Real posser here.

[Ian B Walker]

Working on an E220 saloon (W124) M111.960 engine. The car sometimes surges whilst driving to 2000 rpm. It also, at times dies when coming to a stand still. Engine temp never got above 60 degrees. I first thought Fuel pressure regulator, changed that. Still the same. Got the Throttle body (new fitted by customer) boot strapped by Merc in Preston. Still no change. Changed the temp sensor, thermostat and OVP Relay (all new). Still no change. However the engine now runs at 80 degrees and is comfortable. No Vacuum leaks and fuel pressure at 5 bar (this is ok as I compared it with another car of the same age and model number). Still doing the same. I am sadly at a loss as to what the root cause is. Anyone able to shed some light before I go hitting my head against various solid objects?

 

[Dieselman]

Check the crank sensor and fuel distributor setup.

 

[Ian B Walker]

Thanks Will. Fuel distribution system?, its electronic. No Fuel distributor.

 

[Mudster]

My wife had a Vectra that had the same symptoms, it was actually a common problem on these, was usually either the crank sensor or the cam sensor, or both.

I know it's a different car but it kind of ties in with dieselmans suggestion too.

Certainly worth a look if you're scratching your head.

 

[Dieselman]

Any noises, spitting, backfiring.?

Once it starts doing this does it continue or go away again.?

 

[Ian B Walker]

Any noises, spitting, backfiring.? No

Once it starts doing this does it continue or go away again.? Goes away again

......

 

[Dieselman]

Is the fuel pressure under full load maintained Ok.? It could be starvation due to either pump or blocked filter.

 

[Ian B Walker]

Is the fuel pressure under full load maintained Ok.? It could be starvation due to either pump or blocked filter.

Fuel pressure constant under load.

 

[Dieselman]

Back to crank sensor then I think.

 

[television]

The crankshaft sensor cant do that, its either good or bad and nothing in the middle so forget that.

If motronic check the switch inside the throttle housing, if it cant close , the revs could be anywhere.

A meter onto the contacts where it plugs in would give the answer

 

[Dieselman]

I'd disagree about the sensor, they can go faulty partially either due to magnetic whiskers on the tip or partial break in the sensor. It then throws the timing out.

It's had a new throttle body so unlikely to be the idle switch.

 

[Number_Cruncher]

Is load sensed on this engine by a manifold pressure sensor rather than a MAF?

If so, making sure the vacuum connection to the sensor is clear, and not full of oil or gunk is a quick easy check.

Is this car fitted with a lambda sensor & cat?

If so, does the lambda sensor switch properly? What are the lambda readings during the surge?

 

[television]

I'd disagree about the sensor, they can go faulty partially either due to magnetic whiskers on the tip or partial break in the sensor. It then throws the timing out.

It's had a new throttle body so unlikely to be the idle switch.

Sorry do not agree, it cant go partially in any shape or form.

It is an inductor, any short circuit, it could not work, open circuit it cant work either

 

[grober]

Has it got an electronic throttle/cruise control as opposed to a throttle cable? Might be a problem with the accelerator electronic sender module.
Other possibility is the dreaded wiring loom?

 

[GazCaff]

A few years ago, I had a VW Vento with exactly the same problem you are describing Ian. It was a faulty idle speed control valve, or throttle kicker as its otherwise known. I don't know if this is integrated into the drive by wire throttle on a petrol Merc but it might be worth checking.

 

[Ian B Walker]

Well today changed everything bar the ECU and Crank Position sensor. Spoke with a colleague in Formby and he spoke with his mate in Bosch. Try the coil packs said he. Nope been there done that got the tee shirt. Anyone got a spare box of matches and a ltr of petrol

 

[GrahamC230K]

Check the crank sensor and fuel distributor setup.

This was the first reply!

Hopefully that than the ECU.

 

[television]

This was the first reply!

Hopefully that than the ECU.

And for what its worth I said that was impossible to be that for that fault

 

[Ian B Walker]

This was the first reply!

Hopefully that than the ECU.

And for what its worth I said that was impossible to be that for that fault

15 - 40 new balls please

 

[television]

You need an oscilloscope on the outputs and inputs of the ECU to look at the wave forms and see the signal that is varying