Throttle position sensor problem?

[BenzComander]

Car is generaly running OK, but every so often it feels a little bit down on power, and on a very light throttle while cruising the engine judders and seems to surge, but with no increase in actual car speed.

While its doing these symptoms, if you accelerate or back off the throttle they disapear and the car seems to run OK for a while. But once it does it it is there for the whole journey!

The strange thing is though, that on some journeys it does not do it at all??

Have changed plugs, leads and MAS so far in an effort to diagnose the problem by myself (and as cheaply as possible ) so was wondering if it could be the throttle posistion sensor, and if so how much and how hard is that to change?

Thanks!

 

[grober]

If its a fully electronic throttle there will be 2 potentiometers one attached to the accelerator pedal and one as part of the throttle actuator assembly. If either has gone faulty or the tracks are dirty then you might get symptoms like you describe. However since the throttle actuator has many inputs in addition to the accelerator position input it might be difficult to check it. These units are pretty expensive so perhaps this is one time a visit to specialist/MB dealer with the correct electronic diagnostic equipment might be prudent? I think its also possible to clean up the throttle plate in these ETAs which might be worth a try. The only obscure fault I can think of is that it might be indicative of a AIR CONDITIONING PROBLEM cos the ETA gets a load signal from the air con among others. might explain the intermittent nature of the fault on some journeys only??