Idle Surge

[bazzman]

Hi All

My 1986 230TE has developed an irregular idle.
It's not very bad, just floats up and down by say 200rpm every 10 seconds or so.
In itself, it's not a real issue, but it's a dry Saturday morning, -makes a change - so I thought I'd check it out.

I've recently done plugs, airfilter, and the plug leads are 18months old, so I thought I'd check the OVP. Sure enough the connector pins were a bit corroded. I thought I would check inside, and it looked fine. Quite dry and seems free of broken solder joints.
BUT, I tried starting the car without the OVP and it starts and idles totally smoothly.
It would seem that somehow the OVP is faulty, but before I spend £50 on a new one, can anyone tell me why the car should run better without the OVP?
I thought the OVP was basically a fuse. Worked or it didn't.
Am I wrong?
Should I just leave the OVP out?

Cheers

 

[ba9rn]

See also: http://www.carelect.demon.co.uk/merc.html

 

[bazzman]

Thanks for the info, but, if the car runs so well without the OVP, can't I just leave it out?

Cheers

 

[television]

I am thinking is the wiring correct on the car, the engine ECU and ABS ECU all draw from the OPR, the idea being that any serge protects these expensive units, in my view the OVR has been bridged, and that the OVR is faulty, dragging down the 12 volt supply as it is giving the symptons of a faulty OVR.

Pin 30 is the input and has 12 volt, any pins 87 are the output, working should be 12v, nothing with it unplugged, and 7.5 volt in the fault condition.

malcolm

 

[bazzman]

Television:
Thank you , I appreciate your input.

As far as I know, the car is standard, and the wiring all under the bonnet looks 100% normal.
From your comments I need to keep the relay in, the ABS light comes on if I remove it anyway.

I'll buy a new one, the date stamp on it is 1986, so from other people's comments that these units only last max 100k miles or ~7-10 years, I should change this anyway as my car has done 176k miles so far and has just celebrated its 20th birthday!

 

[television]

Television:
Thank you , I appreciate your input.

As far as I know, the car is standard, and the wiring all under the bonnet looks 100% normal.
From your comments I need to keep the relay in, the ABS light comes on if I remove it anyway.

I'll buy a new one, the date stamp on it is 1986, so from other people's comments that these units only last max 100k miles or ~7-10 years, I should change this anyway as my car has done 176k miles so far and has just celebrated its 20th birthday!

Like wine, 1986 was a good year for them,1991-95 were bad years is the fuse on top OK, hard to tell people to buy something, but the symptons say that it has gone.

Malcolm

Malcolm

 

[bazzman]

Hi Television

The fuse on top is fine, if I remove it the ABS light comes on, but I checked it with a meter anyway!

Cheers

 

[G MAN]

http://www.carelect.demon.co.uk/merc.html


Mercedes Common ECU Failures

ALL MERCEDES MODELS - Intermittent poor/non start or poor idle/running. Has vehicle got overvoltage protection relay (also called OVP relay or surge protection relay)? If yes REPLACE! any problems here can cause fuel injection system mis-operation.



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Late type SLK (from 1999) and new C class (from 2002) suffer from 'check engine' light illuminating with PO30/32 codes (misfire). This is caused by defective soldered spur connection in wiring harness (+12V feed to coils). Resolder to rectify.

HI MALCOLM , G MAN AGAIN, would this info. from the link above by ba9rn be applicable to my problems with poor running and if so would you know where exactly is the spur connection that is referred to?

Also looked to check for any fault with my OVP fuse/relay but couldn't figure out which one of four plug in relays it could be under a cover behind the main fusebox. Am I barking up the wrong tree?

 

[bazzman]

Hi All

I thought I'd provide a report to finish this thread. (Don't you just hate it when people start threads talking about problems you have on your car, and you never find out what happened??)

Anyhow, new OVP, for my 1986 230TE Part 201 540 08 45.

Idle problem totally sorted. She (my car's definitely a female - don't ask me why I think so) idles and runs really well, especially for such an old girl.

Anyway, thanks to all of you who advised me.
Cheers

 

[G MAN]

Good result, always worth asking as there are people on here who know & are knowledgeable or have had similar experiences. Happy motoring!!