Rev hang on warm up

[Suhb]

Here is a video of what the title refers to.

On the first 3-4 minutes of driving after a cold start, the car exhibits really bad rev hang. To the point that I have to wait almost 2 seconds between each shift. It happens on every start up and I can't for the life of me figure out why.

Car has had vanos solenoids cleaned, then replaced. Eccentric shaft sensor replaced along with valve cover followed by a smoke test to check for a vacuum leak. There is none. Cleaned the maf sensor.

I want to suspect that it's the maf or O2 sensors, but isn't the car on a closed loop on start up? Anyone have any idea or experienced this?

[rjahl]

Originally Posted by Suhb

Here is a video of what the title refers to.

On the first 3-4 minutes of driving after a cold start, the car exhibits really bad rev hang. To the point that I have to wait almost 2 seconds between each shift. It happens on every start up and I can't for the life of me figure out why.

Car has had vanos solenoids cleaned, then replaced. Eccentric shaft sensor replaced along with valve cover followed by a smoke test to check for a vacuum leak. There is none. Cleaned the maf sensor.

I want to suspect that it's the maf or O2 sensors, but isn't the car on a closed loop on start up? Anyone have any idea or experienced this?

Plug in INPA and watch accelerator pedal, eccentric cam and engine loads. That should give you an idea towards the cause.

Couple of good logging tools available right now as well.

Will it hang up like this while stopped and in neutral?

[Suhb]

Not really sure how to see engine loads or eccentric shaft readings, or what to look out for if I find them.

I do see accelerator pedal reading and it is at 0%. Car exhibits the same behavior in neutral while parked.

Car in the past showed up the error codes:
2F83
2F81

Couldn't find what they mean though. It says unknown error description.
Might be from the recent coding I was doing on the car but not sure.



Something else I noticed while digging around in INPA.

Car shows the oil level reading while the oil temp was still around 50 Celsius. This shattered my world views as I used to use the oil level reading to check if the car was up to temperature...

[chris_flies]

I'm pretty sure that the car doesn't engine brake when cold. Going down a hill where it would normally display 99.9mpg it was showing 30-something. This probably relates to the rev hang issue...

[///Makis]

Originally Posted by Suhb

Here is a video of what the title refers to.

On the first 3-4 minutes of driving after a cold start, the car exhibits really bad rev hang. To the point that I have to wait almost 2 seconds between each shift. It happens on every start up and I can't for the life of me figure out why.

Car has had vanos solenoids cleaned, then replaced. Eccentric shaft sensor replaced along with valve cover followed by a smoke test to check for a vacuum leak. There is none. Cleaned the maf sensor.

I want to suspect that it's the maf or O2 sensors, but isn't the car on a closed loop on start up? Anyone have any idea or experienced this?

I can't see the video, but I'm assuming you have an auto and my car does it as well. I believe it's the transmission. When the fluid isn't warmed up the first couple shifts either hang between changes or it revs unusually high before changing and sometimes clunks between up shifts.

I've also had a few abrupt clunks on downshifts going downhill and braking.

I assume once you've been driving for about 5 min or so it gets better and no longer does that correct?

I changed my tranny fluid about a month ago (at 46k miles) and although the hang is still there, it's nowhere near as bad as before.

I believe there is a company called sonax that makes a kit for the 128i GM transmission to fix this. They actually have a few kits to fix various problems in the transmission I think this one in particular is called the zip kit but I'm not 100% sure. You can find a bunch of videos of people doing the install / mod and if you see the hardware compared to OEM it definitely looks like it's better quality.

If you're over 50k miles And have never changed the transmission fluid, I'd start there and see if it helps. If you can change the engine oil, you can do this, but it is a PITA being under the car and dealing with all the bolts as well as the fill procedure so do your research if you decide to go this route. Personally it was a mistake on my part to do this in winter, so I'm
Not sure if you want to go down that road now.


M

[Suhb]

Hey Makis, thanks for your experience. I'm sure some of the auto guys might find it helpful to change their auto trans too.

I actually have the manual. I realized that it's likely the cat warm-up sequence where it's still dumping fuel to get the cat warmed up.

I noticed the pronounced rev hang right after I reverted back from catless headers which required a tune with no cat heating sequence, so no rev hang.

I just learned to live with it and shift accordingly until he car is past the warm-up phase.

[///Makis]

Originally Posted by Suhb

Hey Makis, thanks for your experience. I'm sure some of the auto guys might find it helpful to change their auto trans too.

I actually have the manual. I realized that it's likely the cat warm-up sequence where it's still dumping fuel to get the cat warmed up.

I noticed the pronounced rev hang right after I reverted back from catless headers which required a tune with no cat heating sequence, so no rev hang.

I just learned to live with it and shift accordingly until he car is past the warm-up phase.

Oh I see what you mean with rev hang.

Yeah that makes sense.

Out of curiosity, why did you change back to catless?