss when I rev the engine. My transmission went out and was replaced last week, and I still have the roughness while driving at highway speeds. Yesterday it started making a popping noise under the hood. I investigated and found that the popping noise was at the post where the number one spark plug wire connects to the first of the three ignition coils. I replaced the ignition coil (1 of 3), and the popping stopped. However, the engine still had a miss when reving, and within a minute, began running very rough. Too rough to drive. I put the orignal ignition coil back on- the popping started again, but the car is driveable with a little roughness during some shift points, and a noticeable miss when the engine is reved. Any ideas what I should try next? I might have to replace all three coils. I just had the transmission changed, but this problem was going about two weeks before the transmission was replaced

Have you pulled any codes from the PCM :?:

Does this happen when the engine is cold or all the time?

First off, welcome to the club!

I suppose the first question to ask is...do you have a check engine light on? If not, then it has to be something simple...like a vac leak, or really fouled plugs.

There could be any number of things wrong with the motor. If your plugs and vac lines are all ok, lets start with the simple things first.

It'* running rough, right? So let'* unplug the MAF sensor, then start the car. If it doesn't start, plug it back in, then unplug it when its running. Does it smooth out? If it does, the MAF is either dirty or bad. If the problem continues, or actually quits running...the MAF is probably still good. Plug it back in and move to the next sensor...TPS.

TPS sensor tells the PCM what the throttle position is. If it isn't working, the PCM will try to figure it out on its own based on MAF readings and RPM. Unplugging the TPS defaults the value to "0", which is the value needed for idle. Unplug it, and if idle smooths out, then that sensor is suspect. If not, plug it back in, and move to the next possible issue. Note that this only works for idle tests. The TPS is also needed to determine shift points. Since you said your shifts are "rough", this may indicate a problem in the sensor that might not be there at idle. Keep this in mind...but in order to be sure, a scantool will tell you in a hearbeat or two.

Fuel pressure...you will have to hook up a gage to the rear of the fuel rail to get the reading. Should be 40-45 at idle, around 50 under a load (e-brake on, car in gear, and high idle). Lower numbers indicate pump is on its way out or the regulator is dying. If all that is good, then...

ICM...that this the plate underneath the coils. Make sure that plate is CLEAN and zero corrosion between it and the aluminum pedestal it sits on, as that is the grounding point for it, as well as the heat sink (it makes ALOT of heat). Autozone should be able to test it for you on the bench IIRC, just to see if it is bad. Take a gander at techinfo on how to measure the coil resistance while you have those things off.

That'* quite a bit to check, but if you have all the tools, this can be done in under 30 mins start to finish (except for testing the ICM that is). BTW, what plugs are you running? Bosch platinums are majorly bad juju for these motors.

Here'* a link to the Techinfo article mentioned above.
http://www.bonnevilleclub.com/forum/...e=article&k=33

Thanks for the information. I dont have all the tools I need to start checking these possible problem areas, I will have to wait until I can get into a buddies garage. I will post whatever results and remedies that I find. thanks again

Thanks for the information. I had only a small repair to make. My plug wires were bad. One of them had somehow been cut.