Hi all. I am a newbie and this is my first post. I have lurked and gotten a lot of helpful info from the forum about brakes, oil, general maintenance, etc. but I am now stumped.

I have had my 88 560 sel for three years and has been great until recently. High milage but uses no oil between changes and everything works. The problem(s) are: It starts cold after a couple of revs and runs ok until it reaches temp 80 C. It then starts to idle very roughly and shakes the car. When I drive I can feel the hesitation and sometimes it feels like a headwind. When I idle in neutral with it warmed up it idles at 1000-1100 rpm. The real head scratcher is sometimes it starts and runs and idles with no roughness at all! It is intermittant.

I have done the following after reading a lot of the old archives:
Replaced the OPV
Replaced the fuel pump relay
Replaced the O2 sensor
Set the Lambda to approximately 50%
Replaced the water temperature sensor
Cleaned the ICV with carb cleaner

The problems started about the same time as I replaced the thermostat. Car was extremely slow to warm up. I also had a problem with a fuse when the windshield wipers and front windows won't work. I unplugged and replugged all the ice cube relays and got the electrical function back. Could any of this affect the rough running?

As part of the troubleshooting, when I pull the connector from the ICV, idle jumps up to about 1500. When I unplug the OPV the idle jumps to about 1500. When I unplug the EHA, nothing happens but when I plug it back in the idle drops to 650 and then slowly rises again. I tried pulling the spark plug wires one at a time and could not get any difference. It continues to miss. I also checked all the vacuum lines and sprayed carb cleaner on all the lines and the injectors and got no speed change. Engaging Aircon makes no difference in the roughness.

I have not checked fuel flow or pressure yet. Plugs were new last fall.

I know this is long, but any advise will be persued.
Thanks.

__________________
Nokandolah
88 560 SEL 285,000 miles
82 300SD 126,000
94 Ford Explorer 186,00
07 Hyundai Azera 10,000

A friend with a '87 560SEL experienced similar symptoms a few months ago.

It was the ignition coil.

Duke

in my case, it runs smooth but with hard start at cold and intermittent rough idle particularly in park. I also had a high idle but just resolved it by replacing the ICV. I tried cleaning the ICV but did not work. ICV tested OK as a unit but cannot pull the idle down to where it should be. It stayed at about 1000 in Park/neutral but would drop to 600 in gear. The idle is now 700 in park and 600 in gear.

My O2 sensor tested out of spec, so I have ordered a new one. It should arrive tomorrow. I will then do a re-test after I have installed the O2 sensor.
In my research and consultation with other folks in the Forums, I realized the imprortance in understanding how the process works, in order to tacke a DIY such as this one. The fuel injection system is quite complex but now feel more comfortable after a lot of readings. The testing involves measuring EHA resistance, voltage, and load current. Another test is the on/off ratio. There is a concept called open loop(cold/warm engine) and closed loop(oper temp). Looks like you have done some logical steps in testing/replacing the temp sensor, OVP, etc. The throttle position switch is also one of the variables often discussed.

The clue about the coil is a good one. vacuum leaks is also one that is often discussed. I have looked and looked, but could not find any,

Nokan -

You may also wish to check your Idle Control Unit (found up behind the glove box on my 500SL - not positive about that for the SEL). I had the same symptoms and that was the culprit (lots of posts on this). You wouldn't think so if it is intermittent but it was.

They're several hundred $ - if you know someone with the 117 engine, bribe him/her with a couple of beers to swap/check. Also, get sme Doan's pills or hire a contortionist to get at it for you (LOL).

Good luck
Kevin

I removed the fuel line at the fuel distrbuter and and ran it into a gallon jug. I got about 2 ounces of water! I was trying to check the pump volume and I guess I got lucky. I have added 4 cans of dry gas to 3/4 of a tank of fuel and plan to run it for a few days and see if it gets better. It is better than it was but still not as good as it could be. I only ran it 10 miles.
I'm not sure how the fuel pump works. When I did my test, I turned the key on and the pump ran for about 1-2 seconds and pumped about 2 ounces of fuel and stopped. Every time I cycled the key I got the about 2 ounces. I expected the electric pump to run continuously into the open jug. Do I have a fuel pump problem?
Thanks for the advise on the coil. Sounds logical since I have the problem at idle and highway speed. I think it is the original coil with 265,000 miles so it might be time for a new one if the dry gas doesn't solve my problem. I couldn't find a test in searching the forum. Do I have to just do another remove and replace?
I don't know anyone I can mooch a loaner idle control module from. Does it make it run rough or just affect the idle speed? If I can get it running smooth I can live with a little high idle. If I get that far, I'll consider a new IVC.

This forum is the greatest!

__________________
Nokandolah
88 560 SEL 285,000 miles
82 300SD 126,000
94 Ford Explorer 186,00
07 Hyundai Azera 10,000

After many false paths, I fixed the rough idle and other problems by replacing the coil wire. I bought a new coil but when I started to replace it, I noticed the coil wire was stiff. I re-routed it and my problem was solved. I went ahead and replaced the coil along with a new wire and all is well. I pulled the brass end connectors off the old wire and used a new piece of wire core lead and re-used the old connectors. If I need new plug wires in the future I will replace everything. I suspect that when the plug wires were replaced in the past, the coil wire was not as it is difficult to get the plastic cover off the coil to get access to the plug connection. I learned a lot about the fuel system, idle control, relays etc. so I look at it as paying tuition to be better capable of maintaining the car in the future.
Thanks again for the earlier advice to change the coil as it was the root of the problem.

__________________
Nokandolah
88 560 SEL 285,000 miles
82 300SD 126,000
94 Ford Explorer 186,00
07 Hyundai Azera 10,000