Cruise control and idling issue - W124

[Pottering]

About 3 months ago my cruise control started operating intermittently, then finally stopped working. Just after this I noticed the car was idling at around 1100 rpm. Can't say if this occurred exactly when the cc died. Mechanic checked it and pronounced the throttle body was faulty. Had a reconditioned throttle body installed but only change was now idling at around 1300 rpm and occasionally fluctuating 1000-1300 in P and N, but steady in D. No cc. Cruise control amp (124 545 52 32) was then isolated as the cause.

In Australia it is very difficult to get these and quote was $2000 ex Germany. I've read quite a few threads here about having the CC module resoldered. I wouldn't attempt that myself (Mr Butter Fingers), but I'm assuming a decent auto electrician could do such a job. Though I have no proof of a upgraded wiring harness everything looks in good condition and the old throttle body harness was near enough to pristine.

Has anyone else experienced such issues and can advise on what might be the best course of action.

1994 E320 coupe, M104 engine, 722.5 transmission

Pottering

 

[Ade B]

Have almost identical intermittent symptoms...

Might be worth a look at this if you haven't already.

Ade

 

[Pottering]

Problem finally fixed by a remanufactured throttle body. Not as easy as it sounds, first three supplied throttle bodies were inoperative. Supplier kept sending units (he was a distributor, not the manufacturer) and eventually hit pay dirt.

Idle is now steady around 750 revs and cruise control working again. Took almost a year to sort out!

 

[mattc]

result!

 

[Pottering]

About the same time this idle problem appeared downshifting became temperamental. Very reluctant to downshift unless really booted. Mechanic thought linked to idle issue and wanted that sorted first. Once idle was good he determined that a gearbox solenoid was faulty. Cleaned up the wiring, ran Star diagnostic and cleared error code that was probably caused by the initial throttle body going on the blink. Gearbox now smooth and downshifting beautifully.

These two issues had the potential to be majorly expensive ($2,000 for a new throttle body and write your own ticket if the gearbox had to be opened up). By a bit of perseverance all got sorted at pretty reasonable expense (about $1,000 all up including labour).

Anyway I'm happy I hung in there because with these cars there can be moments were the looming costs can seem to be not worth it given the car's nominal value. Of course if you value it at more than the book price you'll try and find a way to get it done.