1988 mercedes 300 rough idle
 

Hey,
I have a 1988 mercedes 300 and at low RPMs it seems to run really rough. Once I get going it runs fine. At Idle it runs around 750rpms but shakes alot. If I then hit the gas it will RPMs will drop to almost nothing and in some cases stall out. It will also do this when i switch from nuetral into drive or reverse. But like I said once I get going it runs fine. I have had 2 machanics look at it, one said it was the Valve guides adn the other said it was the fuel injector. I was just wondering if any other people had had this problem and any advice would be much apprecciated

thanks

It may be the OVP...
 

Have you done any electrical work later...? are any lights on in the instrument cluster...?

Start there...

No new electrical work or lights on the cluster. Recently had the valve seats replaced becuase it was blowing oil.

Then I would check all the rubber hoses...
 

specially the ones under the fuel distributor and the injector seals. The easiest way to check the injector seals is by spraying carburator cleaner around the seals and see if there is any change in RPMs (do this at your own risk). It work for me...

I would steer clear of the guy with the valve guide story. Injectors possible I suppose, but as mentioned already, I'd be suspicious of loose/leaking vacuum hoses, idle control valve, throttle position sensor.

Over the years, there have been countless writeups here about these sort of problems with 300Es and any car for that matter with the M103 motor.

I would query the SEARCH function. Long list of possiblilties.

Sounds like your EA, exact symptoms I had. BUt not sure if this model had one or not.

Take a look at my username and our 1988 300TE.
Look at your plug leads, even if they look ok and are recent.

I had the same symptoms on mine - at idle/low rpms, it shook. Smooth while driving. Turned out to be the engine mounts. For an '88, if you haven't had the mounts replaced, they're due. ;)

If you have the common front timing chain cover oil leak, oil can get into the distributor cap and cause a rough idle as well, from fouling the contacts.

I had a similar set of problems. I sprayed each of my injector seals with carb cleaner. Spraying #3 resulted in a serious drop in revs. The seals are $1.70 apiece and made a big difference for my car. I just swapped them out tonight.

To do this, you will have to remove the injectors from the car. That involves undoing the fuel line (hold the line while twisting the nut) and taking off the bracket. From there, I had to cut the old seals off with a wire cutter. There is a little ridge that holds the seal in place.

While I was at it, I replaced the water temp sensor, which I knew I needed to do because the car ran ok cold, but stumbled at speed. That took a 22mm DEEP socket.