I just got done changing the head gaskets on the wife's 1999 Olds Cutlass. It runs and drives but... it has a pronounced vibration like one of the plugs are not firing. It's also getting an engine light that constantly flashes. All the push rods went back to the same place. I was told that the intake and exhaust push rods were slightly different lengths. I want to go out and start pulling wires off the coil packs but the wife wants family time. lol.

Does the car have an ignition system which uses one coil pack for 2 cylinders? These coil packs actually fire twice in one cycle..one fire being the real one, and the other is called a 'waste' fire. Maybe two cables to plugs replaced wrong way round?

It does have two plug wire connections per coil pack. The fireing sequence is correct. I fixed that earlier.

OK then...a stuck valve lifter, or a blocked oil way in a lifter? Is the oil pressure good?
New spark plugs...and gaps checked? New cables? (sorry..I am not familiar with the engine..just shootin' in the dark here...and therefore not saying you don't know what to check )

New plugs, wires and a cam sensor. I also had the heads decked and new valves seals put in. I hope it's not a lifter.

Just loosen the spark plug leads so they lie on top of the spark plug, start the engine, and then using a thick leather glove, and insulated pliers, lift each wire clear of the plug, one by one, so you can trace the misfire, and at the same time ensure there is a spark at each plug by holding the cable close enough to the plug to allow a spark to jump. In fact, by doing that, you can also tell if there is a faulty plug or cable too.
Is it consistently misfiring from idle to say, 2500 revs? or more? Is there any back-firing going on from the exhaust or intake? Have you got a bad injector? And one thing...cam sensors have a notoriety for being bad from new Try putting the old sensor back and see if things remain the same

Consistent miss and no back firing. I probably won't be able to look at it for another week because of my work schedual. It could be an injector. I had a hard time getting #2 and 5 to press in.

Can you get codes pulled?
If there was a cylinder not getting or only intermittently getting spark, you would feel a noticeable reduction in power, been there with a 97 cutlass.
If the check engine light is on, I would think that would be an indication of a fuel or ignition problem, not an internal failure.

It was cyl#3. I could hear a clicking from the fire wall side of the engine. When I pulled # 3 the spark hit my thumb, nice. The clicking / arching stopped. So I pulled the boot off the plug. The clip on the wire was bent out. I bent it back and pulled the plug. Somehow I got anti-seize compound on the end of the plug. I got it cleaned and reinstalled and the problem went away. Today I blead out the rest of the air.
The engine light went away after a couple of test drives as well.

Thanks for the help guys!

quote Originally posted by JetroGT: It was cyl#3. I could hear a clicking from the fire wall side of the engine. When I pulled # 3 the spark hit my thumb, nice. The clicking / arching stopped. So I pulled the boot off the plug. The clip on the wire was bent out. I bent it back and pulled the plug. Somehow I got anti-seize compound on the end of the plug. I got it cleaned and reinstalled and the problem went away. Today I blead out the rest of the air. The engine light went away after a couple of test drives as well. Thanks for the help guys!

Good find!