1996 Sl600 Surging At Idle.
 

Once it gets warm the car will idle in park from 1000rpm's up to 1500 rpms and back down then back up. it will just sit there and surge up and down constantly. The engine is still running smooth, but just hunting for the right idle. It isn't misfiring, and you don't really notice it near as bad if it is in gear. Just an anoying surge. No check engine light on either. give me ideas if you can. Thanks, Nate

Could be o2 sensor,could be pot. could be EHA,could be fuel mix? With high idle though I am going to lean toward air/fuel mix,Yet all of this needs to be working together.

I had a similar sounding problem on my 94 SL500. It turned out the be the throttle body assembly. (There was a code logged, but no enginer light.) They replaced it, but I believed after seeing the old one that a simple cleaning of the throttle plate would have done the trick.

Could be any or all of the above. My problem was deteriorating wiring insulation within the ETA and MAF harnesses. Once I fixed this, my surging was gone.

http://www.v12uberalles.com/MAF_rewire.htm
http://www.v12uberalles.com/throttle_actuator_rewire.htm

I was just at the dealer today and they had a S600 surging as well. It turned out to be the secondary fuel pump. (It also acted up when driving on the highway.)