Emission control fault?

[lordluvitt]

Hello all,

I have had a performance issue with my '98 C180 manual petrol W202 for a while. Engine lacks power (can't overtake anybody) and suffers from mild fluttering of revs (more severe over 3000rpm). Just lately I have found that the car is completely undrivable (no power whatsoever) until the water temp gauge reaches around 45deg. After this the car pulls away okay but not 100% perfectly.

I have been thinking that this is either a fuel starvation fault, air/fuel mixture issue, or timing fault. But because there is a marked difference in the symptoms between different temperature readings, I was looking for an element in the system that was temperature governed.

All of the faults listed in the Haynes manual suggest an air or vacuum leak at the throttle body but I have also discovered that the Evaporative loss emission control system contains a thermo-valve which is governed by the water temp and is linked to the throttle and ensures correct running at cold temperatures. Sounds like a possible cause of fault?

If this sounds right I need to know whether I have such a unit fitted to the car. The Haynes manual lists two evaporation emission control systems, an HFM-SFI and a PEC system. Only the PEC system has the thermo-valve. How do I know which system is on my car? And if I have a thermo-valve, where would it be located?

Thanks.

 

[GCLTuning]

Hi have you looked at the MAF sensor or EGR valve ?

If it is the MAF you just simply disconnect it the should be an improvement (then you will need to replace it)

If its the EGR valve take the vacuum hose off and there should be an improvement (then you will need to replace it)

By doing this you will set the parameters to the default setting allowing you to diagnose the fault .

 

[lordluvitt]

Thanks for the reply.

The MAF sensor was suggested sometime ago and this was thoroughly cleaned with electrical contact cleaner with no improvement noted to the engine running. In fact it appeared to be spotless when I first looked at it. I will unplug it and see whether anything changes.

I am not sure what the EGR valve is. Could you tell me where this is located and which hose to take off please (where the hose comes from or goes to).

As the engine runs very differently between being cold and when warmed up, should I try these two tests when the engine is cold or warm?

 

[GCLTuning]

Hello all,

I have had a performance issue with my '98 C180 manual petrol W202 for a while. Engine lacks power (can't overtake anybody) and suffers from mild fluttering of revs (more severe over 3000rpm). Just lately I have found that the car is completely undrivable (no power whatsoever) until the water temp gauge reaches around 45deg. After this the car pulls away okay but not 100% perfectly.

I have been thinking that this is either a fuel starvation fault, air/fuel mixture issue, or timing fault. But because there is a marked difference in the symptoms between different temperature readings, I was looking for an element in the system that was temperature governed.

All of the faults listed in the Haynes manual suggest an air or vacuum leak at the throttle body but I have also discovered that the Evaporative loss emission control system contains a thermo-valve which is governed by the water temp and is linked to the throttle and ensures correct running at cold temperatures. Sounds like a possible cause of fault?

If this sounds right I need to know whether I have such a unit fitted to the car. The Haynes manual lists two evaporation emission control systems, an HFM-SFI and a PEC system. Only the PEC system has the thermo-valve. How do I know which system is on my car? And if I have a thermo-valve, where would it be located?

Thanks.

My fault sorry your's is a petrol there for it will not have and EGR valve .

 

[GCLTuning]

The MAF being unplugged will have an instant effect. This will make the car run better or worse go for a short drive and see if there are any changes .

 

[lordluvitt]

I've just returned from an indie MB garage in Leicester. They suspected a faulty MAF as well and swapped mine with a fully working unit. The difference in the running of the engine was apparent, although this was only demonstrated at standstill and not on the road.

So well done GCL, looks like you were right. Now I need to get hold of a replacement unit. The garage wanted £240 for the new part and fitting so I said no. I have read that someone on here got one for £60ish.