At wit's end over an idle issue - PeachParts Mercedes-Benz Forum

troylatif · #1 12-17-2008, 04:26 PM

Hi all,

This post is to follow up on a previous post I created to discuss an idle issue I'm having with my 1985 380se. I've been through a lot of work in dealing with the problem and I'll list it out with steps that I've taken.

- I've tested the throttle position switch in the throttle wide open position and the throttle shut position. Both close the continuity tester.

- I've found a blown resistor in the Idle Control Unit. I've replaced it twice with no luck. The idle still rides high.

- I've replaced the idle control valve. I tested the old one; it bounces up and down between 32 and 50 ohms. The one I received sits well at 5 ohms.

- I've tested the voltage across the nos. 2 and 4 pins on the Idle Control Unit connector. I get a solid 12 volts.

- I had my parts supplier send me another control unit because the first I suspected of being shot and to no avail, the one he sent also had no effect.

Could it be a vacuum leak somewhere? Could it be to do with the switchover valve; the one on top of the driver's side fender under the hood.

I tell you, this problem is such a mystery. It started randomly one morning when I was driving out to work. I momentarily pressed the gas and I felt a sudden jump in power and since then the idle's been running at about 1600 - 1700 cold and between 2000 and 2300 warm.

I've almost considered just playing with the timing to get it to come back to normal, but I think that'd really mess with fuel economy. So far it makes between 16 and 17 city and 18 to 20 highway. I used to get 19 city consistently when I came out to Texas. Before coming out here I used to get anywhere between 22 and 25 mpg in the Arizona desert.

I appreciate any insight you guys can provide.

-Troy

RichardM98 · #2 12-17-2008, 04:33 PM

Are you totally against taking it to a dealer and having them hook up the Star diagnostics computer??

It's what I'd do before throwing any more parts at the problem.

Good luck, Troy.

troylatif · #3 12-17-2008, 05:02 PM

I would but they'll run me 100 bucks to tell me something I already know. Such as, replace the unit and valve together with OEM stuff. I once took another car to a dealer just to have them plug it in and tell me it needed a tune-up. The other problem with going to a dealer is they can tell you anything and you just can't put your $0.02 in.

I'm really hoping somebody's had a similar experience, or they know of another system in the car that could have the same described effect.

-Troy

S-Class Guru · #4 12-17-2008, 06:41 PM

Troy, are you close to Dallas?
If so, you should go see David Poole.
He's a wizard with the 126's, and has all the equipment.
He also is One-of-Us here on the Forum.

DG

mpolli · #5 12-17-2008, 09:44 PM

What is your skill level? If low then either you need to study up on the system or get some professional help. I would approach it this way: For the engine to run, air has to go in it. If idleing high then too much air is going in it. For 2000 RPM that is a good amount of extra air. You need to know all the ways air can go in. I don't know that engine/EFI system but generally there is: The throttle, the idle control valve, some emmissions lines such as gas vapors and PCV and EGR, that all lead into the throttle body, and some vacuum lines of course.

You need to try to plug up each of these one by one to see if it is the culprit. For example, you can see if there is a way to make sure the ICV is closed or just plug up the passage way if possible (again I have no knowledge of that engine). Then if it still idles high you can then eliminate the idle control system. If it doesn't idle high then you have found the trouble.

Yes there could be a vacuum leak. I think some times people spray Gumout around to see if the idle is affected. The idea being if it gets sucked in a hole then the idle will change.

Arthur Dalton · #6 12-17-2008, 11:21 PM

ABS lamp ON ??????????

pawoSD · #7 12-17-2008, 11:42 PM

I'd just let the dealer or a good shop deal with it if you've exhausted what you think you can do.

mpolli · #8 12-18-2008, 01:00 AM

Quote:

Originally Posted by Arthur Dalton

ABS lamp ON ??????????

What is your angle? Did they even have ABS in 1985? What would that have to do with the idle speed? I'm not saying you are wrong. Just that I don't have a clue.

pawoSD · #9 12-18-2008, 08:03 AM

Quote:

Originally Posted by mpolli

What is your angle? Did they even have ABS in 1985? What would that have to do with the idle speed? I'm not saying you are wrong. Just that I don't have a clue.

In many cars the ABS/Idle control are part of the same control unit....and yes, ABS was an option even back then.

Arthur Dalton · #10 12-18-2008, 09:13 AM

<>

Yes, you don't have a clue...
ABS lamp coupled with high idle is classic OVP relay failure..that's my Angle....

It's called Diagnostics ....

