BMW Repair: Bmw E46, 320i 1999, intake leaks, bmw e46

Question
Hi Evan,

I have a 320i (1999) (VIN number can be provided later), and I live in Denmark. I have owned the car for 3 years (my dad owned it from new), and it has done about 90,000 miles.

For some time it has been acting a bit unpleasant when driving in low gears at lower RPMs. If for example I am approaching a traffic light in 2nd gear at around 2,000 rpms, and I get the green and accelerate (I do not floor it, but just average acceleration) the car has seems to be very jumpy. The RPM gauge shows engine not accelerating smoothly, and you feel you are getting a whiplash until the RPMs have surpassed around 3-3,500 - then it runs smoother again. The same thing happens in low rpms in all gears <3,000, but it is the most noticeable in 2-3rd gears. If i am very very gentle on the gas I can avoid the bumpyness, but that is not really the way to drive the bimmer ;-) Furthermore, if I ignore the whiplash and push the accelerator as I would normally do, the car has a tendency to be somewhat jittering when running idle at the next stop light etc. This jittering stays there in every idle situation for quite a while hereafter untill I park the car and turn off the engine. After the egine is off, I can immediately turn it back on, and the car is then fine doing idle.

I have tried to my local BMW service place (used to be official dealer, but due to restructuring of the dealer network in DK, is no more), and they have a hard time to find the solution. They have changed the plugs which helped for 2 weeks, but now we are back to square one. Also, they claimed that connecting it to the computer gave no imformation about error codes related to this. I do not know if this i related to the fuel pump, ignition coils or something completely different.

I very much hope you can help, as I am rather stuck at the moment whitout any solutions.

Answer
Lars, check rubber intake boots for cracks and leaking. I would try using a smoke generating machine to check for intake leaks. I would also check the idle valve for freedom of movement and sticking. Clean it out with solvent or replace it. Do the same with the throttle body. Replace any questionable seals. This sounds like a throttle or vacuum leak issue to me.
-Evan