Hi all, I have some running problems on my G320 and need your suggestions. This is a 1995 model with the M104 engine.

Problem 1: When cold, if I start accelerating the truck pulls power back. This happens gradually over a couple of seconds, to the point where the engine is just sputtering (and I sometimes hear a clanking in the engine bay, like the timing is being pulled back violently against a rev limiter - but engine is only at around 1000-1500rpm at that time). If I let go of the accelerator, on the 2nd or 3rd try the truck seems to wake up and start acting normally, but it will happen all over again after the next traffic stop. This happens until 5-10 minutes of driving and the engine is warm.

Problem 2: Once the engine is warm and first enters closed loop mode, the idle at stop surges. The truck feels like it is about to stall and then picks up the idle and then drops again. This happens erratically, and less so once the engine is even warmer and has been driving for longer (~30 minute drive).

I recently had the head gasket replaced, since it was leaking and there was white smoke at startup. Also the upper timing case cover had corrosion (this truck sat for a few years before I bought it, but had low miles) and an o-ring on it almost got sucked into the engine so I'm glad we did the work now. The above two problems existed before, but are more pronounced now. When these problems are not happening the truck runs better than ever before with good power.

Things recently replaced as part of the head gasket work, just because we were in there:
- spark plugs
- ignition coils
- mass air flow sensor

2-3 years ago we also replaced:
- engine wiring harness (I had no running issues at the time, but the original wiring insulation was coming apart)
- throttle body (replaced with a rebuilt unit since we replaced the engine wiring harness)

Any ideas? Thanks in advance.

__________________
1985 190E 2.3-16 Euro

I'd be looking at the crankshaft sensor.

Have you scanned for codes?

I'd unplug the EGR vac hose ( if equipped ) as a test.

I'd also unplug the intake cam advance electro magnet to see what happens.

Turns out my problem was with the oxygen sensor, which was just 1 year and <10k miles old. However, I had an exhaust manifold leak which wreaked havoc on the sensor. Welded up the manifold to fix the leak, replaced the oxygen sensor, and all is good now. No codes came up, but the voltage for the oxygen sensor was all over the place even at idle which helped pinpoint the problem.

It was an interesting problem and solution, I hope this helps someone else. What baffled me the most was that I did not know the oxygen sensor played such a big role on cold start in open loop mode so I did not even consider that initially as an item to look at.

__________________
1985 190E 2.3-16 Euro