300E 1988 Rough Idle & Best Service Manual?
 

I have a 1988 300E that accelerates and performs well but idles poorly and will occasionally even stall. The car has 104,000 miles. I bought used and not sure of service done on car. Any suggestions?

Also, cruise control will accelerate car but not hold a constant speed. Any suggestions?

Also, I have service manuals from Benz but they offer little detail. Any suggestions for manuals under $100?

Thanks,
billw7

First thing to check is spark plugs, to see if they are worn, also the spark plug wires and distributor cap and rotor. If you haven't done a tune up on a Mercedes Benz the wires cap and rotor are rather expensive as compared to most other cars.
If this does remedy your problem, then check back with the forum for more advice.
Good luck.

My advice:

Take two bottles of Techron and call me in the morning!

Seriously ... try it.

You have only less than $20 to loose.

Stalls are usually a sticking idle control valve -- its under the air filter, silver can with a two wire connector and two large rubber hoses attached. It controls the air flow through the fuel distributor at idle, and it closes completely at speed -- if it doesn't open as you slow down, the engine stalls. Starts right back up. If you usually have the problem after abrupt stops, it's the idle valve.

Rough idle has more causes. Leaking vacuum lines is one cause -- I initally fixed most of the problem with my TE by replacing all of them, including the idle control valve hoses (big pain, but worth it, they were actually rattling on the barbs). The overvoltage control relay (OVP relay) can go bad and intermittantly disrupt the mixture control circuit. These eventually need to be replaced anyway, I think, as they will fail sooner or later. The electro-hydraulic actuator that control the pressure differential in the fuel distributor can go bad -- it leaks when it does, so if you smell fuel once in a while, suspect it! -- and will cause both idle roughness and bad fuel milage.

And last, but not least, bad engine mounts will cause a rough idle sensation -- if it is not too bad in park, worst in drive, and goes away or gets much better in reverse, you engine mounts need to be replaced. 100,000 miles is kinda soon for engine mounts, but not impossible.

Lots of posts on this issue, use the search function and ask more questions!

The CC issue is a bad amplifier -- you can either replace it or take it out and re-solder the connections (may and may not work). Also, check that the brakelight bulbs are good and matched (some people recommend only Osram bulbs) as the CC grounds via the stop lamp filament.

Peter