My brother has a 92 SE. It just started running very rough. He said it runs just fine in park and neutral, maybe just a little rough, but once he puts it in gear it studders and runs very rough, particualrly from 49-52 mph. He has cleaned his plugs, two were pretty fouled, and bought a new ignition coil and swapped it around. None of that has helped. I told him to get trouble codes (the SES has not come on), check the resistance of the plug wires, and possibly disconnect the battery to reset the computer. He doesn't think it is tranny related, he got a rebuilt one a whle back.

Any ideas?

I have even missed this one. The two plugs that are towards the firewall and forward on the engine tend to run exceptionally hot. This can lead to carbon tracking on the ceramic portion of the plug. This will look just like a black hairline crack of the plug. This, under load becomes an easier path to ground than jumping that gap of the plug itself resulting in a miss. Last time this happened to me (more than once) I pulled one of the plugs and found the tracking and changed in along with the wire. It was still doing it but not quite as bad. Turned out the one next to it was tracked as well. Tell your bro to have a look, it only takes a couple of minutes.

He cleaned them pretty good, and it is still happening.

After I told him to check the resistence of the wires, he found a bad wire that led to a bad plug. Problem fixed.

I've found that when you have one bad plug or wire, the car starts having problems around 50mph.