95 s320 strange hump (?) at cruising speeds

[PutPutPut]

Hi,

I had attempted to search, but not idea how to verbailze the proper terms.

1995 s320 w140 with 325k miles.

Last night, while cruising home between 65 and 80 mph on the freeway, the car sort of "humped" every now and then.. like it was losing power for a second, then regaining it - each hump took about 1/4 of a second. The rpm gauge fluctuated with this hump feeling. Sometimes it would hump multiple times in a row. It was kind of like a mini-shift?

Appreciate the help in terminology so I can search, or if you have a moment to help diagnose, would appreciate it! Transmission? Spark plugs? Electrical? Battery is fine. The alternator was replaced about 3k miles ago, but the inside of the engine is covered in soot and old oil and crud for 300k+ miles. Intend on having that cleaned at some point - maybe that's coroding the electrical?

[Matt L]

Do you know if your wiring harness uses biodegradable insulation? I don't know, but if so, it could be the problem.

You also probably have a CPS in that, like in the early 210's, and that can cause problems but usually it causes the engine to quit completely until it cools down a bit.

It seems logical that if it were an wiring or sensor problem that your tach could be affected.

[PutPutPut]

Yep, 'twas the wiring harness, boy it's expensive