2000 XC70 Transmission being funny on freeway...[ faulty brake pedal switch 9128577]

[FlyingVolvo]

Here we go...

A little background info:

- 162,000 miles on my car, original engine, original transmission.
- New XeMODeX ETM 13,000 miles ago, no issues.
- Transmission shifts very well up and down the gears.
- ATF has been changed often, is very clean, and at perfect level.

Coincidence:

- 2 days ago I installed a new intake pipe ("sconeman"/snabb pipe, popular on VolvoSpeed).
- 1 day ago attached a clamp-on K&N cone filter

Problem:

I was driving on the highway today, and while at 65 MPH and about 2000 RPM, suddenly it seemed to drop out of overdrive as if I had pushed the pedal hard to downshift. The RPM shot to about 2500, then after a few seconds, they went back down. This happened several times.

I sped up to 75 MPH and the engine was racing but the tranny did not want to lockup until I let off the gas just a tiny bit. It then bounced back and forth out of lockup a bit like before. I was driving on some rolling hills, but the behavior was definitely abnormal.

FYI: There was NO flashing up arrow or check engine light while any of this was happening.

Reasons?

I talked to Justin and we thought of some possible scenarios...

1. Transmission is losing overdrive lockup capability and slipping.
2. New intake = little more power, especially on freeway. Maybe computer is confused?
3. Something else electronic making the car think it needs to downshift.
4. ???

Justin noted that it's unusual for a transmission to be slipping out of OD like that without the flashing arrow. He also suggested I try and go into cruise control and see if the same thing happens. I think I will pull the battery tomorrow to reset computer as well.

Help! I gotta home in a few days...

[kcodyjr]

Certain you didn't knock anything loose when you were installing your new intake?

Have you actually lost cruising power due to your new intake being more vulnerable to heatsoak? This would be a bigger problem at low throttle than high, so it may well be more powerful when you're into it, but not under a light foot.

All else being equal, more power should encourage lockup, not hinder it. It unlocks when the engine can't provide enough torque directly; that is, when it would begin to lug.

That draws attention to a clarifying question - are you slipping out of OD, or is the torque converter unlocking, or both?

Watch your RPM numbers carefully and keep checking in with butt-sensor. The difference can be subtle.

[Red-Arrow]

This problem has nothing to do with the intake imho.

Unless its throwing your AMM off? unlikely but maybe.

[jblackburn]

It sounds to me like the torque converter is locking and un-locking for no reason.

My thoughts were a electronic throttle pedal position sensor making it think it needs to downshift, but I don't know the newer (99-2000) models all that well.

This sounds kinda similar to what mine kept doing when I was coasting last summer - I never did figure it out, but it stopped doing it.

[kcodyjr]

A behavior change due to the intake is no less wacky than the computer being confused about being too powerful, IMO.

Still, I agree, it isn't likely.

Knocking a wire or vacuum hose off while installing the new tubes is something else entirely...

We need more of that butt-sensor output to determine whether it's an OD problem or a torque converter problem.

From the numbers alone, 2K to 2500, I tend to think torque converter; a drop to 3rd should put you higher, I'd think.

Justin, yours looks more like the overdrive, you were kicking from 1500 up over 3K.

[jblackburn]

That's when I stepped on the gas to get back up to speed

At the end it was fluctuating back and forth; I think it was going from lock-up to not and back again.

You could also try checking out the pins on your transmission controller if it's shorting or something - though I kinda doubt it's that. Mine looked brand-new.

[jimmy57]

MAF sensor is HUGELY responsible for load signal TCM uses for shift control. Put the stock air cleaner back on and see if the problem is resolved.
I am driving a 99 S80 T6 that belongs to my sister. It has had lots of strange trans misbehavior and shuttered often while shifting. Being a GM trans I pretty much assumed it needed a trans. The check engine light came on for fuel trim code and I fault-traced that and found nothing other than the short term fuel trim was off in lower part load range. I put a known good used MAF sensor I have on it and fuel trim issue causing CE light was fixed and trans has been behaving perfectly since. I was not buying the MAF fixes trans thing so I put the old back in and the trans shutter came back. Good MAF back in the car, trans shutters at low throttle shift gone instantly.
I have seen very minor irregularities like a blade of grass on MAF screen upset MAF sensor's signal. The new air cleaner could be an issue and is the easiest to eliminate.

[FlyingVolvo]

Certain you didn't knock anything loose when you were installing your new intake?
Have you actually lost cruising power due to your new intake being more vulnerable to heatsoak?
That draws attention to a clarifying question - are you slipping out of OD, or is the torque converter unlocking, or both?

All vacuum hoses are on securely. When I was driving earlier, the temp was just below 40 degree F. At highway speed, I don't think heat soak would have been an issue. I'll be building a custom heat shield too when time permits.

As far Overdrive vs Torque Converter, I don't really understand the difference. Is "slipping out of OD" basically going to 3rd gear? And torque converter locking/unlocking would mean staying in 4th gear, but with or without lockup?

The change in RPM not crazy significant, but noticeable. Butt dyno felt the change.

MAF sensor is HUGELY responsible for load signal TCM uses for shift control. Put the stock air cleaner back on and see if the problem is resolved.

I have seen very minor irregularities like a blade of grass on MAF screen upset MAF sensor's signal. The new air cleaner could be an issue and is the easiest to eliminate.

I'll definitely give that a shot. However, I should also note that my MAF is less than 3 months old (Bosch). If by some miracle this is fixed by changing to stock air cleaner again, I guess I'll be able to attribute it to either the K&N filter sending rough air to MAF, or there is the whole deal with the K&N oil perhaps messing with the MAF.

[jblackburn]

Uh oh, you didn't oil your new filter, did you? The oil is a known killer of MAF sensors.

4th gear engages around what, 35 mph or so? Then you get "lock-up" where the torque converter stops slipping and matches the engine - wheel speed at around 55 mph. It feels like an extra shift, a 5th gear if you will.

[kcodyjr]

Quick thought, did you reset your ECU after installing that intake?

You know, disconnect the battery, then foot on the brake, tap the starter, to eliminate any remaining power; then have a beer or a smoke, go get a coffee, otherwise kill about 15 minutes, then reconnect?

Any help folks, whether that particular reset (fuel map?) is applicable here?

+1 if you oiled the new filter. They come pre-oiled.