R129 Erratic Idle

[sideshowbob]

Hi All,
My 1995 SL500 has an erratic idle. It generally only happens once the engine has warmed up and is as if it is hunting. It is rather off putting because when i come to a standstill it feels as through the engine will stall.
I have had the throttle actuator refurbished, and the wiring loom replaced last week in an attempt to solve the problem, but this doesnt seem to have made any difference.
All help very gratefully received.

 

[sideshowbob]

Here is a quick video of the car at idle this afternoon. Marvel at my ****** rev counter!
SL500 Erratic Idle.MOV - YouTube

 

[ed_d82]

Have you figured out what the issue is? Is it like that all the time?

 

[sideshowbob]

I have absolutely no idea what the issue is. Thats what im hoping someone on here may be able to help me with. The problem seems to happen once the engine has got up to temperature and is then at idle, such as stopping at traffic lights or waiting to pull out of a junction.

 

[SavMan]

Possibly the Crank Position Sensor starting to go.

 

[SavMan]

http://www.mbclub.co.uk/forums/engine/79244-sl500-r129-misfire-idle-what-next.html

Interesting thread for you with a list of some things that you may want to consider.

 

[sideshowbob]

Thats a scary thread! I dont have all those problems. The car runs fine apart from an idle that hunts. Apart from the Crank position sensor is there anything else simple i can get checked?
Thanks for going to all the effort of hunting out that thread and posting it up.

 

[rorf]

As it only happens when the coolant has warmed up I would suggest you check the coolant sensor which sends a signal to the ECU - when cold the ECU allows a slightly richer fuel mixture. The other coolant sensor is for the temp gauge.

 

[jeff500sl]

Check all the vacuum pipes are connected or not leaking.

 

[sideshowbob]

Thanks guys for all the suggestions. Car went back into the garage again today (this car is proving to be a very expensive purchase), as soon as i hear anything i will keep you all updated.

 

[Torqueofthetoon]

Hmmm

I had a similar erratic idle problem on my C320 CID and it was tha mass air flow meter. It was changed under warranty and job sorted. It was an easy problem to detect for the dealer and the orange engine warning light came on to let me know something was up.

 

[rod63]

I had a similar problem on my 1991 r129 500Sl, the idle was erratic, replaced all the plastic tubes on the intake to the filters (they were craked) and the problem was solved.

 

[OKZ4800]

rotor arm adaptors?... My 1990 SL500 was the same. Car had sat for ages before my buying. The garage said it was running rough and needed to get it running before I picked it up. I got the call to say all was good and I picked up my new pride and joy only to find after a week or two the car started popping and spluttering when warm until eventually it was awful and unusable. I was advised by a local mechanic friend to change leads, this I did to no avail.Upon investigating on the internet I found threads about rotor arm adaptors that MB recalled for replacements as these crack the base of the rotor arm after a period of time and upon checking mine I noted that a new arm had obviously been fitted by the garage immediately prior to my collecting the car, obviously this solved the problem for a VERY short time. The new rotor arm already had noticeable pitting and deterioration, the other was very poor and so I ordered new rotor arms and adaptors, changed these and bingo, problem solved. There are part numbers for the superseding adaptor replacements and good advice on the web but at present I cant recall where I found this. I did get the parts from AI in america but I guess these are readily available in UK with a bit of hunting. I am no mechanic, certainly a novice SL500 owner but was pleased to solve my issue on my own and so offer this advice in the hope it helps someone else?

 

[ShinyF1]

I see you also have the 'revcounter sitting 20° off centre' issue I've seen on half the cars I've viewed so far.

Good luck solving the problem