Tickover "hunting"

[Two Bags]

My E320 cabrio 1993 has started to "hunt" on tickover. It races up and down between 6-900 rpm. Then, for no reason it will stop. Today though it seems worse. I'm told this is electrics? but difficult to sometimes cure. Any ideas please!

Thanks

 

[grober]

Could be lambda sensor,or idle control valve, or inlet manifold leak, or dodgy plugs, or several other things. Best hooking it up to an engine analyser to narrow it down a bit.

 

[Two Bags]

I understand that you can't on this model.....

 

[PJH]

Twin Cam Engine, right ? Check the wire for the inlet cam idle settings. It's under the plastic cover at the front of the engine.

 

[janner]

There are so many things it could be you need to first read the fault codes.
This explains how to build a reader.
Read the codes, clear them all, run for a while (maybe even a few days) then read them again.
If you get lots of odd codes you may have a wiring harness fault or a faulty throttle body (wiring again).
If the codes don't help then if could be a vacuum leak, faulty coil or dirt on the throttle plate.

 

[KLP 92]

I would check 2 thing on this car. Firstly clean the throttle body assembly and secondly try changing the MAS sensor.

 

[Parrot of Doom]

My TVR used to do this, it was an air leak on the plenum.

 

[grober]

Older Type Analyser

I understand that you can't on this model.....

I meant the the old fashioned type of analyser described by VLAD in this THREAD. Lots of garages have them, but they are only as good as the person operating them of course. They dont display fault codes but rather ignition "firing lines" which tell a lot about whats going on in the cylinders/ ignition-timing etc. They also have an exhaust gas analyser facility which gives info on mixture /combustion. http://mbclub.co.uk/forums/showthread.php?t=31053 and as Janner says you can get some fault codes from the diagnostic socket.

 

[Vlad]

If you do a search under OVP or some of my very old posts you should find the answer to your solution.....the problem you describe is a common ailment of the M104 2.8 and 3.2 engine.

Hope this helps.

 

[television]

Yes should be the OVP relay, this was a bad year for them, due to poor soldering. You can check it out with a meter, 12volt in on pin 30 should be 12volt on the outputs pins 87, you also have a fuse on top.
Start the car up and give it a clout, if the revs change you can solder up or by a new one.

Malcolm