Uneven Idle

[porker]

I have a 1993 E280. When the engine is warm and the footbrake applied, the vehicle stationary and in gear, the revs rise and fall. If the footbrake is released in order 'creep' forward the whole process is not very smooth as the revs rise and fall. However on tickover in neutral the engine is fairlt smooth.
Any thoughts...

 

[talbir]

Sounds like a faulty Crank position sensor or OVP relay.

 

[vic condon]

I had the same problem on my e280 (straight 6), there is a butterfly valve on the inlet manifold that can break up, and cause said problem.

 

[porker]

e280 Idle

I have just come back to the problem with the idle. It seems to be surging during warm up after about 10 mins driving. Once the engine is at operating temp all is OK. I removed the OVP relay but could not find a way of getting at the contacts. The ABS warning light extinguishes once the engine has started. Where is the butterfly valve on the inlet manifold so that I can check it?

 

[mjtray]

Porker,

Yeah, it sounds like we have similar problems, although I think my very low idle has something to do with it. Your E280 problems sound just like my exE280. Most of the surging on that car was caused by the throttle body being dirty and a duff OVP relay. Inside the throttle body you have a butterfly flap that tends to attract a load of crud on its edges, where it seals against the throttle body. Once this was cleaned off it ran better but was not cured.....this is an easy job to do. As you look at the engine follow the air intake tubes from the air cleaner, across the engine and where it then drops into the metal throttle body. Just undo the jubillie clip and pull the plastic tube off the top of the throttle body and have a look inside......you will see what I mean.

Secondly the OVP relays do go bad.....the originals had a design flaw which caused the internal soldering to break down. If yours is the orginal and has Made in Austria on it then I would advise getting it changed. Costs about £45 to purchase and is a 10 minute replacement once you have moved the battery.

Thirdly as you look at the engine there is a valve that sits on the right hand inner wing by your ABS gubbins. This valve has two rubber tubes going into it and is held on by two bolts. I think its called the ReGen valve and apparently it getts all carboned up. Costs about £50 and is really easy to replace.

I have also heard that the butterfly valve in the square black box that sits between the intake manifolds....it has four bolts on the top, can break up. May be worth having a check inside to see what it looks like. I think I may also have a look on mine.

I'll be interested to see how you get on.

 

[porker]

mjtray
Many thanks for the detail I know what I'll be doing at the weekend. I'll report back in due course.

 

[porker]

I checked the OVP relay and appears to made in Germany. The ABS is all working so assumed this would be OK as it is tied in with the OVP relay. I then cleaned the throttle butterfly and the butterfly valve. These all seemed fine, and made no difference to the problem.
When the engine was actually throttle surging I disconnected the engine side pipe from the regen. valve. When I put my finger over the end against the vacuum the problem disappeared.
This led me to believe that the regen valve was faulty. The price from the local dealer £61.84 plus VAT.
I thought that it would be worth a closer look at the valve. When I removed it and connected it to 12v supply there was a very faint click. I unclipped the bottom of the valve and removed the diaphragm. I could see that the piston was moving when 12v applied but not returning. A squirt of WD40 and it operated more positively. Refitted to the car and the surging problem has diappeared!
Hope this helps others in the same situation and saves them £73.00 :lol:

 

[guydewdney]

this valve - is it the exhaust re-circulation valve, or 'electric change over valve' (almost perfectly cube shaped, with two screws holding it on)

i'd like to check the same one on mine, but my V8 is a bit more complex...

tia

guy

 

[porker]

I believe it's called the air regeneration valve Part No 0004702193.
It has an air tube feeding into one side and then another exactly opposite going to the engine. On the top is a two pin connector and MOT with an arow printed on the top of the body. Presumably MOT means motor as this arrow points in the direction of the tube to the motor.
It is mounted on a rubber mount that push fits onto a bracket on the inner nearside wing.
Maybe a call to MB with the part number will reveal its proper title...