[AndyW]

UPDATE: If you follow the whole thread you will see the problem was solved by reset of ECU to defaults. Leaving rest of original post for posterity.

Note: Starting a new thread to separate this issue from my previous CP gasket leak thread that unmasked the problem. Has been going on for ~8K miles. Car is well maintained by a CDO person -me. (CDO is like OCD but the letters are in the correct order., like they should be..)

Video of behavior here:

https://www.youtube.com/watch?v=wWnYEbxtnu4

This is a sequence with constant 3% accel position(but cycling throttle and RPM - see datazap of a similar run below), then idle(smooth), then rev to 2K(smooth).

Datazap of behavior here: http://www.datazap.me/u/andyw/thrott...10-11-12-13-20 <- NOTE: This log is not synced with video - took log after video since same phone used for both.

Summary of problem: Between ~2-4% accelerator pedal position, throttle position varies about 1-6%. Car idles fine. Above about 2K, fine. Behavior exhibits on the road as well. No codes. Frustrating problem. Have seen others post of similar issues on this forum and others so have done a LOT of research and have tried to eliminate things logically (to the tune of about $1500 or so in parts, at this point. Car has 120K so $$ not really a "loss", per se - new parts is still a refresh IMO) This problem manifests on the road in slow commuter traffic and in driving slowly around a parking lot so makes the throttle response frustratingly unpredictable and jerky sometimes.

Infuriating that the last two tiny crap cars I rented on my business trips had better response at low throttle than my car!

Have done the following:

Replaced injectors.
Replaced spark plugs
Coils less than 25K old.
Nearly new vacuum hoses.
Replaced Boost solenoids.
Replaced cam position sensors.
Replaced VANOS solenoids.
Replaced VANOS check valves.
Walnut blasting done 30K ago. (thx, cwarren )
Replaced both TMAP sensors (upgraded CP TMAP twice - to N20 with BMS cable, then back to stock - no change)
No boost leaks
Replaced throttle body to charge pipe gasket o-ring(more below)
Have tried multiple MHD tunes, including flashing back to stock stock.
Flashed Alpina transmission mod back to stock. No effect.
Smoke test reveals no leaks

Even tried changing burble options in MHD as they seemed to help another forum member...didn't really help me.

Car has mods but I assess they are not players.

CP now ER CP(no leaks). Problem existed with previous BMS CP.
DP's are now high flow catted c-PE. Problem existed with stock DP's.
MHD tuned, but have flashed back to stock stock with no change in behavior.
Have reset lamba/fuel/VANOS/Throttle adaptions with MHD multiple times. No effect. Did the "manual" throttle reset also. Some have said that using the ISTA/D software somehow resets differently and could solve my issue...but I haven't spent the $100 to try that yet. I guess i could poke around with INPA to see if it does the same thing.

Really running out of options. Last fewI have on my list are:

1. WB O2 sensors (I have em on my workbench, but job looks like a PITA - should have done with the DP's ) - DONE - NO EFFECT
2. Buy ISTA/D and see if it somehow resets differently than MHD. - GONNA TAKE TO DEALER AND UPDATE/RESET ALL ECU's
3. DME harness (Ug)
4. DME itself ($$$)
5. Throw away car and buy a new one

Problem really is small, in the sense that the car drives and pulls awesome most of the time and you can actually forget it exists...until you get in bumper-to-bumper traffic or drive around a parking lot for a while trying to find a spot. It is easier to manage in Sport mode as the revs are typically higher for a given speed/load.

Anyway, any help appreciated.

[LQQKOUT]

If you do a search, I know some people had one of the modules reprogrammed and it fixed the surging issue. Mine surges when I run a mix of E85.

[AndyW]

Originally Posted by LQQKOUT

If you do a search, I know some people had one of the modules reprogrammed and it fixed the surging issue. Mine surges when I run a mix of E85.

Yeah, I read some of those. Not sure which modules tho'. I have thought of taking it to BMW to have every ECU checked and updated to the latest software...but I imagine that will cost a pretty penny!

[pits200]

Originally Posted by AndyW

Yeah, I read some of those. Not sure which modules tho'. I have thought of taking it to BMW to have every ECU checked and updated to the latest software...but I imagine that will cost a pretty penny!

SurprisinglYa it doesnt. Most updates are just simple checkmarks that the tech chooses and they let it run. May take 8 hours to run all the updates but they usually will only charge for 2 hours give or take.

[Gohan335i7]

Any leaks of any kind ?

[AndyW]

Originally Posted by pits200

SurprisinglYa it doesnt. Most updates are just simple checkmarks that the tech chooses and they let it run. May take 8 hours to run all the updates but they usually will only charge for 2 hours give or take.

