82 380 SL - Surging Idle - PeachParts Mercedes-Benz Forum

ArborWrench · #1 07-17-2012, 05:01 PM

So I've been troubleshooting this for a couple weeks now. I have a surging idle when the car is parked and sometimes it dies. The car drives great and has plenty of power, but when idling is will commonly surge up and down. I started troubleshooting this as a vaccuum leak and I found a couple cracked hoses and one hose disconnected which I've resolved. Still have the issue although slightly better. Next I cleaned the Idle Control Valve thoroughly and checked operation by applying 12 volt to the valve. Works great. Now what? So I pulled the 40 degree temp sensor and jumpered it and this seemed to resovle it. Drove it for a day and the issue comes back as before. I experimented with this temp sensor plug pulled, jumpered and on the sensor and still have the idle issue. So now I'm thinking it could be a the Idle Control Unit. I pulled the board and inspected it with no obvious cracks, burnt resistors or anything else like that. Also pulled the Overload relay and tested it for operation and the relay works fine and the diode seems to work fine. Relay works, diode seems to work.

My question is this: is there any bench testing method for the Idle Control Unit? Could this also be the warm up compensator? Is there a bench testing method to ensure proper operation of that?

meltedpanda · #2 07-18-2012, 11:15 AM

http://www.peachparts.com/shopforum/sl-forum/233241-380-sl-idle-oscillates-between-500-750-rpms.html or http://www.peachparts.com/shopforum/sl-forum/273277-voltage-icv.html
may help

air and fuel - the two ingrediants to a lopeing idle , gotta check everything that controls those two factors

ArborWrench · #3 07-18-2012, 12:44 PM

Thanks meltedpanda. I read the first post you linked before I posted and went through the same procedure to no avail. The second post is interesting and I'll have to check my voltages tonight. I know I was only getting 5 volts at the Idle Control Valve when I last checked it, so that seems low. It does function on 12 when I tested it and the idle jumps up to a steady 1100 if I pull the connector off the ICV.

Where in the manual do they show a test procedure for the electronics? I can't find that anywhere.

ArborWrench · #4 07-18-2012, 12:55 PM

Nevermind- I found the electronic idle test procedure, I'm just not getting 12 volts.

Is there a test procedure for the overload relay?

meltedpanda · #5 07-18-2012, 02:42 PM

not sure , I always just replaced the "cubes "

ArborWrench · #6 07-18-2012, 03:51 PM

Well I think I solved it! (knock on wood) At lunch I picked up a new ICU. I was checking the part number to make sure they matched and they didn't, did some research and called the remanufacturer Programma and sure enough the old ICU was for an 83-85 NOT my 82. Plugged it in and got a rock steady idle at 750. Niiiice.

I'll update later assuming this was indeed the fix.

meltedpanda · #7 07-18-2012, 04:03 PM

Where does one just "pick up" an 1982 ICU. Haha

ArborWrench · #8 07-18-2012, 04:18 PM

I've got a great machine shop in Seattle that can always find the right parts and get them quickly- Autosport Seattle. They are awesome. There was actually an Aston Martin DB2 in there last time I was in. Beautiful car.

jim16671836 · #9 07-25-2012, 10:43 PM

I am messing with a 1984-380SL. Do you have the part number for a 1984 and is your idle control unit still good. Where is it located on the SL's. thanks