93' 300E idle problem/question
 

Hello guys! I have been noticing something that occurs sporadically when I come to idle:

The RPM indicator will go up to 1,000 and then back down to 500, then it goes up again then down......
As I mentioned, it happens when I am in Drive and am idleing. Can this be a serious matter? Is there something I can check or is this something that happens to others?

My car had a fluctuating idle that was exactly what you are describing.

My problem was a vacum leak - at the intake manifold - which is quite an unusual place for a vacum leak.

A vacum leak (anywhere in the system) is "false air", and prevents your mass air meter from figuring out the proper air / fuel mixture. The idle will hunt up and down, trying to find the right mixture, and can't because of the vacum leak, and keeps hunting.

If you don't have a vacum leak, then your mass air meter may simply be defective.

Additionaly, a defective throttle actuator will exhibit similar symptoms. The throttle actuators have pentiometers that go bad over time. They also have a wiring harness that goes bad - just like the engine wiring harnesses that fail in all M104 engines from 1993-1995.

The first thing I'd check is for a vacum leak, i.e. a vacum hose that is cracked or that has become disconnected.

There is also a lot of information in the archives to add to my post.

Here is a result of the words "vacum leak" under the user name "Arthur Dalton".

He has a car like ours and has posted frequently on vacum leaks and the sources of problems.

http://www.peachparts.com/shopforum/search.php?action=showresults&searchid=943321&sortby=lastpost&sortorder=descending