Thx. Guess I'll ask my SA for a quote. Can't hurt!

[AndyW]

Originally Posted by Gohan335i7

Any leaks of any kind ?

Nope. not that I can tell from visual observation or logs.

[tealslug]

I'm sorta on a thread over in the e90 section that is exactly on this topic (http://www.e90post.com/forums/showthread.php?t=483381). Unfortunately, no solid solutions over there either.

I've had many of the same things changed out that you list, and it still happens. Just replaced the "rear" DV with a new one (stock version), and the symptoms got a bit better, but have not completely gone away. So, given you've upgraded your DVs, I am thinking that while mine might have been bad (and somehow making it worse), it was not the source of the problem.

Search continues :-(

[AndyW]

Originally Posted by tealslug

I'm sorta on a thread over in the e90 section that is exactly on this topic (http://www.e90post.com/forums/showthread.php?t=483381). Unfortunately, no solid solutions over there either.

I've had many of the same things changed out that you list, and it still happens. Just replaced the "rear" DV with a new one (stock version), and the symptoms got a bit better, but have not completely gone away. So, given you've upgraded your DVs, I am thinking that while mine might have been bad (and somehow making it worse), it was not the source of the problem.

Search continues :-(

Actually...I have not replaced DV's..but those leaking at a vacuum should cause issues at idle.

Thx for linking the other thread!

[galahad05]

Vacuum leak. Maybe somewhere near your vacuum booster?


Wait, I guess someone else mentioned it already.

[AndyW]

Originally Posted by galahad05

Vacuum leak. Maybe somewhere near your vacuum booster?


Wait, I guess someone else mentioned it already.

No vacuum leak. Still have vacuum if I pull a connector 30 min after turning engine off. I also replaced all vac lines about 25k ago. I would also suspect a vac leak would cause issues at idle? The lack of an issue at idle really complicates this!

[galahad05]

I hear that. Is your idle speed normal? 650-700 rpm?
Sometimes an engine computer will see a rough(er) idle and correspondingly up the idle speed a bit.

[galahad05]

Also, I note that you messed around the throttle body--what about the throttle position sensor? If it gets dirty it could send...."sticky" signals to the DME on small throttle changes.

[AndyW]

Originally Posted by galahad05

I hear that. Is your idle speed normal? 650-700 rpm?
Sometimes an engine computer will see a rough(er) idle and correspondingly up the idle speed a bit.

Yep, idles fine @650 with AC, 550 without.

[AndyW]

Originally Posted by galahad05

Also, I note that you messed around the throttle body--what about the throttle position sensor? If it gets dirty it could send...."sticky" signals to the DME on small throttle changes.

Where is the sensor? The TB has been removed a couple of times for walnut blasting and such. I don't remember a separate sensor. Others have replaced the TB for this symptom with no luck so I stopped going that direction.

[galahad05]

I believe it is bolted right onto the side of the throttle body. Comes as a one-piece unit (sensor unit + throttle body).

I note that your data logs show TPS readings...

[AndyW]

Originally Posted by galahad05

I believe it is bolted right onto the side of the throttle body. Comes as a one-piece unit (sensor unit + throttle body).

I note that your data logs show TPS readings...

Ok, I was thinking you meant it was something separate...I'd have to replace the whole TB.

[galahad05]

I wonder if you could clean it instead.

EDIT: Understand this series of TPS is potentiometer based. That is, as the throttle is moved, the voltage reading various smoothly with the changes in position. At least the voltage is supposed to vary smoothly.
This can get messed up with dirty contacts, though, for example. They mess up the voltage measured by the computer. If there's a problem internal to the potentiometer, well that's a whole 'nother problem.
Just a possibility.

[AndyW]

Originally Posted by AndyW

Thx. Guess I'll ask my SA for a quote. Can't hurt!

$275 and I have to leave it for a day. If the O2 sensors don't work I guess it can't hurt.

[lightmanek]

I had similar issue with throttle hunting and jerky acceleration on low pedal input with my primary O2 bank 2 dead. Replaced it last weekend and now all back to normal.

[AndyW]

Originally Posted by lightmanek

I had similar issue with throttle hunting and jerky acceleration on low pedal input with my primary O2 bank 2 dead. Replaced it last weekend and now all back to normal.

Crossing my fingers. I'm replacing both O2 sensors today. I am assuming you had codes?

[lightmanek]

Originally Posted by AndyW

Crossing my fingers. I'm replacing both O2 sensors today. I am assuming you had codes?

Yes, sensor was knocked out during DP installation.