Throttle tip-in issue/stumble (3.0 5-speed)

Masospaghetti · #1 03-02-2025, 06:07 PM

I have a throttle tip-in stumble that seems fairly common for the M54 engine but in doing research haven't found any smoking guns. Before I open up the parts cannon I wanted a bit of help troubleshooting. Just over 160k miles on the vehicle and pretty much all original except for the stuff I've done.

Just off idle, when trying to accelerate, the engine feels like it bogs down for a split second before it catches. Once it catches, the engine feels healthy.

I've been poking around OBDFusion and INPA for anything obvious. The sample rate is slow for either so its hard to see transients like this, but nothing obviously off with the mass air flow, air intake temp. I also did a smoke check on the intake to check for vacuum leaks and did not find any. Long term fuel trims on both banks is +1.6%. No stored codes.

I've already replaced the plugs and the VANOS seals as I read these can cause similar symptoms, no obvious difference from either. I have not yet replaced the coils, MAF, or O2 sensors.

One thing that seems odd in INPA - checking the PWG/MDK values (the pedal position sensor vs throttle position sensor), intuitively these should roughly be in sync with each other unless I am understanding this system incorrectly. I assume there are redundant sensors for both to measure the driver's desired throttle input and and actual throttle position. the PWG sensors react immediately but the MDK ones barely change. Also, the sensors for each set aren't in sync with each other (i.e the two PWG sensors have an offset, and the MDK sensors appear to be inverted, one reads 0.5 volt and the other reads 4.5 volt). I posted two images, one at no pedal input and the other with some nominal level of throttle input. Does this mean there's something up with my throttle body?

Any help here is appreciated. Oh, also this is one of those rare 5-speeds. Other than the tip in issue it's great fun to drive!

andrewwynn · #2 03-02-2025, 06:48 PM

I thought both the pedal position and the throttle position used inverted secondary pots. I haven't polled mine in a while and can't remember for sure.

If i get a chance i can look but newer chassis so there is a chance they changed since then.

Masospaghetti · #3 03-02-2025, 08:42 PM

Quote:

Originally Posted by andrewwynn

I thought both the pedal position and the throttle position used inverted secondary pots. I haven't polled mine in a while and can't remember for sure.

If i get a chance i can look but newer chassis so there is a chance they changed since then.

From trolling the E46 forum, that's what I thought too. What I'm seeing doesn't make a lot of sense.

Effduration · #4 03-02-2025, 07:07 PM

Have a search among the E46 crowd…If anybody has figured it out, it’s the e46 crowd…

No disrespect to this forum…

https://www.e46fanatics.com/threads/...ix-mod.946536/

Masospaghetti · #5 03-02-2025, 08:44 PM

Quote:

Originally Posted by Effduration

Have a search among the E46 crowd…If anybody has figured it out, it’s the e46 crowd…

No disrespect to this forum…

https://www.e46fanatics.com/threads/...ix-mod.946536/

Yeah I've been reading on the E46 forum and bimmerforums. So far I saw one guy who said a new MAF fixed it, and another who said he had excess carbon buildup from running hot.

Effduration · #6 03-02-2025, 09:50 PM

Quote:

Originally Posted by Masospaghetti

Yeah I've been reading on the E46 forum and bimmerforums. So far I saw one guy who said a new MAF fixed it, and another who said he had excess carbon buildup from running hot.

I haven't used either, but what about Sprint Booster OR mapping the throttle yourself with MS4x.net ?

They look more promising than the MAF or carbon buildup.

https://www.e46fanatics.com/threads/...oster.1315523/

Masospaghetti · #7 03-03-2025, 04:49 PM

Quote:

Originally Posted by Effduration

I haven't used either, but what about Sprint Booster OR mapping the throttle yourself with MS4x.net ?

They look more promising than the MAF or carbon buildup.

https://www.e46fanatics.com/threads/...oster.1315523/

I've done this sort of thing on a motor- and ecu-swapped Fiero in another life, but on a stock X5? If I knew the car came this way then I'd be open to trying it.

Effduration · #8 03-03-2025, 04:59 PM

Quote:

Originally Posted by Masospaghetti

I've done this sort of thing on a motor- and ecu-swapped Fiero in another life, but on a stock X5? If I knew the car came this way then I'd be open to trying it.

I think it does come this way... You've described the standard M54 drive by wire lag.. It's why a lot of people prefer the drive by cable of M52 and earlier