Originally Posted by sublettd

I chased a similar problem for approximately two years and it was solved last weekend. The round plate on the throttle body was bent and out of adjustment. (Most likely caused when the engine backfired a couple years ago.) Simply, the engine was getting too much air at low idle, causing it to run rich and idle poorly.

We replaced the round plate on the throttle body with one from old throttle body with the same part number that was lying around and the engine is now purring like a kitten. Just have a little anti-freeze mixing in with the oil after we put the engine back together. Front cover is coming off to look for a busted/leaking o-ring--but that is another story.

The plate has to be centered with a very fine clearance around the edge and, if I recall correctly the height of the plate should line up in the center of the 1mm ridge at the bottom of the opening on the throttle body. The adjustment for this in the SL (107) is a detente under where the fuel line comes into the right front of the fuel distributor as you face it. You can't get to the adjustment without removing the throttle body.

There was one other adjustment that was made after we pulled the throttle body and fuel distributor off. It was at the front of the engine where the rubber piece the throttle body sits on fastens to on the manifold. There was no spec for this that my mechanic could find, so he made a (very well) educated guess in his adjustment.

You may not have a bent plate, but it could just be enough out of tolerance to be allowing too much air into the intake at low idle.

Hope this helps.