380SL Rough Running

[kbrooks]

I have a '81 380SL that will usually start great when cold, but you have to let it idle a bit prior to driving or it will die soon as you put it into gear. If it dies (cold), you have to hold the starter 3-5 seconds before it will start again. When cold, the car will lug a bit if you try to accelerate too much. As it warms up the car begins to miss badly and within a few minutes it will die when you come to a stop. You can immediately restart it and it will run. Funny thing is, it will start and idle when hot and you can rev it up while in Park and think nothing is wrong. Soon as you put it in drive, it misses and lugs and will die repeatedly. I've replaced cap, plugs, rotor and wires and most of the vacuum couplings. The problem started with the cold idle/power issue and progressively worsened and now you cannot drive it at all. Any ideas??

[ctaylor738]

There are lots of posts on these sorts of problems, as you will discover if you do a Search.

But it sounds to me like you have warm-up regulator trouble (cold running problem), and possibly a vacuum leak. As a first step, put a gauge on it and check control pressure and system pressure. Then get a manifold vacuum reading at warm idle. Also, use your Mityvac to see if both sides of the WUR hold vacuum.

[kbrooks]

I appreciate the response. I did look through the posts but did not see one that exactly matched the problem I'm having. I had a 450 once that had a WUR problem. It would start and run perfectly until warm, then it would die and would not restart until completely cold. Because of this, I was thinking of the idle controller.. Anyway, I'll try the solutions you suggest.. maybe I'll get lucky. Thanks a bunch!

[ctaylor738]

The idle controller is easy to check. Pull the connectors to the valve back enough to get the pins of your meter on the connectors. You should see 3-4.5 DC volts.

On an 81, you can also pull the connector off the temp sensor at the right rear of the engine and bridge the contacts (warm engine). You should see an increase in RPM's to like 900 because the idle controller thinks the engine is cold. This will tell you if the controller's little brain is alive.

[kbrooks]

There is 12v on the terminals for the idle air valve when car is cold (disconnected electrically but physically installed). I removed the valve. It is open regardless of voltage applied. It does click when energized, but remains fully open.