OVP is power feed for both, so it is First suspect if his condition is coupled w/ABS lamp.

http://catalog.peachparts.com/ShopByVehicle.epc?q=&yearid=1985@@1985&makeid=63@@MERCEDES%2DBENZ@@63&modelid=6246@@380SE&catid=241959@@Body+Electrical&subcatid=241967@@Fusebox+and+Relay&applicationid=P:242003&mode=PA

troylatif · #11 12-19-2008, 11:33 PM

All:

Thanks for the thoughtful responses. I would say my skill level is particularly up there. Its just that with the V in the V8 models, its hard to really track things down without tearing things down to some extent (I'm so particularly against that because I'm pretty far away from my tools here in sunny Tucson, AZ).

My car is currently parked at Houston International.

I've looked at the various vacuum points. I can't seem to find a vacuum leak. Granted, to be effective I really should look at getting a vacuum gun and plug it in at various spots and try to take a vacuum but, yah.

Bingo! It did at one point have an ABS issue. I was doing intensive suspension work and in the process I broke the front right ABS sensor. Now, since then I've been a good owner and I attained a new sensor and installed it. But you've reminded me that around that time I was experiencing strange idle problems but only momentarily. Could this somehow be related? You mention the OVP relay, but I've tested that particular unit and it seems to function just fine. Also, the ICU gets power at pins 2 and 4. I can't quite seem to understand why the ICU isn't processing signals and sending power at some frequency to the ICV. It boggles the mind. Truly, it does.

Well, I'm currently in Tucson and I probably won't be able to get my hands on it until the fifth or sixth of next year.

Hmm... David Poole. I'll definitely look him up. My brother works in Dallas and I visit him on occasion. Does anyone have an email he responds too. I'd sure like to start an email conversation with him before just showing up at his door with my car parked out front

.

Best regards to all of you and a Merry Christmas,

-Troy

troylatif · #12 12-19-2008, 11:35 PM

Oh, and to clarify. The ABS light is not on. It used to be, which was one of the reasons for me to suspect the cracked magnetic tip on the front right ABS sensor.

-Troy

Texholdem · #13 12-20-2008, 12:09 AM

Quote:

Originally Posted by troylatif

All:
Hmm... David Poole. I'll definitely look him up. My brother works in Dallas and I visit him on occasion. Does anyone have an email he responds too. I'd sure like to start an email conversation with him before just showing up at his door with my car parked out front

.

Best regards to all of you and a Merry Christmas,

-Troy

David S Poole
European Performance
10920 Indian Trail suite 101
Dallas, TX
4696880422

Click on
http://www.peachparts.com/shopforum/search.php?searchid=3502376

you can see his posts then by clicking on his name you can send him a message or email.

tan man · #14 12-20-2008, 09:24 AM

Although mine is an SL, its a 1985 and the same 380 engine so I assume common parts.
I am having intemittent idle problem creeping up from 900 to 1200 in Nuetral.
I tested the warm up slide valve by applying 12V and found it was operating so I went on to Idle control module.
I took off the cover and flexed the board which made the idle settle right down. Since I have no soldering skills I replaced the unit with a rebuilt Programa. Worked great for about a week then problem came back so I had Programa swap it for another unit. Same result, good for a few days then problem returned.
Next in line is the OVP, checked and the fuse was ok. I figured its not a fotune for the part and my ABS light was on (I'll go into that later) so maybe the OVP would fix both issues. Replaced OVP, problem still there.

I now strongly suspect the problem is the wiring/connectors to the ICM. Car is bundled up for the winter so I'll have to wait till end March to confirm. I've had problems with those type of connectors elsewhere in the car where you get problem symptoms and its all because of that connector. Jiggle it and they go away. Then the fun part is trying to locate exact point that is loose/faulty.

Regarding ABS light, I didn't suspect OVP because the ABS module was doing its job - at engine start up light would not be on. Once I hit 8-11 MPH the light would go on. I cleaned the 2 front wheel magnetic sensor tips which didn't fix it. Also raised the back wheels and got them up to 20MPH - did not trigger the ABS light. So it must be one of the front sensors. Tested resistance of those sensors and just can't get a consistent reading on those guys. I think the proper test involves giving the front wheels a spin and then testing the resistance, it should fluctuate with wheel speed.

troylatif · #15 12-21-2008, 05:15 PM

Hmm... a loose connector. Come to think of it, the unit was electric taped to the connector. It was particularly tight. However, it seemed as though when I removed the electric tape, it came free without issues.

In all honesty, I bought this car well before I knew anything about cars, electronics, physics, science, etc... I've been finding things in this car that have been jimmy-rigged. When I get back to it in Houston, I'll definitely try flexing the board and pressing on the connector, or just jiggling the wiring leading up to the ICU.

However, this I find strange. What explains the burnt resistor on the original ICU? I look at that particular part and I think, did the OVP not do its job? Could there have been fouling on the fuse that allowed it to pass more current than intended? So far I've acquired two more idle control units and I don't quite see an issue with either, but they don't solve the problem.

Well, first things first, the wiring and the connector along with soldering points on the board.

Thanks to all of you for your input and I'll definitely shoot Mr. Poole a message.

-Troy