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Old 10-28-2019, 06:50 PM   #1
ERK IV
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Bucking under full throttle in 1st gear

My 2002 330ci recently started having issues after sitting for a week while waiting for a new radiator. Car is at 195k miles and stick shift. Has had a clutch replacement 20k miles ago, alternator, fuel pump and filter/regulator. Cleaned the MAF and IAC. Rebuilt the DISA valve, and replaced the cam positioning sensor.

Any time I try to get over 3/4 throttle in first gear, sometimes second, the car will buck very badly, almost like traction control kicking in, but the traction control light does not come on, and this issue persists with traction control completely off. It does have a flex fuel kit from Advanced fuel dynamics, but the problem persists on full ethanol and full 93.

The car is flashed over to EU2 tune thanks to a helpful member of this form, and I tried scanning for codes with INPA but kept getting error #28 in the api.

Any suggestions?
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Old 10-29-2019, 03:35 AM   #2
Dogthebountyhunter
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I'm betting it's time to change the cats.
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Last edited by Dogthebountyhunter; 10-29-2019 at 03:37 AM.
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Old 10-29-2019, 07:14 AM   #3
dmax
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If it's not an airleak, perhaps at the lower intake boot, then I'm going to guess it has something to do with whatever work you did just before your issue arose. Did you use MAF cleaner for your MAF? Other cleaners will mess it up (so I've read). Did you check your disa valve operation? (Plug the hole to see if the flap stays open?)

Good luck...and a bump.
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Old 11-10-2019, 10:47 PM   #4
ERK IV
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Quote:
Originally Posted by dmax View Post
If it's not an airleak, perhaps at the lower intake boot, then I'm going to guess it has something to do with whatever work you did just before your issue arose. Did you use MAF cleaner for your MAF? Other cleaners will mess it up (so I've read). Did you check your disa valve operation? (Plug the hole to see if the flap stays open?)

Good luck...and a bump.
Those repairs all happened atleast 6 months ago. Didnt have any problems until this issue arose after replacing a leaking radiator.
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Old 11-11-2019, 03:00 AM   #5
bendoscopy
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+1 on cats. Had the same issue with my 320Ci. Clutch was good, no air leaks, fuel system replaced. Narrowed it down to cats.

Your description of bucking is exactly what I had.

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Old 11-11-2019, 03:07 PM   #6
NZ00Z3
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Also check your DISA to make sure its working properly. A faulty DISA will cause bucking under hard acceleration at around 3,500 rpm
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Old 11-11-2019, 09:33 PM   #7
Jackson42
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Does it manifest itself as a pulsation with a definite period of a quarter to half a second or so?
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Old 11-11-2019, 10:06 PM   #8
Archbid
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Any codes?
Also MAF cleaner is worthless on this engine. There are no upstream sources of contamination. You are well beyond the replace by date for your MAF, btw.
Age of pre-cat O2 sensors?
Fuel trims?
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Old 11-11-2019, 10:07 PM   #9
Archbid
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You can get the cats tested, or use a scope to see if blockage is obvious.
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Old 11-11-2019, 10:27 PM   #10
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Any codes?
Also MAF cleaner is worthless on this engine. There are no upstream sources of contamination. You are well beyond the replace by date for your MAF, btw.
Age of pre-cat O2 sensors?
Fuel trims?
Agreed, MAF cleaners wont do any good, and it tends to fail soft, no codes, no obvious difference by graph reading, unless you replace it with new one you wont see difference.

Yes your symptoms sound like a cats.
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Old 11-12-2019, 02:09 AM   #11
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Watch this
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Old 11-12-2019, 02:37 AM   #12
Anticdubai
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Clogged cats can still do their job to burn exhaust fumes, but resist to the flow to decrease performance to the point car become undrivable. You cannot diagnose it any way but either connecting manometer to pre-cut O sensor hole or using endoscope.
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