So I picked up my car from the body shop yesterday, and it ran fine for a few miles. I got to a friends house, and noticed the idle changed, sounding like a dead cylinder. I shut it down, disconnect battery, let it sit a while, and it does the same thing. So i get it home, idling rough the whole time. Next morning go out to start to work on it, start it up, runs fine. I take it down the road, about a mile, and it starts to run rough again. Get it to a friends house, and start to pull plug wires, trying to verify which cylinder it is. I pulled the wire for the last plug on the passenger side head, and no change in engine sound. So I figured it was that one. I start to put the wire back on the cap, and with it arcing over that short distance, the motor starts to run better, but then goes back to being bad when i plug it fully on the cap. I haven't ever had a problem like this before on any car I've owned, so i am kinda stumped. Any ideas would be helpful. Its a 1993 sc400. Thanks.

 

did you check the ignition coils? looks like one side is going

 

If its arcing I don't think its the coil. I might try replacing the wire first. Sometimes the metal lead inside the wire that attaches to the top of the plug can break, when you moved the wire around it might have got a better connection, even though it was only on the top of the plug. If it's possible and you know anyone else with an sc400, trying taking the same plug wire off of theirs and try it on yours, see if it works. This way you won't have to buy one if you're not sure. If it isn't, then you have eliminated a factor keeping all others the same and you don't get confused. If it isn't the wire, try putting the old wire back on and replacing the plug. Good luck

Jon

 

unfortuantly dont know anyone local with a sc, or i would try swapping the wire.

Well i drove it to work today, about 5 miles, and it ran fine the whole way, took it out at lunch and it started to run crappy again. Talked to one of the other technicans at my job and he said to check the plugs, one could be fouled, pulled out that plug, and there was quite a bit more carbon build up on it than the others. Im gonna replace all of them and see what happens. They could have foulded from when my front o2 sensors went bad causing it to run richer. Im gonna trhow the plugs in later today and post up my results.