1700 RPM IDLE ANY IDEAS - PeachParts Mercedes-Benz Forum

Jimbenz85 · #1 11-22-2009, 01:35 PM

HELLO, I have a 1985 380 SE the idle is racing at 1700 rpms do you know what it is also where is the OVP RELAY located thanks

professor · #2 11-22-2009, 01:43 PM

Does yours have ABS? If so, is the light on?
When the OVP fails the RPM does tend to go up. If it's anything like my 560SEL, the OVP in inside the firewall in the center. It will have a clear plastic cover where you can see a 10A fuse in it (sometimes a dual fuse).

will look like this

Jimbenz85 · #3 11-22-2009, 01:51 PM

yes ABS light is on thanks will look for relay

brandlj · #4 11-22-2009, 01:52 PM

On a 85 380se, the OVP relay is in the fusebox. Has a red fuse on top 10Amp

quaid · #5 11-22-2009, 03:32 PM

When my 500SEL had a high idle, it turned out to be the idle control unit behind the instrument cluster. My ABS light wasn't on all of the time though.

PanzerSD · #6 11-22-2009, 04:25 PM

Quote:

Originally Posted by professor

Does yours have ABS? If so, is the light on?
When the OVP fails the RPM does tend to go up. If it's anything like my 560SEL, the OVP in inside the firewall in the center. It will have a clear plastic cover where you can see a 10A fuse in it (sometimes a dual fuse).

How does the failure of this ABS system relay effect engine function to the point of a 1700RPM idle?

professor · #7 11-22-2009, 04:37 PM

Quote:

Originally Posted by PanzerSD

How does the failure of this ABS system relay effect engine function to the point of a 1700RPM idle?

It's actually the other way around. The OVP is an Over Voltage Relay, when it fails two things will happen, the car is hard to start and the idle would go crazy high. Once the idle shoots up the ABS warning light comes on to tell you that your ABS system will not be on when you need it. Now this is my opinion but I had the exact same situation and the problem went away for ever after I replaced the OVP (not just the fuse). Inside the OVP there is a Zener diode that's suppose to regulate the voltage that feeds the CIS system, so if it is shot then I have a feeling it sends a signal to the ICV (Idle Control Valve) to compensate which will most likely kick in the high idle. My 2 cents!

PanzerSD · #8 11-22-2009, 05:33 PM

Makes sense to me!

PanzerSD · #9 11-22-2009, 05:34 PM

Tell me, The electronic ICV, is it a variable voltage thing or is it on or off(open close)?

professor · #10 11-22-2009, 08:39 PM

Quote:

Originally Posted by PanzerSD

Tell me, The electronic ICV, is it a variable voltage thing or is it on or off(open close)?

Actually I saw the darn thing open and close gradually based on some current feed or voltage variation I assume. I held one in my hand while it was plugged in and watched as the air meter flap was hunting up and down at idle for a balance.
I think at start it opens completely as the cold start valve is injecting. Just observation mind you, so I am not sure what the real design calls for.

raymr · #11 11-22-2009, 09:23 PM

This can happen if the idle control unit gets disconnected or goes bad. The default idle speed is then ~1700. It is a plastic box located in the firewall behind the air cleaner. The connector is on the bottom. Check that first.

ctaylor738 · #12 11-23-2009, 12:58 PM

The power to the ABS, the idle control unit, and the lambda control unit is regulated by the xener diode in the OVP. The OVP itself is protected by the fuse on top of it. So if the fuse is bad or the OVP goes TU, all of these control units shut down. The ABS turns the light on, the idle control valve sits at open all the time which makes for a high idle.

The ICV is actually a frequency valve. The ICU adjusts the frequency that it closes to regulate the air to maintain a certain idle speed. But you can measure the output of the ICU in volts by sliding the connector back a bit and touching the probes carefully to the pins.

raymr · #13 11-23-2009, 01:16 PM

OOps, missed the reply about the ABS light.

ddayme · #14 11-23-2009, 01:22 PM

I have been having high idle issues for over a week, and I think I have it narrowed down to the OVP, as when i remove it/wiggle it/tap on it while installed, the problem goes away, but it is still intermittent, so a zener diod going bad makes sense, I'm sure this diode can be removed/replaced.

professor · #15 11-23-2009, 04:45 PM

Quote:

Originally Posted by ddayme

I have been having high idle issues for over a week, and I think I have it narrowed down to the OVP, as when i remove it/wiggle it/tap on it while installed, the problem goes away, but it is still intermittent, so a zener diod going bad makes sense, I'm sure this diode can be removed/replaced.

In your case it sounds like you have a loose or bad connectivity. You can open the OVP case and solder any cold or cracked spots. Also make sure your OVP is well seated.