[Merlin82]

Well I thought i would post on here to see if anyone may be able to help me diagnose a slight stumble Im experiencing in my 2011 X3 35i. When you accelerate in a "spirited" manner, even if not being extremely agressive, you can feel the car kinda stumble or hiccup a couple times. It used to be very smooth accelerating, but now you can feel it do this whenever you want to accelerate a little harder. The plugs had been changed last year, but just to rule them out I put in new Bosch plugs gapped to .022, and new Delphi coils to go with them. Tried taking a look just a little while ago to see if I could see anything disconnected but no luck. Are there any vacuum lines I should be trying to check? Could this be something else? Was hoping someone here may be able to help me trouble shoot.

[Merlin82]

Ill mention that I also have an MHD Stage 1 tune installed on the vehicle with the Remus exhaust being the only real mod. I thought maybe it was the tune so flashed it back to stock but still notice it doing it. Not sure if it could even be a symptom of a charge pipe with a small leak or something.

[najnad]

I had a similar problem, turned out to be a bad spark plug

[Merlin82]

That was my first thought when it started a month or 2 ago, but the NGKs were only in for maybe 10 months when it started, and i changed them and the coils first to try and eliminate those as a problem.

[najnad]

if you are positive the plugs and coils are good and installed correctly, how about the fuel filter and the fuel injectors?

Have you tried any data logging on torque app or similar to see if the sensors pick up anything?

[Merlin82]

So ironically I had a weird feeling and tried swapping out my tires to my winters and the stumble is gone. Went out a bunch tonight and seems like swapping wheels/tires fixed it. The summers are a set of 20" 310M wheels with 245/40/20 in the front and 275/35/20 in the back. Tires are Goodyear Eagle F1 asymmetric. So not sure if mine just doesn't like staggered sizes or of the tires I got weren't any good since I did get them slightly used. Gonna try swapping back to make sure but looks like that may be the cause of everything.

[Merlin82]

Swapped back on the summers and once they were back on the stumble was back. So it looks like the problem is somewhere with the tires or transfer case. Not sure if there is any way to have the transfer case tested. If i have to buy new tires and its the goodyears causing the problem i have no problem doing that. I just dont want to buy new tires and find out that it is the transfer case causing the problem.

[tracer bullet]

FYI asymmetric tires can be run backwards. Not recommended long term but for a few short trips nothing bad will happen. You could try swapping L / R wheels, thereby changing the tread pattern, and give it another test?

[najnad]

Hmm...if the X3 thinks all 4 tires are the same, but then you put wider tires on the rear, does the computer interpret the extra grip in the rear as something is wrong and applies some electronic nanny to prevent you from losing control, even momentarily?

[Merlin82]

Originally Posted by najnad

Hmm...if the X3 thinks all 4 tires are the same, but then you put wider tires on the rear, does the computer interpret the extra grip in the rear as something is wrong and applies some electronic nanny to prevent you from losing control, even momentarily?

See and thats what Im wondering. If there is maybe a problem in the transfer case or the adaptations for it. Or if i just have a crappy set of tires and need to buy new tires.