I have a 1984 380SE that runs rough for 5 minutes when it is cold. It starts right up no problem, but when you put your foot into the throttle it sputters, backfires out the intake and can barely rev up. If it idles and warms up for 4-5 minutes it runs perfect and revs up strong with no hesitation. Is there a sensor that could be bad or something? Everything else is good just the first 4-5 minutes when it is cold it hardly wants to run. It is a 3.8l (116 engine) and 126 chasis.
Thank you for the help.

 

Mine had that same problem. It was the Overvoltage protection relay. It could also be the idle control valve or the computer. Does the car ever idle too high?

 

The idle seems to be fine. It never idles high but I think when it is first started the idle doesnt come up right away. I will have to check that. I havent been driving it because of this problem. How would I test the overvoltage relay? How would I test of set the idle control valve? I dont even want to think of what a computer is worth!
Thanx

 

The Over Voltage Protection Relay is in your fuse box under the hood. It is the only relay with the 10A fuse attached to the top of it. Pull the fuse with the car running and if the car has no idle change, that may be the problem. The only problem with the idle components in troubleshooting is, when the O.V.P goes bad, it shuts off many other components from working including the Idle control valve. You can check all the components the same way......pull the plug on the idle valve while the car is running. No change, could be the problem. Same with the Idle computer. The idle computer is the black box seated on the firewall under the hood. The OVP is pretty cheap. The idle control valve runs about 150.00, the Idle computer varies but you get it from a company that rebuilds them. Do some internet searching once you get it narrowed down. Ebay is another place to look. Good luck.