Hello:

I'm new here, and to W124. Got an used W124 E220 several months ago. I've got a problem here related to stuttering/misfire.

The engine would start from cold and run fine. It did run without issues for several weeks. The only thing I did before the first time this problem occurred, was my filling up the tank and pressure washing the car. It was the night before I took the trip.

The first time it happened, was on the highway, over a fairly long uphill in a tunnel. I noticed the engine was vibrating, as if borderline stalling. There's a loss of power where I couldn't add more speed over the long uphill. I tried to add more gas, but it only seem to make the vibration worse, and then the exhaust started some backfiring. I tried to cruise as much as I could by feathering the pedal off to the service roads, without shops or support. The car would initially run/idle somewhat roughly, but it never stalled. I stopped running it to let it cool (it was during summer and the AC was on), and then tried to start it, drive it with the AC off, and found the problem intermittent. I was trying to figure out how to get home, but the symptoms seemed to have subsided. I tried a few more runs, and while the engine sound felt a bit coarser (like it has a sore throat rather than the usual smooth hum), it ran mostly okay. I eventually drove on the highway and lots of local roads, for over 100km back home, with the AC off, without having the problem occurring again. It ran just fine all the way home.

The 2nd time was when I had to drive to the local inspection station only 5km away. It ran mostly okay, but then again on the way back, I had AC on, and over an uphill, the stuttering occurred. I had to pull over, turned off the AC, revved the engine, which then sputtered a bit at low rpms, before revving normally to higher rpm. Revving it several times seemed to have cleared something? Then I got into gear and drove it home which wasn't far away.

A bit of history: when I got the car, there sounds like a sort of pinging noise coming from one of the cylinders when the engine got hot/normal operating temp, and when i started accelerating. I think it's still there. I tried to add techron to fuel in attempt to clear injectors, but after several bottles of that it didn't make a difference. I tried higher octane fuel and it didn't help. The fan clutch failed and caused an overheat one time and got replaced. AC refrigerant was vacuumed out and replaced when I first got it.

So right now I *think* turning on the AC, adding to the load, kinda causes it to happen. Going uphill seemed to be a factor too. I'm thinking it's some sort of fuel starvation issue? If plugs/wires have gone bad, it shouldn't have recovered at all the way it did?

Any inputs/suggestions/guesses would be very much appreciated. Thanks so much.

 

W124 had a problem with the engine wiring harness rotting. Might this be causing your problem?

 

I *believe* the wire harness had been replaced, as it didn't feel crummy and felt like it's not as old as the car. It's not shiny or anything, but it looked and felt fairly solid to the touch? Also wouldn't rotting harness result in constant running issues, rather than intermittent ones? I don't know really.

I drove the car a bit today for another scheduled inspection. Same long uphill right turn, but this time without AC, stuttering occurred. As soon as the car was more level, it managed to run okay again.

However, as I drove home, I decided to turn on the AC while the car was idling. Pretty soon, occurred, as if the engine was out of balance. I could rev up to make it seem less obvious (whatever caused it was probably still there as it didn't feel as smooth), but as soon as the revs come down the vibration/shaking came back. Same symptoms as when it first appeared, and just like the first timeit didn't go away even with the AC off. It just kept on idling out of balance (misfire?), even with revving up the engine, AC off. I tried for about 15minutes before giving up. Coolant temperature was only slightly above 80C.

Going uphill as a trigger would be consistent with fuel starvation? Yet I don't get how the AC was able to trigger it on flat ground and even with it off, and revving, it wouldn't go away.