Hello all,

Just bought my first Merz. 89' 300E, 62,000K. Awesome little machine, just one slight problem.
When I first start the car, hot or cold, it will run rough for about 15-30 seconds. Then once I
flutter the gas pedal, it idles fine. Then the first take off feels like I'm on 5 cylinders if I depress
the gas pedal slightly. I just give it half a pedal and away I go. No problems after that. Runs fine,
until the next start. Hot or cold, doesn't matter. No ABS light is on. Don't smell fuel, or rich condition.
No smoke. Replaced the distributor cap and rotor. Added fuel/injector cleaner.

What I have gathered in the forum is this:
- leaky injector.
- couple different relays.
- fuel return valve.
- plug wires.

There have been people with this problem but not many post back what they found.

My thinking is either too much fuel on start - Leaky fuel injector.
or no fuel at start - leaky fuel return valve or leaky fuel line.

Any help would be apprectiated.

 

Ok, I wanted to make an addendum to my original note.

When the car is started, hot or cold, it will idle rough/eratic. If I
rev the engine, it will rev rough, vibration. Once I put the car in
R or D and go it will go sluggish the first time. Then once I drive about
5 seconds, it runs fine, purrs like a kitten for the rest of the drive.
If I stop the engine and restart, same process as stated.
I notice that once it is running good my idle is around 600-700 RPM.
In nuetral or Park it idles around 900 RPM. With car in park/nuetral
and A/C on it idles around 600 RPM and with A/C on and car in
Drive it idles around 500 RPM, yet purrs.

Only when it is first started and until I take off the first time in Drive do I have
the problem. If I let it idle for a while rev'ing the engine for a while, it will
not correct itself until I put it in drive and take off.

This, I think, negates the leaky injector or return valve problem.

 

you may need to check that one before proceeding.

 

Thanks sleepwalker, the fuel delivery system tested fine.
What I noticed was what I am assuming is the Mass Airflow
Valve, it's what I would view as the butterfly on the throttle
body intake, was hanging up. So I cleaned the air inlet
and it fixed that, but the problem is still there. Once the car
is started I can initially push down on this valve and get the car
to stop sputtering upon start. Once I do that the car idles at
900 RPM in Park and 600 in Drive/Rev. If I lift up on this valve
the car park idle sounds great. This valve seems very sensitive.
is there a way like on the older BMW's to readjust this tension
on this valve or is it electronic or vacuum adjusted.
The car has a eratic idle. Like I stated above all the different Idles
depending on situation. Even in Park and nothing on. The idle
varies from 500 to 900 RPM, like the A/C compressor is kicking in and
out, but it isn't.

 

Does the butterfly on the throttle body have a tiny hole in it that's clogged up? Since the butterfly was so dirty that it wouldn't close, it may be that the hole is clogged. Either a partially opened butterfly or the clogged hole will cause erratic idling.

 

Lugnut, thanks for the speedy response, I will check.
Is this butterfly suppose to be completly shut when idling.
When the car is at idle, warm, the butterfly is slightly open,
maybe 1-2 mm. How is this valve being controlled? Electric,
vacuum, mechanical?

 

I don't know the history of M-B throttle bodies so I can't say. My guess is electric and computer-controlled, which means you'd need a scanner to adjust idle, but sleepwalker can tell you that. In other words, if the mechanicals are okay, the computer can adjust the idle and you shouldn't have to adjust it.

If the butterfly is completely closed and the hole is clogged, then the engine dies because it gets no air. The hole supplies a minimum amount of air for idling. It doesn't take much gunk on a throttle body to affect idling, so when you said the butterfly was hanging up and needing cleaning, I mentioned the hole. You might want to remove the throttle body and give it a good cleaning front and back. It might be a good idea regardless of the final outcome.