Idle problems in a 1970 300SEL 3.5

[SickFinga]

I recently got a 1970 w109 with a 3.5 engine that got idle problems and to be honest, don't know where to start.

Before picking up the car the seller and I drove to a mechanic to do safety inspection and it already had idling problems but not as bad as I'm having right now.

Before picking up the car it would actually drive and idle semi-ok , it would stall if the brake is applied. That leads me to believe that there is a vacuum leak.

Right now it doesn't idle at all, also it sounds like not all cylinders are firing up and the car barely responds to throttle.

Anyone got any suggestion what should I check?

P.S. Does air suspension somehow required for the engine to run properly? I'm asking because right now I got all the bellows removed.

[mak]

Hi
the air suspension is independent of the engine vacuum . if you have removed the air bellows then the air compressor belt should be off as well.
I asume you have replaced the bellows with coil springs and the front is very low

Mak

300SEL 3,5 Euro 1971

[mak]

Among other causes the trigger points for the fuel injection ,the lower part of the distributor may be dirty causing erratic idling .
mak

[Tomguy]

I 2nd the trigger points notion. I have suffered from dirty ones, and it can cause a rough running, low-powered engine. However, I don't think it's your only cause as the engine should still be able to idle and run on only 4 of the 8 cylinders. If you combine a severe vac leak in the booster with firing on 4 cylinders only, I could see a stall condition. I would also check common items like fouled ignition points (clean with an index card), bad distributor cap, loose wires, and fouled plugs.

[SickFinga]

Thank you guys for all your suggestions. I replaced distributor cap, ignition wires, spark plugs and vacuum lines. That did not solve the problem, but I'm pretty sure I found the problem.

This plate was/is the problem



Between those 2 plates there are plastic "feet", something like under a computer mouse that make it slide more easily. So one of those feet got lost and the plate wouldn't turn as easily and sometimes would get stuck completely. I made a homemade "foot", it got better, but the plate still doesn't turn as easily as it should.

So my question is, is there a rebuild kit for that kind of distributor, or a place I can buy that plate thingy?

[ctaylor738]

Mercedes does show a "Repair Kit," PN 000 586 28 15, but I have no clue what's in it. They also show the distributor as available.

[Tomguy]

That shouldn't be causing your idle problems, but it may point to your timing being too far off. Timing should be 5°ATDC WITH the vacuum retard. It may have not been retarding, so it could have been 5°ATDC WITHOUT the effect of it (when it should be ~12° more advanced, ~7°BTDC, without vacuum retard). That can cause no power, poor economy, and idle issues as the engine isn't meant to idle 17°ATDC.

These are 4.5 numbers, the 3.5 numbers may be different for suggested timing values (my book isn't here), but the 12° difference will be the same. And as the 3.5 is a higher-compression engine, it will make an even bigger difference than on a 4.5. The vac retard is primarily for emissions and you can plug the line and set timing 12° more advanced than the plate on your crossmember suggests - even if you don't really want to as a permanent solution, just do it temporarily to rule this out as the cause. You can pick up a used 3.5/4.5 distributor and just swap the top plate if your mechanical advance isn't frozen, too. Now to check my basement to see if I brought that box of spare parts when I moved!

[SickFinga]

Originally Posted by Tomguy

Now to check my basement to see if I brought that box of spare parts when I moved!

Any luck finding that box? Looks like I'll need a distributor or just the plate.

[Tomguy]

I have a distributor plate. I'll see if it's any good. PM me if you want it.