For about the past 4 or 5 months, i am having uneven acceleration when driving at a constant speed. It is very random how often it occurs.

So say i am driving 45 mph, the engine feels like it will "hiccup" every few seconds. It is so noticeable that a passenger will pick up on it.

I have an 04 545 with 60k. Maint is up to date, and i even just changed my plugs to try and see if that would help. I thought that worked, but had the problem again this morning on the way to work.

I have taken it to the dealer. They couldnt replicate it in their 5 minute test drive. It is just too random.

Any thoughts???

 

have you tried the 25 second transmission reset?


Turn the key in the #2 position or push start so engine lights show up but the car doesn't start (only electronics on). Press the gas pedal down all the way into the kickdown position. HOLD your foot there for 25-30 seconds. The trans / throttle should reset to stock, you may or may not hear a slight "ting" or "knock"

 

I will give the reset a try and post results. thanks for the info.

Any other input/ideas would be appreciated as well!

 

Same problem after tranny reset =/

 

what kind of plugs did you use?

I had a similar problem on a past 540i. I had put some cheap champion plugs in and it did the same thing. The solution was to put the BMW recommended Bosch Platinum +2's in and it fixed my problem. Just a very picky motor I guess

edit: just noticed you said you changed them after the problem occured, hmm

 

Have you tried injector cleaner? I had similar symptoms - constant speed in city or slow speed areas (5th gear, 35 mph, etc) with the hesitation, misfire or whatever it was. Started using injecter cleaner routinely and I have reduced it to almost non-existant (no problems in last 3k miles). I am at 89k and no plug change yet and we have same drive train except for rear end ratio.

 

Yea, the problem was happening before the plug upgrade - that is why i did it.

I used the best available, the new Bosch Fusions. The car starts and idles better. But i still get the uneven aceleration, when driving at a constant speed. It is weird it just take a hit every 3 seconds or so. feels like the engine just loses power for a split second. I can see the tach bump down and back up when it happens. And it doesn't always happen, that is why the dealer did not feel it.

I had something similar years ago with a GMC pickup, that i had changed the distributor cap and coil on. That is why i assume the problem is somewhere in the ignition system.

Let me know if anyone has any suggestions please.

 

I will try the injector cleaner - what do you recommend? I have read here that some like techron.

 

Have the o2 sensor checked and the mass air flow sensor

 

Crazy....I just noticed my car did the same thing a few days ago when i was off driving around....Let me know if you find anything out...I was going to mention it the next time I went the the dealer!