'99 olds. Alero 161000K 2.4L
my car started out just missing every now and then at around 45 mph. It began to get worse and miss when accelerating from a dead stop at idle. I found a few problems with the ignition system and ended up replacing the ignition coil housing, one of the ignition coils, spark plug boots, and spark plugs. Sometime after the first part replacement and the last the car began running terribly. I pulled the codes and thanks to OBDII I know that it has multiple cylinder misfire. At the time it really started running terribly (barely idling and vibrating at all engine rpms) I noticed wisps of smoke coming from the exhaust pipe (not a leak). This made me realize that the converter must be clogged, so I disconnected the pipe from the manifold and despite the noise the car seemed to run perfect.
next I busted up the converter insides and blew all the excess debris before reconnecting the converter to the muffler (it was connected to the exhaust manifold but not the muffler). Once I had everything hooked back up it ran perfect again for about two min. Then went right back to puttering and almost stalling at all engine rpms. I believed this to be caused by more debris from the converter that was still in the exhaust clogging the muffler. I just got a shop to replace the converter and asked if the muffler should also be replaced. The mechanic stated that in ten years he's never seen a muffler that needed to be replaced as a result of getting converter insides trapped in it.
at this point the car still runs like crap. I pulled the spark plugs and two were fouled. I bumped the muffler and could hear a fair amount of trash from the converter in it. My question is whether the most likely source of the random multiple misfire is the trash in the muffler or if I should check other parts for the cause of this problem.