Q&A

Sounds like you are starting to get an exhaust leak, possibly at the exhaust manifold. This would account for the noise, and it could also be interfering with the O2 sensor readings, causing the hesitation.

I like munkyrench's answer, but you don't mention if the check engine light is on or not. An exhaust leak knocking the O2 sensor far enough off to cause a hesitation should be setting some codes.

i just had my '06 330i 50k miles in the shop for the same reason. bmw has a "tsb" (technical service bulliten) out for this problem. i had to have the exhaust lifters & push rods replaced in the engine. they are known for this model to have this problem frmo the factory. guess a "tsb" is bmw's term for recall.

Go to Walmart and buy Chevron Techron Fuel injector cleaner. Pour it in when your almost ready to fill up with gas, and then fill your gas tank with premium fuel. Your car will run like new again. Just tried this stuff today on my car. Paid $12 for it and my car has some punch to it now. Really makes a difference for less $$

With that series there's an issue with the VANOS system whose symptoms sound quite a bit like that. The car will run louder rougher, will get poorer gas mileage, and will hesitate below 2-3k RPM but especially off the line. The seals used in the system are made of a material that will only hold up to temperatures of 100F and that is known to deteriorate under prolonged exposure to synthetic oils (which is exactly what should be running in your motor). BMW will only replace these seals with the same thing and you'll be looking at the same problems creeping up after a couple years. Go to: http://www.beisansystems.com/procedures/vanos_procedure.htm for a better breakdown of the issue and repair. This company offers a kit that includes seals made out of the material that should have been used in the first place. The kit is relatively cheap and FAR cheaper than it would cost you to have a shop tear into your valvetrain.

I had a loud ticking noise in my 2003 330i that became noticeable at about 50,000 miles. The BMW dealer's initial remedy for this problem was to replace all the belts, which made a difference for a while. But there was still a soft ticking noise that could be heard at idle that became more pronounced over time. Eventually, I took it back to the same dealer. This time, they concluded that the noise was coming from the oil pump, which they replaced. Was it really the oil pump making that noise? I can't be certain, but I do know that whatever repairs they made banished the noise completely, and it hasn't returned. An oil pump failure could be a serious and very costly problem, so I'd urge you to give this possibility careful consideration, too.

I experience the same hesitation problem with hard acceleration from a standstill in my 2003 330i, and answer #5 ("Best Answer") is therefore of great interest. I'll have a mechanic look into this, or I might even do it myself. Thank you for raising this issue!