of course you have the updated wiring harness and checked the wiring on your Electronic throttle, right? These issues cause codes to trigger due to electrical faults and rough idle is always part of it, surging and missing. My 94 sedan had an upgraded harness but still had bad ETA wiring as indicated by the cruise control dropping out whenever I hit a bump, but otherwise it drove great..

Lots of comments about those issues here in the W124 threads. No need to repeat.

Enough folks have mentioned it that I need to confirm for my own sanity. Could anyone point me towards some instructions on checking the date of the harness? I searched through the forum but nothing jumped out at me.

My pops told me his mechanic put in a new harness, but I actually do not have confirmation that it was a new harness (i.e. mfg after 98) as opposed to a crap harness that is new to my car. As he tells me, the mechanic went to the junkyard himself to make sure it got cut out at the right spots, which makes me question what he did.

Also puzzler, could you clarify what you mean by checking the wiring at the ETA, I am not familiar with all the components of the M104 engine yet?

Thanks all for the input, this has been wicked helpful

Ok well my suspicion is now confirmed... The dude either put in another old harness or spliced a new one in, leaving all the electrical plugs. He always struck me as really lazy so either is possible. I found a few stickers with the FD as 94, plus the part on one of the stickers is (it looks like) the old model (124 440 56 32). I did find a cracked and corroded lead back in the battery, but a spot check of the others did not show visible degradation. Looks like I need to do a new harness. Any suggestions on best way to go about this?

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gjones8131, you should acquire either a new wiring harness, or a replacement wiring harness in good condition that is meant for the VIN of your vehicle. A new harness will come with all the connectors needed to install it in your vehicle. If you lay it out near/atop your engine it will be simple to see the connectors that you need to disconnect in order to install the replacement wiring harness. It's not very difficult, but takes some time and patience.

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Fred Hoelzle