Tickover "hunting"

[Paul Tuohy]

My E320 cabrio 1993 has started to "hunt" on tickover. It races up and down between 6-9000rpm. 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

 

[kth286]

Paul

The lambda sensor in the exhaust system is considered a service item to be replaced approaching 100k miles. This item provides feedback to the computer which then injects the correct amount of fuel into the cylinders by altering the time the injectors stay open. If it is not working properly the feedback will be all over the place.

Another service item that often gets missed is the replacement of the charcoal canister in the wing. This can get blocked and cause driveability problems and even collapse of the fuel tank.

BUT, first get the codes read by someone that understands Mercs of this vintage, as there are obviously other areas of the engine management system that could be causing this problem, an obvious one being a tear in a hardened vacuum line letting in air.

 

[television]

My E320 cabrio 1993 has started to "hunt" on tickover. It races up and down between 6-9000rpm. 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

It should be the OVP relay, this was a bad year for them, they have many soldering problems, do check the fuse on top. either re solder if faulty.

Should be 12 volt on the input pin 30 and 12v on the output pins 87.

malcolm

 

[Paul Tuohy]

I'm having the car picked up at the weekend by a Merc Specialist. He immediately plumped for the OVP relay - is this expensive? I presume their could be other reasons that will have to be checked ...what about the coils? Would they cause this problem? thanks for this feedback so quick!

 

[Paul Tuohy]

David,

Your thoughts are very interesting and something not yet mentioned to me. I will pass on to my Merc man to see if if these can be checked.

 

[television]

The OVP relay cost around £50 and you can plug it in your self.

Malcolm

 

[Stevie A]

My E320 cabrio 1993 has started to "hunt" on tickover. It races up and down between 6-9000rpm. 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

Is it a Maclaren Mercedes Formula One car you have Paul? 9000 revs eh. Sorry, I couldn't resist.

Otherwise, I agree with what Malcolm has said totally.

 

[Paul Tuohy]

Thanks Steve! I did of course mean 6-900rpm.....