E46 constantly reving

Stky10

I noticed a problem in my 3 series (E46) on friday. I was stuck in traffic on a flat surface, so was out of gear. I noticed that the engine started constantly reving and then dropping between 1500 to 2000 revs. I turned the car off for 30 seconds, then restarted it and all was fine. The same thing happened later that night though (again fixed by turning off and then on again), but hasn't happened since.

Anyone have an idea of what might be going on and how much it should cost to fix?. For it to happen twice in one day makes me think that there's some part on the way out, so its going to gradually get worse in the next couple of days/weeks, but if I can get it changed before it goes completely it might prevent it breaking something else as well.

cianclarke

Best bet might be to get somebody to hook you up to a code reader, if there's anything wrong it's very likely that will show it up - you might even be able to find somebody to do it for free.

HashSlinging

Hazzard a guess that its the MAF sensor.

There are a number of thing that can cause this. A small air leak can cause a rough idle or I had an issue with a camshaft sensor which was giving a rough idle in my e46. If the engine light is on a code reader should give some answers but you will have to go to a garage which has the equipment to do BMW diagnostics.

unkel

Or a dirty throttle body?

listermint

Hi

I had the same problem after a recent service (4 Weeks ago). Pain the in the royal one.
Anyway firstly after service, car was misfiring. Checked all the leads and the rest. Read the codes and displayed misfire on 1 and 2. So though that the coils had gone, but since plugs were new had some doubts. Threw in old plugs. Worked fine. So guy had given me wrong plugs ( shoulda checked but didnt)

Anyway. After misfire solved . Next day car starts revving by itself when stationary at lights. . Took it home and opened her up again checked it over. Turns out that I had not fully put the Hose from the Air filter box to the intake on fully. re-jigged and settled. Everything ran fine.

next day different lights, car starts revving again. Banging my head of wheel at this stage. Took home again an went over with fine tooth come.
Finally turns out some of the oil from the service had gotten into the crank shaft sensor (left one facing the engine ) With this cleaned and everthing tightened back up. All works great. 2 and half weeks running like a dream.

I would say first port of call is the Air intake. Make sure that hot air from the engine is not getting into the system This can give the sensors faulty reading. >> Car overrevs to prevent stalling as it thinks it has not got enough air coming in.:cool:

Oh an scratch your head alot. That helps

Secondly throttle body MAY need clean (may)

Stky10

Leonardo Flat Shuffleboard wrote: »

If the engine light is on a code reader should give some answers but you will have to go to a garage which has the equipment to do BMW diagnostics.

No dashboard lights on so far

Its been recently serviced about a month ago. I'll talk to the mechanic and see what he thinks.