M119.980 engine rev surge and cut out

[IMD]

Hi everyone, I hope all's well.
I have a 1997 SL500 R129 (not a 500E!), but it has the same M119 engine. This forum seems quiet active, so I thought I would ask here.

I've been having an intermittent problem with the car for a few months now.

On most journeys, the engine will occasionally die when I pull up to stationary, in traffic or at stop sign etc. This doesn't happen every time I stop, just maybe once or twice on a longer journey, sometimes not at all. It seems to be when the revs drop. It drives perfectly well and I have no issues at any speed.

I have noticed that there will occasionally be a sudden slight surge in revs, as if it is trying to correct itself. If I'm in gear, this will move the car forward! It then settles and often, this is a sign that it will soon die. When it does die, it's instant. Lights come on the dash and it's off, as if the ignition is switched. It always starts perfectly straight away afterwards and then may drive for many miles without an issue.

I had an independant specialist here in the UK check it over. They thought at first it might be the crank shaft sensor, so this was replaced, but it made no difference. They said they checked the loom and it looked fine. My understanding is that loom issues affected up to 1996 models. Is that correct? They check the fuel pump and no issues and there were zero fault codes showing for the car.

I have read a few other forum posts with similar symptoms and some say it could be the MAF, others the vacuum lines, others the ECU and others the engine loom, but as often is the case, they never post what corrected it.

I have contacted another specialist who knows these cars, but I wanted to see if anyone has had similar issues and found a solution.

Thanks, Ian

 

[TerryA]

Hi Ian,
It sounds like a vacuum leak to me. Unless they have been changed on a 97 engine your vacuum hoses and connectors should be pretty brittle by now and can crack. Since the engine runs good most of the time there could be a cracked hose or little plastic connector that opens and closes in different torque situations.

You need to go thru all of the vacuum hoses and connections. I’m sure someone has the schematic of the lines here.

Good Luck

 

[gsxr]

There are no wire harness issues on your 1997 model (those only affected HFM and LH-SFI engines through 1995-ish).

I also suspected the crank sensor, which is a fairly common issue on the ME-SFI engines, but you said a new one did not make a difference.

Wouldn't hurt to check the battery terminals and verify they are tight, also any other electrical items, especially anything that was touched in the past few thousand miles or so. Stranger there are no fault codes.

 

[emerydc8]

Does the 129 have the same ETA that goes bad, Dave?

 

[gsxr]

Does the 129 have the same ETA that goes bad, Dave?

Yes, but only for LH-SFI engines (119.97x).

The ME 1.0 systems (119.98x) have completely different ETA's and MAF's.