Lumpy Idle On My W124 320CE

[daclick]

The expertise of this board on this issue would be greatly appreciated.

My 1993 320CE with 115,000 miles has developed a lumpy idle, this happens when the car is hot and makes for quite jerky reversing. I think fuel consumption may have taken a slight hit as well.

The tacho dances from around 700 - 900 rpm when this happens which I reckon is about 50% of the time the car is idling.

I should point out this car is in the UK with a catalytic converter and the 'modular' (if that's the right word) ignition system with 3 coils.

So far the air mass sensor has been replaced, along with some of the old, biodegradeable wiring and the OVP relay.

I also make a habit of cleaning out the throttle body, butterfly and air intakes. I used smoking pipe cleaners to get all the dirt out of the idle ports down there until they were sparkly clean - you could eat your dinner off my throttle plate hehe.

Service parts such as spark plugs and the air filter have also been changed.

IMHO the erratic nature of this problem makes me think its a fuel issue, I'd be happy to take on any ideas though.

All input welcome.

 

[kth286]

It could be one of the coil packs and that is the result of shorting engine wiring loom.

I would not trust an engine wire loom which has been patched. Bite the bullet and replace the loom.

Other items are:

Coolant temp sensor, cheap, and they do go out of spec. Very important input to the ECU.

Lambda probe in exhaust, and considered a replacement item at 100k miles on our generation cars.

 

[daclick]

Thanks for that.

I have found that the erratic idle goes away when shifting to neutral or park.

Maybe this is due to the revs rising but I tried it a few times today and every time the revs flattened out.

 

[donlon72]

I've got this exact problem, my first thought was "idle control valve" but couldn't even find it!, every time I pull up now the engine stalls, as if the gearbox/clutch isn't disengaging quickly enough.

It seems that when I add the extra drag from the gearbox by putting it in gear it affects the idle dramatically, even enough to stall the engine, could this be some sort of inhibitor switch in the gearbox itself?

I'm guessing here but I would have thought that there is some sort of switch to tell the ECU that the engine needs more revs/fuel/air to withstand the extra drag created by the gearbox when it is in gear and that maybe this isn't working?

Anyhelp would be greatly appreciated.

 

[mattkh]

I've got this exact problem, my first thought was "idle control valve" but couldn't even find it!, Anyhelp would be greatly appreciated.

Hi
Can you put a up a picture, a birds eye view, of your engine

 

[donlon72]

Hi Mattkh, hope this is ok

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Should possibly mention that this also seems to stabilize when in neutral or park.
Cheers Rich.

 

[donlon72]

Sorry also forgot to mention this, my car is a '93 E320 cabriolet, airbag model.
Cheers Rich.

 

[dvm]

Hi DACLICK
I posted a lumpy idle yesterday. I have had a conversation with the main agent again and their solution was that lots of cars that come to them do either short trips or the trips are done at low revs with the outcome that lots of engines are not worked enough causing the valve stems to become gummed or a deposit to form and build up on the valve which eventually causes the valve not to shut completely. Their answer is they take the car on the motorway and do 4,500 revs in 3rd gear for 10 to 20 miles and if there is no change in condition then they start looking at other things. I don't know if this matches your symptoms or not but thought I would pass it on.

 

[kth286]

In addition to the items (coolant temp sensor and lambda probe in exhaust) in my previous post above, I should have included the charcoal canister in the nearside wing which is part of the closed circuit fuel tank emissions system. The charcoal canister is listed in the service schedule as a replacement item every 72,000 miles and this can get clogged and affect driveability

I have replaced all three items, and my car engine performs faultlessly with perfect idle in all condions and with 156,000 miles now.

I do all my own servicing by the book.

The throttle body butterfly intake has never been cleaned, and I do not believe that is the main issue with our cars when people mention it. Cleaning it just gives some slight temporary relief to the main issue which is elsewhere.

There is no seperate idle control valve on our engines, the idle control is all done electronically.

 

[donlon72]

In addition to the items (coolant temp sensor and lambda probe in exhaust) in my previous post above, I should have included the charcoal canister in the nearside wing which is part of the closed circuit fuel tank emissions system. The charcoal canister is listed in the service schedule as a replacement item every 72,000 miles and this can get clogged and affect driveability

I have replaced all three items, and my car engine performs faultlessly with perfect idle in all condions and with 156,000 miles now.

I do all my own servicing by the book.

The throttle body butterfly intake has never been cleaned, and I do not believe that is the main issue with our cars when people mention it. Cleaning it just gives some slight temporary relief to the main issue which is elsewhere.

There is no seperate idle control valve on our engines, the idle control is all done electronically.

Thanks, this post has helped me make a decision to change the lambda probe, might possibly put a new exhaust on as the old one is starting to sound a bit rough.

 

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