25 ST-R - engine behavior bad

[crazydriver81]

Hi folks!

I need your help, because as usual I do not have a clue...

Yesterday, we completed the Brembo conversion and installed a new muffler. Parts changed in this connection were front ABS sensors, brake calipers, pads 'n discs and the rear muffler.

Today I took the car for a proper drive and noticed, that there is a problem with the engine now (was not there before Brembo's and Muffler!). Whenever you are above 2000RPM (regardless which gear) and you step off the accelerator pedal, the revs won't go back to the normal value of about 1200-1500RPM for AT cars. It feels like someone holds the accelerator pedal, although I am completely off the pedal.

1. you drive (e.g. 4th gear @ 90 km/h), all fine
2. you step off the accelerator pedal => the revs will stick where they are for a couple of seconds
3. sometimes the revs go down to mormal value, sometimes not
4. the revs are not constant, they alter within a range of 1000rpm

I recognized, that it got worse over the last 200kms. Any idea for the reason? Had diconnected the battery already, but no change...not even fault codes

Thanks für your help.
Stefan

[bradc]

Sticking throttle?

You could change the muffler back?

[MarkSanne]

If you experience this: can you pull the pedal back with your foot and will the revs come down? Maybe the cable to the throttle is sticky? (Seen it once before, quite scary).

[crazydriver81]

I have checked the throttle cable already and it's not sticky. Was my first thought too.

This happens only if you go completely off the accelerator pedal, if you tip it with one toe, no problems at all. This indicates to me, that the engine responds like it should when you hit the pedal. If the car is in stand still, no problems at all, neither with the revs nor with the response of the engine.

To describe the effect better...it feels like the gearbox wants to shift down. When you just roll, the revs go up a bit and normally you would expect the gearbox to shift down, but it wouldn't. After a few seconds, it seems to recognize that it hadn't shift down, so there is no need for higher revs and then it settles and go down to normal revs.

What I've recognized too, the INVECS gearbox does not "learn" my drivestyle anymore. It shifts from 4 to 3 at around 40km/h, although I used to shift manually at 60km/h.

[crazydriver81]

You could change the muffler back?

No, I couldn't because the flange is different. I would need a stock VR-4 muffler now...which I do not have.

[crazydriver81]

Does anyone know, from which sensor the AT gearbox recognizes the actual speed to check if it want's to shift? Possibly ABS sensors?

The more I think about it, the more I believe it has to do with the AT gearbox...

[steelie600]

there are two sensors on top of the gearbox that detect the shaft speeds

from front to back youve got gear position sensor (white with gear shift quadrant bolted thru it)
Input shaft sensor
Out put shaft sensor
road speed sensor (for speedo)

It may be worth pulling the codes to see if one has failed and also check all the sensors incase they have been broke or the wires have come off. I have the sensors if you need any

[crazydriver81]

will be going to the workshop in the next couple of minutes to check for failure codes.

[crazydriver81]

strange things turned out yesterday...

We spent nearly two hours to check all the sensors and engine readings with the MUT-II at the workshop.

Guess what...all sensors are working as expected! No failure codes. ABS sensors work as expected, gearbox sensor readings are fine.


It seems to be a problem with the gearbox itself. It feels like the gearbox could not recognize the shift points when in D mode, although the gear chages are smooth.

Maybe the gearbox could not check the oil pressure correctly? Possibly TC seal fail? How does it feel when the TC seal is on the way out? I have no idea, neither the guys from the workshop... HELP!

[GalantOnly]

Sorry to hear that, Stefan...

Worn TC seal will be throwing ATF under the car between the engine and gearbox. That's not what's wrong with your car... Did you check ATF level?

[crazydriver81]

Alex, my ATF level is correct. Oil is ruby red (Amsoil ATF / changed and flushed last year in autumn)

What I recognized is, that the car shifts down only at the minimal speed when in D (e.g. 45 km/h when from 4th to 3rd gear). This is usual only, if you are in TipTronic mode and forget to shift while slowing down.

The gearbox does not learn my drivestyle anymore. Normally, the TipTronic gearbox adopts your shift points from the Tip-Mode. Mine does not.

Additionally, the car shows a strange behavior with the revs, but only when you are driving.

e.g. when in fourth gear:
100km/h going off throttle - revs will stay at approx 2500, slowly going down
90km/h still off throttle - revs are at around 2000
85km/h still off throttle - revs are going up to approx 2250
80km/h still off throttle - revs are down to approx 1500

It seems to be something related to the revs, because it's nearly the same behaviour in 3rd gear (but at different speed). I believe something does not realize, that I am going off throttle. IMO this could be the gearbox input sensor only, but the MUT-II said that this thing works fine...

1. Which gearbox sensors are influencing the revs?
2. Any other ideas fellas?

Next idea is to check with a different ECU. Q has one available and he will it ship over from NZ. We'll see if my ECU is maybe fu**ed.

But anyhow, I am open to other ideas as I have no real clue about it.

[bradc]

Could you take a video of it?

[VR4WGN]

im sending 2 over ok,1 a nz new Manual ecu and 1 a st-r,thoguh i want the st-r 1 back ok,its for brads car lol... wooops dont tell himlol,,, ,sorry bradim sure there is 1 kicking around somewhere in the shop tho...

[crazydriver81]

Thanks Q, but I think the NZ manual ECU won't work because the ST-R ECU is engine AND A/T together. There is no separate ECU for the A/T gearbox...