Engine hesitation - BMW Forum

325i_family · 10-25-2005, 09:58 PM

I just replaced my o2 sensor because the check engine light was on and the engine was hesitating during acceleration. However there is still terrible hesitation usually in the low rpm's during acceleration and the check engine light still ocasionally comes on for the o2 sensor (I used the motronic code reader). Does anyone know what could be causing the hesisation. Within the last 3 months I put new spark plugs and a new fuel filter in. The hesistation is so bad I will not drive it untill it's fixed. My car is a 92 325i. Thank you everyone

97alpineM3 · 10-25-2005, 10:05 PM

Automatic I presume?

If so... when was the last time your tranny fluid was changed?

Have you checked your idle control valve... That might be a tad dirty... very common cause for hesitation.

If you have questions pertaining the procedures for cleaning the idle control valve or changing your tranny fluid... visit the FAQ/DIY forums...

Good Luck,

Les

thekid · 10-26-2005, 01:20 AM

Do you have idle problems as well as hesitation? that would support ICV being dirty or a vaccum leak. If not I would start with the fluids if it is an automatic.

Delmarco · 10-26-2005, 02:05 AM

what the heck is "transmission fluid"!???

People always generalize that...when all these things are transmission related fluids:
is it oil, diffs, power steering, brake fluids....?

am I missing something here?

///M Power · 10-26-2005, 02:09 AM

Transmission fluid is transmission fluid lmao

thekid · 10-26-2005, 02:42 AM

Quote:

Originally Posted by Delmarco

what the heck is "transmission fluid"!???

People always generalize that...when all these things are transmission related fluids:
is it oil, diffs, power steering, brake fluids....?

am I missing something here?

yes, there really is fluid in the tranny. So tranny fluid would be that fluid in there. There is even a dipstick to check it on most cars, just check it while it is warm.

DesmoBob · 10-26-2005, 03:43 AM

just a couple of q's to narrow down the possibilities:
- does it hesitate regardless of engine temp? or only when cold? or only when warm? or it doesn't matter?
- is it under hard acceleration (heavy load) or moderate acceleration (partial load)? or both?
- any hesitation/stuttering/gasping at idle?

from your description, it sounds like a fuel delivery problem, but there may be more to it if you can provide more info. your engine light may be a completely separate issue.
things you may consider:
1) fuel pressure regulator - regulates low or high pressure
2) injectors - dirty or leaks
3) fuel pump - must provide pressure at least a pressure higher than the regulator regulates

if i interpret your description correctly, offhand it sounds like it could be regulator because it hesitates when you get on the gas. a faulty regulator can cause fuel starvation because of poor delivery or lagged delivery (output) or poor metering of intake vacuum (sensory, it meters off intake vacuum). if it is because of poor input pressure (input), that is actually a bad fuel pump.

DesmoBob · 10-26-2005, 03:47 AM

btw, before anybody points this out, devices can be faulty even if they don't throw a CEL.

325i_family · 10-26-2005, 10:02 AM

Thanks for the quick response. The car has a manual transmission. The car also is rough at idle now. I will try using some "seafoam" to clean the fuel injectors and if that doesn't work I will check the ICV. Thanks again.

thekid · 10-26-2005, 01:47 PM

The other thing to check is going to be the vacum hoses, if cleaning the fuel injectors (I recommend 44k for that) and the ICV. To check for vacum leaks, just spary carb cleaner slowly on the hoses. If the engine rpms increase, the the hose you just sprayed has a leak. You can isoloate the leak and try to patch if you want, or just replace the hose, its cheap either way.

94BMW325i · 10-26-2005, 09:52 PM

Quote:

Originally Posted by Delmarco

what the heck is "transmission fluid"!???

People always generalize that...when all these things are transmission related fluids:
is it oil, diffs, power steering, brake fluids....?

am I missing something here?

You need fluid in a transmission or it would always be metal on metal contact wouldn't it?
Meaning that you would always hear gears grinding and need a rebuilt trans every few months.

SpooldUp · 10-28-2005, 04:05 PM

Quote:

Originally Posted by 94BMW325i

You need fluid in a transmission or it would always be metal on metal contact wouldn't it?
Meaning that you would always hear gears grinding and need a rebuilt trans every few months.

Months? It would be a matter of minutes.
Maybe Del was talking about ATF verses gear oil vs 'BMW synthetic tranny fluid' etc.??

triggrhaapi · 10-28-2005, 04:22 PM

Quote:

Originally Posted by Delmarco

what the heck is "transmission fluid"!???

People always generalize that...when all these things are transmission related fluids:
is it oil, diffs, power steering, brake fluids....?

am I missing something here?

only two of those are transmission related fluids. Gearbox oil is also called transmission fluid. In fact some BMW Manual transmissions use automatic transmission fluid as lubricant. Diff oil is called diff oil. Gearbox fluid is called transmission fluid.

As I'm sure you're aware, brakes and power steering are not transmission parts.