[danielm11]

Hi all! Came on to the forums to see if I could get any help with the issue that I am having with my 2006 BMW 325i Xdrive 6 speed manual with 197k miles. While driving the car it’ll buck/jerk mildly aggressive and drive normally right after. This situation happens very randomly and has happened in all gears 1-6. It feels like the car cuts off and cuts back in. The RPMs will drop and go back to normal as well. No CEL comes on either. I’ve replaced all 6 coils with BOSCH and along with spark plugs as well. I am not sure if this is related but I also replaced the battery, alternator, belt, belt tensioner, pulleys, oil filter housing gasket. The car idles perfectly fine and doesn’t jump around and also drives smoothly other than the random bucking. I suspect it’s a fuel related issue but without the car throwing any codes I am not 100% sure and that’s why I came on here to see if I could get anyone’s opinion/help on my issue. If anyone could help me out that would be amazing thanks!

[drawz]

Did you scan for codes with a tool that can read BMW specific codes? Being an xdrive, you have to consider a transfer case issue. If you haven't already, change the transfer case fluid and inspect both the front and rear driveshafts.

[danielm11]

I havent scanned for any codes nor changed/checked the condition of the fluid in the transfer case since my ownership which I’ve owned the car for about a year and a half and bought it with 173k miles. I think I’ll check the codes first and see if anything pops up. Do you have any recommendations for a bmw specific code reader?

[lowrydr310]

Sounds like a fueling issue but hard to say for sure. If so there will most certainly be a stored code.

The simple but not cheapest solution is BMW Protool. I won't post links but there are tons of resources. A cheaper option is a K+DCAN cable and BMW Standard tools suite.

[oVeRdOsE.]

do the obvious and easy step 1st .

1- scan
2- clean the vanos solenoid
3- battery health

then start digging.

idle issues are often related to the vanos solenoid, and they are very accessible from the front, 1 bolt each

[danielm11]

Originally Posted by lowrydr310

Sounds like a fueling issue but hard to say for sure. If so there will most certainly be a stored code.

The simple but not cheapest solution is BMW Protool. I won't post links but there are tons of resources. A cheaper option is a K+DCAN cable and BMW Standard tools suite.

Originally Posted by oVeRdOsE.

do the obvious and easy step 1st .

1- scan
2- clean the vanos solenoid
3- battery health

then start digging.

idle issues are often related to the vanos solenoid, and they are very accessible from the front, 1 bolt each

Thank you for your guy’s response. I’ll start off by reading the codes first to see if anything is stored. I have to order the K+DCAN cable online since I don’t have one. I’ll report back with some more info as soon as I get the car scanned.

[Andrewiffic]

I had very similar issues with my car shortly after I bought it and I was going crazy trying to figure it out. Turns out the previous owner had changed one tire and it happened to be slightly different overall diameter than the other 3. Once I put on a set of matching wheels+tires it completely went away.

Just an idea that may get overlooked. Good luck!

[Brian86]

Are your front tires a smaller diameter than your rear tires?

[danielm11]

Originally Posted by Andrewiffic

I had very similar issues with my car shortly after I bought it and I was going crazy trying to figure it out. Turns out the previous owner had changed one tire and it happened to be slightly different overall diameter than the other 3. Once I put on a set of matching wheels+tires it completely went away.

Just an idea that may get overlooked. Good luck!

Thanks for the heads up! When I got my car I ended up getting new wheels and tires for the car. They are the same diameter but different widths I have 19x9 in the front and 19x9.5 in the rear.

[danielm11]

Originally Posted by Brian86

Are your front tires a smaller diameter than your rear tires?

They are not both front and rear wheels and tires are 19 inch but they are different widths. I have 19x9 in the front and 19x9.5 in the rear

[Brian86]

https://tiresize.com/calculator/

Wheel diameter is not the same as tire diameter. Go do the math.

You probably have shorter tires in the front. This causes problems with the transfer case.

[danielm11]

Originally Posted by Brian86

https://tiresize.com/calculator/

Wheel diameter is not the same as tire diameter. Go do the math.

You probably have shorter tires in the front. This causes problems with the transfer case.

Tire diameter difference between the fronts and the rears are .1”. The front is 26.1” and the rear is 26”.

[oVeRdOsE.]

might be the front drive shaft too.

Get under the car and try to turn it / wiggle it by hand. Youll see if the u-joint are loose.

Symptoms of a bad front drive shaft are not exactly what you've described, but it can make the driving weird. Mine was like kicking depending of the throttle.

