Engine revs up like mad
 

Hi all, this is my 1st post on here, just had a question thats been bothering me for a few weeks now, my car is a 58reg Mercedes W204, c200 cdi, the thing is everytime i start this car up the rev goes up and down like mad then after around 20 seconds its back to normal. i have always used shell or bp for my fuel.

could anyone tell me please what could possibly be the problem here.

your help is much appriciated.

Sounds like an O2 sensor fault, which should show up on a MB Star system scan. The ECU advances the idle for a 20 second warmup but if the exhaust sensor is defective, can cause the ECU to think no fuel is arriving at the engine and open the injector system to feed more diesel.

thanks for the reply, my car was in with the dealers a week ago, at that time i had the problem but not as bad as it is now, is there any chance it has trigered the sensor off now, because when i spoke with the dealers all they said was they couldn't find anything wrong with the car.

could this be the reason for poor mpg? as i only get between 25-28mpg and its a c200?

and also is this a big job/expensive job?

regards

Most likely the sensor, could definitely be a reason for your "poor" mpg versus the norm. If you could take a video of the issue and post it to YouTube it would better help us diagnose the issue. It could also be shown to your dealer if the issue doesn't persist when you bring it in for service.

got my car booked in, in the morning lets see what i get back from the dealers

had some problem booking my car in last week, but its gone in now, fingers crossed hope its nothing major, what do you guys think this might be related to?

Well, it could have been a defective injector that stayed open until the engine reached a certain temperature? I am not sure this would show up as an error code.

still not heard anything from dealers so no new is good new hopefully :-)

hi guys just thought give you guys an update got my car back and they found a fault with the car and said it is the 3rd injector that is causing the problem, and have quoted my close to 600quid for the repair, any thoughts on this guys?

A while back I used to fix the injectors on a Porsche 4 cyl pancake engine, pulling the injector, applying a 12 volt charge to open the needle, and trying to clean out by backwashing the injector point to get out whatever was causing the needle to stick.

Of course, if this is an electromechanical fail (not a block) of the injector, it needs to be replaced. This is a very simple job, you can DIY or take it to any reputable service garage. There is no calibration, plug and play.

so why the hell are the bugers chargin me so much for this job, yes might just see if i can take it to my local garage, if i carry on driving like this for a few weeks will it cause any further problems?

You should get it fixed RIGHT AWAY, when an injector is open, you risk running the engine to the red line until the electronic limiter cut the ignition.