Hey guys, first time posting on this site, i searched as much as i could with out finding anyone with a similar issue . I have a 1986 Mercedes 560SL. i bought it with a high idle not knowing what a problem this could be. The car is hard starting (a little better when warm but not much) but once started ran fine and drove well. I checked allot with the help of the forum and a good friend who understands electronics like the idle motor and a few other things but nothing helped (did a full tune up also) i kept reading about the OPV relay and the fuel accumulator being the cause of most peoples issue. So i purchased a OPV relay and the Accumulator but decided to only do one at a time so i knew what each was up to. i changed the OPV relay 1st. after changing it the car started immediately (before would be 20-30 seconds or more) and ran great, seems to run better than before cleaner and smoother. i drove it a bit and was happy with the results. im kind of a preventive maintenance kind of person so i decided to change the Accumulator a few days later (only really drove the car 20-30 miles before) i went to drive the car home from my shop and about 10 miles into the drive the car started running real rough and with in a mile it seems like it ran out of gas or maybe has to much fuel. i was not sure what happened so i called a tow truck and brought the car back, the next day the car started fine and ran for a short period but it seems to be dumping allot of fuel and stalled out again. I changed the accumulator back to the old one and it was the same ? i then changed the OPV relay back to the old one and although it was hard to start again the car ran fine and i was able to drive the car around again (still hard to start and has a high idle)

i thought maybe the OPV relay was just a bad one so i ordered a new one, i installed the new one and again it started immediately and seems to run fine but after a short time you could tell electronics took over as the idle raised and dropped a little and then it started to run rough again and seems to be dumping to much fuel (smoking out the tail pipe) and stalled the motor again. I then just changed the relay back to the old one and again its hard to start and has the high idle but runs fine. anyone have any experience with a situation like this or an idea what may be causing this ? ---- Thanks

 

Just a guess here and I'm not sure I'm qualified to give any help but for what it's worth: maybe with the old OVP you are not getting any power to the ECU and the car is running but in limp mode. Seems OK but not really doing what a KE Jetronic can do.

Now you put the good OVP in and car runs good until it reaches operating temp, KE stuff kicks in to adjust fuel, air etc. But the computer may be getting bad inputs causing it to run rough.

I think I would next check the oxygen sensor. There is a green wire going to the O2 sensor to the ECU. Behind th he passenger foot well you will find the ECU etc along with the plug for the o2. Do a voltage test. The voltage should be about 450 milivolts. As it gets to temp the voltage should vary 400+ / - 350 mv. This is telling the ECU how the engine is firing. If it reads incorrectly it is telling the ECU to falsely change the fuel mixture.

There is lots of info out here about o2 sensors and checking them.

At the same time you will probably need to check for vacuum leaks. They cause the same bad ECU input. A smoke test will reveal where the leaks are.

After determining a good o2 and tight vacuum your next target should be the fuel injectors. If they are old they probably do not shoot a fine spray.

Of course just about everyone will suggest a new distributor cap and rotor and some suggest new plug wires. As regular maintenance replacing these old parts is a good idea.

If th o2 is good, then you will need to dive into the cold start valve, coolant temperature sensor, idle control valve, AFM potentiometer, and EHA valve.

Hope this helps. Lots of info out here.

 

Hi All,

I have a 1986 560SL purchased new by me in 1986 that only has 31,000 miles on her.

It has been garaged since new and not used in winter, serviced as needed but........

Question regarding idle.

Cold or warm, A/C on or off my idle is 1,000 and in drive 750 maybe 800 .

I see according to many posts that idle and drive should both be in the 650-750 range and wonder if anyone has an idea as to why I'm @ 1,000 in neutral and 750 in drive.

Any ideas as to why I'm getting what I am and what to look into for a fix?

THANKS, Steve

 

I would suggest you check out your Over Voltage Protection relay. Could be a simple as a blown fuse on top of the relay. Nxt step could be many things.

At that point you would be better to Start your own thread.