I HAVE A 89 300SEL WITH 150K KM. THE IDLE ON THE CAR IS ROUGH. THE RPM NEEDLE FLICKERS SLIGHTLY AT IDLE. ALSO ON CLOSE OBSERVATION THE OIL PRESSURE NEEDLE IS ALSO FLICKERING. THE ROUGH IDLE SENDS A SMALL VIBRATION IN THE BODY OF THE WHOLE CAR. A HAVE THE MANUALS OF THE CAR BUT THE TESTING DESCRIBED IN IT INVOLVES A LOT OF SPECIAL INSTRUMENTS AND TESTERS.
MY QUESTION IS ARE THERE SOME BASIC THINGS TO CHECK WITH A MULTIMETER REGARDING THE ELECTRONIC COMPONENTS FOR THE IDLE SPEED.ALSO IF THIS IS NOT FIXED IS THERE ANY LONG TERM PROBLEMS WHICH WILL DEVELOP.
THANKS IN ADVANCE

In most cases the electronics on cars don't cause running problems. Have the basic items tested, like the compression & the ignition system. If you still can't find the problem then have someone check the fuel injectors.

Also, engine mounts were always faulty on these models...This will cause a severe vibration at idle.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Thanks for the reply

The car had starting problems last winter (-15 deg C and below). For this problem the dealer replaced the fuel injectors, ignition coil and also a reference resistor( as part of MB bulletin). Also the engine mounts were replaced 2 years ago. Any other tips. What is the function of the two small shocks (dampers) beside the engine mounts. Do they help in removing small engine vibration. Also how do you check the idle air valve, would it play a role in the rough idle.
thanks in advance.

[This message has been edited by SANDEEP (edited 06-15-99).]

My '92 400SE used to vibrate, and has rough idle, even hesitation, too. And after checking through the basic stuff, they found out that the distributor caps are wear out. And later find out that the connector(don't know what they call it)between coils and spark plugs are bad. So, they changed it. And now runs very smooth(except that I still need to replace the worn engine mounts).

Hope this helps....

Andy Kuo
'92 400SE
69000KM

Need some tips or things to check from the MB experts.

Suggested you start W/basics ie compression test. Have the ignition system tested on a "scope"? What condition is the "secondary" ignition system in? To diagnose such a problem these items are very important!!
With this type of fuel system the electronics only enhance the basic CIS fuel system. Most cars will run even if the electronics fail. This is why M.B. stayed with CIS when all other car makers went back to complete electronic systems.

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS M.B. TECH