1990 500 sl, 5.0 v8 - merc 500 sl cuts out on idle/tickover

Honest John Back Room » Technical matters
View Threaded
Wed 23 Jul 2014 21:49
1990 500 sl, 5.0 v8 - merc 500 sl cuts out on idle/tickover - carnut1980

my merc sl 500 cuts out on idle, drives ok, pulls well, but rev counter doesn't work so no way of telling what its doing on tickover. in traffic i have to keep shifting to neutral to keep it running. leads and plugs are good, caps and rotor arms are new. 143k on the clock. Do these have idle control valves? is there any way i can get under the bonnet and increase the tickover rate? i have to give it some revs in neutral while raising/dropping the roof. please help!

Reply | Report as offensive | Link
Thu 24 Jul 2014 10:31
1990 500 sl, 5.0 v8 - merc 500 sl cuts out on idle/tickover - elekie&a/c doctor
Iirc,this car has electronic throttle control,so no idle valve,and no mechanical adjustment.Make sure the throttle body and butterfly flap are clean.If you can find somebody with the old style MB diagnostic system ,there is some self diagnostic info available.
Reply | Report as offensive | Link
Mon 4 Aug 2014 19:51
1990 500 sl, 5.0 v8 - merc 500 sl cuts out on idle/tickover - carnut1980

this car does indeed have the ICV, part number 0001412425. I removed and inspected it and the plunger moves fine, i understand there is an overload protection relay that can fail and cause these symptoms. Does anyone know where the relays are? they aren't in the fusebox under the bonnet. What else can cause the erratic idle? thanks

Reply | Report as offensive | Link
Mon 4 Aug 2014 19:56
1990 500 sl, 5.0 v8 - merc 500 sl cuts out on idle/tickover - elekie&a/c doctor

Can you confirm whether this is a w 107 model or a w 129 model.Looks like your original post said disributor caps,so i guess this a W129 model.

Edited by elekie&a/c doctor on 04/08/2014 at 19:57

Reply | Report as offensive | Link
Tue 12 Aug 2014 21:41
1990 500 sl, 5.0 v8 - merc 500 sl cuts out on idle/tickover - carnut1980

hi this is the r129. Seemed to be running rich but a small adjestment on the screw and its running better, though still needs gas pedal on startup. rev counter doesnt work at all. Any idea what this could be?

Reply | Report as offensive | Link
Wed 13 Aug 2014 08:21
1990 500 sl, 5.0 v8 - merc 500 sl cuts out on idle/tickover - craig-pd130

My brother-in-law had an R129 500SL with intermittent cutting-out problems. Turned out to be a faulty crank position sensor. Once replaced, it never cut out again. The Merc indie specialist who diagnosed it said it was quite a common problem.

This could also explain the dead tacho, although I've no idea if the tacho takes a signal from the CPS.

Reply | Report as offensive | Link
Thu 14 Aug 2014 13:47
1990 500 sl, 5.0 v8 - merc 500 sl cuts out on idle/tickover - barney100

Suggest you join official MB club and their dedicated section for your model will be of great help. Plan B would be to use a specialist MB indie.

Reply | Report as offensive | Link