1995 W124 E280 - what should the idle speed be??

[howeshouse]

Sorry to have to ask such a basic question! The car has just been failed with "idle speed too high" and "CO emissions too high". Before I go and spend the money to have a diagnostic test done, I just wanted to query the idle speed as I certainly hadn't noticed any change in that since last year: it holds steady at around 700 rpm. Thanks, Adrian

 

[eric242340]

Sorry to have to ask such a basic question! The car has just been failed with "idle speed too high" and "CO emissions too high". Before I go and spend the money to have a diagnostic test done, I just wanted to query the idle speed as I certainly hadn't noticed any change in that since last year: it holds steady at around 700 rpm. Thanks, Adrian

Idle speed sounds correct, but your CO level could be too high, have the fuel system serviced. The idle speed, if 700 rpm, is not too high.

 

[Suki]

if it requires adjustment (big if!) I beleive you use an allen key in a hole in the casing of the air filter.

 

[Bolide]

Is the failure gross or marginal? If marginal the normal technique is to test the car hot following an Italian Tune-up

Nick Froome
www.w124.co.uk

 

[kth286]

There is no adjustment on that engine it is all electronic. The lambda sensor in the exhaust pipe has probably gone.

Usually considered a service item at around 100k miles, as they lose their effectiveness.

Give your VIN number to the parts dept to ensure getting the correct one.

The idle speed is slightly high (is the car an auto?) and may be due to the engine coolant sensor getting old. This sensor is critical to engine performance parameters and for the sake of something like £14 is advisable to change.

AS previous poster mentions, always drive the long way to the service station for an MOT to get the engine fully up to max temperature when emissions are at their lowest.

 

[television]

There is no adjustment on that engine it is all electronic. The lambda sensor in the exhaust pipe has probably gone.

Usually considered a service item at around 100k miles, as they lose their effectiveness.

Give your VIN number to the parts dept to ensure getting the correct one.

The idle speed is slightly high (is the car an auto?) and may be due to the engine coolant sensor getting old. This sensor is critical to engine performance parameters and for the sake of something like £14 is advisable to change.

AS previous poster mentions, always drive the long way to the service station for an MOT to get the engine fully up to max temperature when emissions are at their lowest.

Would the sump breather affect this,mine failed in Sweden before I could speak or read Swedish, they point to and told me to go home and clean it.

malcolm

 

[howeshouse]

Took the car to the MB main dealer in Harrogate to have the diagnostic test done. Result - everything checked out as normal: idle speeds, CO, lambda... going back to the original MOT station with the printout for their comments!

 

[television]

Took the car to the MB main dealer in Harrogate to have the diagnostic test done. Result - everything checked out as normal: idle speeds, CO, lambda... going back to the original MOT station with the printout for their comments!

As Nick said could this have been due to the temperature of the engine.

If your MOT station is only local the engine could have been too cold at the first test.

124s run on the low side at around 80c and all are border line getting through the test.
What Nick means is that it best to lock up into 3 on the shift and give the car a fast run. In Sweden the MOT testers did that first in winter.

Malcolm