OK,,, how do you find a vaccum leak ?
 

And positively eliminate that as a possibility of a surging idle ? My 95 E320 has been giving me fits for about a month now. I have decided the wiring harness is not the cause as I have cut it apart in numerous places and it is like new. Plugs and wires are 1 year old. Purge valve seems to be working, the O2 sensor and the water temp sensors are new. There are no leaks in the intake as it was just off for the EGR tube replacement and all fittings are tight. I have good ground at the O2 sensor and have cleaned the MAF. The obvious vaccum lines are good and connected but I would like to be sure that vaccum is not the problem. I read in one thread that a mechanic found a vaccum leak in about 15 minutes that wasn't obvious. How do they do that ? Oh yeah,,, still getting code 13 on pin 8.

Some shops use a Smoke Gun to find vacuum leaks.
The actually inject smoke into the intake manifold.
Seen it used a couple of times & found it pretty slick. ;)

Good stuff Mike,,, will try the ether thing tomorrow, but what if the leak in in the passenger compartment somewhere. There are tons of vaccum lines under the dash.

That is very interesting also. If I get some smoke inside the car I guess I'll know where to look.

Peter:

I may stand corrected, but the vacuum system(s) you would be spraying under the hood are isolated from the vacuum lines inside the vehicle in so much that you would not draw starting fluid inside the vehicle.

Perhaps a pro tech will chime in and confirm this.