[cyow5]

Are you sure the rpm drop? Being a manual, the rpm can't drop unless you clutch in, something in the driveline disengages, or the tach goes dead.

I had very similar symptoms that I traced to an improperly installed crank sensor. It would inconsistently blink out (like one out of three drives) and felt like the car was slamming the brakes. Rpm would drop but not because the engine actually slowed down but because the ECU sent the dash a low rpm. A dying ECU or all sorts of other sensor/electrical problems can do this, so whether or not the rpm *actually* fell is a huge clue.

[danielm11]

Originally Posted by cyow5

Are you sure the rpm drop? Being a manual, the rpm can't drop unless you clutch in, something in the driveline disengages, or the tach goes dead.

I had very similar symptoms that I traced to an improperly installed crank sensor. It would inconsistently blink out (like one out of three drives) and felt like the car was slamming the brakes. Rpm would drop but not because the engine actually slowed down but because the ECU sent the dash a low rpm. A dying ECU or all sorts of other sensor/electrical problems can do this, so whether or not the rpm *actually* fell is a huge clue.

The rpm’s on the dash would drop around 100-400 rpm while the jerk/buck happens and then it would kick back up to the normal rpm. For example, if i’m going 70 and my rpm’s are 2500 and then the jerk happens the rpm would drop to like 2200 and then kick back up to 2500 and drives totally normal again. This issue is very random and doesn’t happen everyday. Sometimes it’ll happen once but I’ve had it buck like 3-4 times in a row and would throw a CEL for a second and then CEL would go away and not come back.

[oVeRdOsE.]

^ really looks like solenoid, I had the exact same behavior, but worst, if I let the car idle for 3-4 seconds, it would shutoff.

worth trying anyway, it's a few minutes job, and it required brake/carb cleaner and a 12v source to activate the solenoid. 9v battery is not strong enough.
Ive simply used crocodile wire to the car battery.

it can be overstuff, like tb, valvetronic, sensors, vacuum leak. But vanos is the easiest one to check.

[danielm11]

Originally Posted by oVeRdOsE.

^ really looks like solenoid, I had the exact same behavior, but worst, if I let the car idle for 3-4 seconds, it would shutoff.

worth trying anyway, it's a few minutes job, and it required brake/carb cleaner and a 12v source to activate the solenoid. 9v battery is not strong enough.
Ive simply used crocodile wire to the car battery.

it can be overstuff, like tb, valvetronic, sensors, vacuum leak. But vanos is the easiest one to check.

https://www.youtube.com/watch?v=FWJYvKcOAFk

i’ll definitely have to check it out seems like solenoids are a common issue on these things

[cyow5]

Originally Posted by danielm11

The rpm’s on the dash would drop around 100-400 rpm while the jerk/buck happens and then it would kick back up to the normal rpm. For example, if i’m going 70 and my rpm’s are 2500 and then the jerk happens the rpm would drop to like 2200 and then kick back up to 2500 and drives totally normal again. This issue is very random and doesn’t happen everyday. Sometimes it’ll happen once but I’ve had it buck like 3-4 times in a row and would throw a CEL for a second and then CEL would go away and not come back.

If you are still in gear, it'd have to slow to 60mph and then back up to 70 for those rpm. If that doesn't sound like what it did, then I'd look squarely at the crank sensor. That was the root of my issues, and they fit *exactly* what you are describing. It could also be the ECU or any wiring in between the ECU and crank sensor. I don't know the ECU logic well enough to say if it'll drop the rpm reading if there's a VANOS error, but I don't see why it would. It would certainly drop the rpm reading though if you missed a tooth or two on the crank signal.

[cyow5]

Originally Posted by oVeRdOsE.

^ really looks like solenoid, I had the exact same behavior, but worst, if I let the car idle for 3-4 seconds, it would shutoff.

worth trying anyway, it's a few minutes job, and it required brake/carb cleaner and a 12v source to activate the solenoid. 9v battery is not strong enough.
Ive simply used crocodile wire to the car battery.

it can be overstuff, like tb, valvetronic, sensors, vacuum leak. But vanos is the easiest one to check.

What's tripping me up is the 400 rpm. Is that also consistent with your experience? Auto or manual? If auto, I'd believe it because it can drop out of gear and then back. Manual, not so. If the tach falls on a manual faster than physically possible, it is because of the *measured* rpm and not the actual rpm

[SlowE92]

Sounds a lot like a vanos/fueling issue. When my car started doing this it was actually my fuel breather valve had cracked.