380SE sounds like missing on 1 cyl - how to test?
 

The problem appeared about a week ago, when it idled great until a restart outside the mall. Ever since it's developed a loping, rough idle, shaking the car when it is sitting idling. It seems to smooth out when in gear and driving normally, but to me it still feels rough.
I read up on what to look for and have a pair of motor mounts on order, but no real gut feel that they are the problem either. What I'd like to try is pulling the plug wires one by one to try and isolate which cylinder may be missing. But I'm afraid of electrical shock from the motor running while I do this, and the plug wires are really hard to get off the plugs.
How would it work if I shut it down and removed the wire ends, one by one, from the distributor instead of the plug, then start it up to check the effect?

When we had a plugged injector, I found results inconclusive when pulling plug wires. Like you, I worried about shock, so only did it with the engine off. What worked was disabling the ignition, running the starter, then pulling plugs to sniff for fuel. Even that I repeated several times before deciding I smelled gas most of the time on all but #1, and never on that one. That was the bad injector.

With our 4, there was a definite loss of power and sluggish acceleration in addition to the lumpy idle. Maybe with the 8 not so noticeable.

Steve

So I shouldn't have any problems with disconnecting at either end of the plug wire, engine off, then fire it up?

What I did was pull the plug connector. I then plugged a spare sparkplug to the end and arranged it against engine ground. This allowed me to verify spark AND prevent damage to the coil from excess HV generation. This would be more of a pain to do if disconnecting at the distributor. In addition, you might risk arc-over to another plugwire, which could confuse the issue and start a carbon path somewhere. On ours, I also find it easier to pull a plug connector than those tenacious boots on the distributor cap.

Steve

Thanks, that's the caution I was anticipating....the last thing I need now is to make the situation worse by screwing up the electronics. I'll try your method, since I think I should pull the plugs anyway to see if there's fouling (although I put fresh ones in last year, less than 2000 miles ago).

OK, do I feel stupid or what....took the air cleaner off to start my search for leaking vacuum lines, fuel injector seals, and ultimately a bad wire or plug boot...right on top of the valley area under the air cleaner, there was a vacuum line popped off the steel tube. I plugged it back in and voila, back to a smooth idle again! Appreciate the help sbourg, and it may come in handy again. Right now, I'm back on the 'love' side of the love/hate relationship with this car. Wish they were all that simple to fix!