Engine Problems/ Sudden Rev Drop / Then Increase

[Peter Burt]

Hi All

 

C5 2.0HDI 2006 82,000 Auto Estate

 

Right this has happened twice in 3 weeks we have owned the car, and garage does not know what is happening. so thought i would ask before giving them what for.

 

Driving along at 1500-2000 revs then all of a sudden the revs drop to tick over then back to normal then drop then back etc.... accompanied by an electrical smell/ burning sort of smell ( Mrs's description).

After the first time, had the codes read and the garage replaced the air flow sensor (i assume the Mass airflow sensor), car drove fine after this, now its happened again, garage has read and cleared the codes as there were too many to decipher which one was the problem.

 

Oh no warning lights have come on at all

 

Now in my opinion if it is the MAF that should put the car into limp mode and not affect the revs in the way described, its not the injectors as they would cause rough running at all revs, i would also expect it if the fuel pump was at fault.

 

Having looked for other threads the only one that looks similar is possibly the throttle pedal fault/ throttle assembly, but reading that the revs just drop not return to normal without restarting. Oh forgot to mention on the first episode the car returned to normal after a few miles and the second after a pause in use and a restart after about and hour.

 

Neither time has the fault been from start up, only after a few miles.

 

Any ideas gratefully received, luckily i brought the car with warranty!   

 

 

 

[paul.h]

If it happens again, make a note of the codes before deleting them and put them on here/do an internet search to see what they may mean. The burning smell - possibly a leaking injector seal - remove the engine cover and have a look at them. The fuel filter may be due for renewal, the diesel may be a bad batch. There may be a problem with the auto gearbox/control - there are some members with experience who may have some ideas and to check the gearbox a Lexia diagnostic tool would be needed.

 

Check that the warning lights work when starting up in case a bulb has gone.

[coastline taxis]

can you produce the fault or is it just at random. As you realy need to get into the live data on a scanner and see what the engine is doing when the fault happens. And dont be quick to rule the ingectors out as one of them might be sticking once in a while. try doing a leak of test. also is the smell plastic/oil/gas or diesel