Intermitten high idle 1985 126 380se - PeachParts Mercedes-Benz Forum

earl orchard · #1 06-17-2013, 04:11 PM

Hello All
my 85 380 has a weird high idle problem,the car will start great run at normal idle(about 650 rpm) then after about 5 minutes the idle will climb to 1500 in park/1000(hot or cold engine does not seem to matter) in drive and idle at 1500/1000 for right at 5 minutes,or it might do it for 10 minutes or more,so i tested the ICV(silver tube in front of the engine)and found
high idle_no voltage at the ICV-pulling connector made the idle rise to 1500/1000
normal idle-12 volts at ICV pulling connector raises idle
if i jump 12 volts from the battery to the ICV the idle drops/car dies
i have a print out from what i think is the FSM thats were i got the test from
i didnt do a test at the idle control module(black box on the firewall)
so is my idle control module bad? i put in a new temperature idle switch and cleaned the ICV but that has not changed anything
sorry if this is to long
Kenny

JamesDean · #2 06-17-2013, 04:21 PM

I would test the resistance across the IACV. It might be out of spec.

I'm not recalling if this uses the same idle control system as the late model cars or not...

earl orchard · #3 06-18-2013, 09:31 AM

I checked the ohms at the ICV prongs and got a reading of 10.5

JamesDean · #4 06-18-2013, 09:33 AM

I believe 10 is out of spec, at least for the later systems...I'll have to check over the FSM again and double check

hookedon210s · #5 06-18-2013, 10:26 PM

You need to test the system according to the attachments below. Mark

pmckechnie · #6 06-19-2013, 08:28 AM

Had a problem like that on my 84 500SEL a few years ago. I found there was a bad connection at the idle controller. I found the problem when I removed the mounting screw that holds the controller in place. Pulled it up so I could see the connector (engine still running at the time) and the idle went back down. I held the controller and moved the cable up and down and side to side and the idle would jump up and down. It turned out to be a bad connection in one or more of the contacts in the plug. After trying to clean the contacts without success, I carefully removed the cover for the plug and removed the wires one at a time and squeezed contact with pliers VERY VERY lightly, just enough to close up the gap. You will see gap I am talking about. Just be careful and don't get the wires mixed up. Make yourself a chart of pin number to wire color before you start removing the wires. I haven't had a problem of high idle since.
I have had a problem of LOW idle, but not high idle. That turned out to be the idle valve.

Paul

earl orchard · #7 06-19-2013, 09:27 AM

Thanks for the reply
Was yourhigh idle intermittent? Mine has not gone high idle now since Monday
When I put the problem up on here ...it knew I was talking about it
Kenny

earl orchard · #8 06-19-2013, 09:38 AM

Thanks hookedon210
I have that printed out already and followed the test and according to that I need a new idle control module (black box on the firewall) but it was not clear if they were talking about a high Idle all the time , or like mine does we're it might go a couple of days between normal and high idle.
I guess what iam getting at is that what a idle control module does when it goes out? Flaky erratic idle? Normal for a day or two then high idle city for a couple of days ?
I had a 210 ,killed in a hailstorm last spring.

Kenny

hookedon210s · #9 06-19-2013, 10:53 AM

Yes, it can be intermittent with a faulty idle control computer or bad connections at the plugs. Also, the solder jobs in those days weren't noted for longevity. It may be worth your while to take the cover off of your idle computer and plugs as noted above to look around for bad solder joints to re-solder. In the past, I purchased 2 rebuilt idle computers for my Euro 380SE which worked OK for a time but never really got the idle rate as low as it was supposed to be. I finally gave in and purchased a new OE idle computer and never had another problem with getting the correct idle rate. Mark

JamesDean · #10 06-19-2013, 10:54 AM

For reference here is what the insides of the idle speed controller look like:

http://www.peachparts.com/shopforum/tech-help/339296-inside-box-v8-idle-speed-control-fuel-pump-relay.html

hookedon210s · #11 06-19-2013, 11:01 AM

Yeah, probably not much to do in the 420 computer. IIRC the 380 is different but I have never tried to repair the 380 computer. Mark

pmckechnie · #12 06-19-2013, 11:53 AM

Yes, I had an intermittent fast idle. I had the problem for a couple of years but could not catch it. It finally got bad enough that I was able to track it down. I had changed the valve and the control with used parts and the problem would go away for a while and then come back. Hasn't failed since I cleaned and adjusted the wire connectors in the plug. It's been several years now with no problems.

Paul

earl orchard · #13 09-24-2013, 04:02 PM

i bought a rebuilt idle control module and installed it a week ago and there is no sign of the weird high idle, looks like that did the trick, car runs great now
thanks to all that helped with this!

cheers

kenny