New member: intro and some questions

[MBZ Drvr]

Hello all. I recently picked up a 1989 300E with 88,000 miles. It's clean inside and out. I've been working my way across the instrument cluster making the warning lights go out and making the gages read happy values. so far, I've replaced the fuse in the ovp relay, replaced the fusible link for the fan, replaced the wiper pumps. cleaned all the fuses, cleaned all the light bulbs., and topped the fluids. Oh yeah. 4 michelins.

Now that the warning lights are all dark, I can move on to the next set of issues . This is where the questions arise. First, the are fast idle problems. When the engine is cold, I start the car and it wants to idle around 1000( as read on the dash, in park (occasionally.it idles as high as 1300 or so. in either condition the only fix is to turn the car off and restart it. This almost always fixes the problem. Turning the AC on full blast has very slight reduction in idle speed maybe 100 rpm drop for a second or less.

Ideas?

Any suggestions for service manuals for this car?

[ps2cho]

I would go ahead and replace the OVP completely first. It fails internally and if its original, it is time. (AVOID ALL URO PARTS -- Documented garbage)

Since you are new to the car, do not jump start the car with a boost charger or jumper cables with another vehicle, ever. This destroys the OVP and MB has made note of this in bulletins. I recommend owning a portable battery, just plug it in, turn it on and start car since it only acts as another battery, and not a boost charger.

[JamesDean]

For a service manual, Mercedes recently posted them all online free for use, here is a link to the 124 manual:

https://www.startekinfo.com/StarTek/outside/12264/?requestedDocId=12264

https://www.startekinfo.com/StarTek/outside/12264/Program/matrix.htm

As for the high idle issue:
My 190E would do this from time to time. I actually think its somewhat normal for the car to high idle (~1000rpms) on a cold-start. Once I get the car in gear and driving the idle returns to a normal 700-800 rpms.

[davidlee]

You might possibly be looking at getting an other fuel distributor.
Its the thing that sits under your air cleaner that has all the hard fuel lines connected to it, if that ends up being the culprit, they are still easy to find.
they are prevalent in the pick n pull yards around. you can get one from a
190E 2.6
260E
300E
if you grab one from a yard, get the whole thing as a unit, air flapper and all
dont disassemble it down to its bare form, its easier to change out then, and less parts to take apart, I have had to do it to 2 diff. Mercedes over the years. cured the idle issues, and i also had problems at full throttle, it solved that too.

[ps2cho]

In my experience junkyard distributors are a real gamble. 90% of the time they are bad due to sitting gas and mileage on the vehicle.

Start with the OVP and report back...You have to get a baseline done first. Once that is replaced, then start with a basic tune up. Plugs/Wires/Rotor/Cap.

[Jim B.]

I'd zero in on the idle control valve.