creeping tach while on cruise

[riverwolf]

I've got a 2K3 V8 LTD 4wd. Just got back from a 600ish mile road trip. Noticed at times, while on cruise on relatively level ground for an extended period of time that the tach seemed to creep up. Say I set the cruise and the tach needle was just barely touching the high side of the 2000 rpm indicator block...after 20-30 minutes the needle was about 1/3 the way to the 2500 tick mark. Speedo holding steady where set and MPG computer also unchanged. If traffic caused me to break cruise and then resume, the tach would go back to the initial 2000 block. Sometimes it would then creep back up towards 2.5k, but not always. Never was able to actually catch it moving.

First time I saw it, I wondered if tranny had downshifted to climb overpass or something and then hung instead of upshifting, but bumping down to 4th manually confirmed that was definitely in 5th the whole time.

Anybody ever see this behaviour? Normal tolerance since we're potetially talking about maybe 250-300 rpm variance? Nothing else felt or acted funny, but should I have anything check out by dealer?

Thanks.

Brent

 

[Iowa4Runner]

I've got a 2K3 V8 LTD 4wd. Just got back from a 600ish mile road trip. Noticed at times, while on cruise on relatively level ground for an extended period of time that the tach seemed to creep up. Say I set the cruise and the tach needle was just barely touching the high side of the 2000 rpm indicator block...after 20-30 minutes the needle was about 1/3 the way to the 2500 tick mark. Speedo holding steady where set and MPG computer also unchanged. If traffic caused me to break cruise and then resume, the tach would go back to the initial 2000 block. Sometimes it would then creep back up towards 2.5k, but not always. Never was able to actually catch it moving.

First time I saw it, I wondered if tranny had downshifted to climb overpass or something and then hung instead of upshifting, but bumping down to 4th manually confirmed that was definitely in 5th the whole time.

Anybody ever see this behaviour? Normal tolerance since we're potetially talking about maybe 250-300 rpm variance? Nothing else felt or acted funny, but should I have anything check out by dealer?

Thanks.

Brent

If you were going up a slight incline or into a headwind it was probably your torque converter unlocking, which is normal.

 

[riverwolf]

Once it crept up, it stayed there for many miles/minutes until I was forced to break the cruise for traffic. If it was the torque converter unlocking, it never relocked. The terrain was relatively flat, nothing that the V-8 should even blink at when holding 70 mph...I-95 South from Richmond area to Raleigh then I-40 to Wilmington. FWIW, we stopped for gas/bio-break in Roanoke Rapids/Weldon and the RPM creep didn't reappear for the remaining 180 miles...rebooted?

Any further self-diagnostics I can do to test for torque converter problems?

wbs

 

[Brewster]

Riverwolf:

I posted the following this past Feb., and never got a reply.
---
"Does anyone have any trouble with the torque converter staying unlocked when it shouldn't?

I do a lot of driving on west Texas I-10 (75 mph speed limit), and I like to use the cruise control. Many times I have caught the tach reading about 200 RPM too high. If I turn off cruise control and then reset it to the same speed, the revs then stay normal until I get tired of watching the tach. Then, maybe 50 miles later I'll notice the revs have jumped again.

It looks like the converter might be unlocking on an uphill grade, and then not relocking when the road is level again."
---

A few days ago, I watched the tach carefully on a 70 mile highway trip at 65 mph. When the converter unlocked due to an uphill grade, it would apparenly not lock again until I switched off cruise. That is, once it unlocked, it would settle down about 100 rpm above what it had been. When I canceled cruise, used the accelerator pedal carefully to get the speed & tach readings back where they should be, and then reset cruise, everything would be fine until the next uphill grade. During this trip, the converter NEVER relocked while on cruise. (All this assumes that this is not some strange tach glitch.) I don't know why it was 100 rpm this time, rather than the 200 rpm I reported before, except that I was going 10- 15 MPH slower and was less heavily loaded.

I had the dealer check this during my 30K service last week, but their diagnostic computer check didn't show any error codes. I intend to go back and demonstrate the problem to one of the senior mechanics.

 

[Iowa4Runner]

I intend to go back and demonstrate the problem to one of the senior mechanics.

I wouldn't waste the time. This apparent torque converter problem is just one of many issues Toyota's engineers overlooked when they developed the control algorithm for the transmission. I doubt the dealer could to anything to change it.
I'm starting to wonder if Toyota test drives their prototype vehicles before they go into production. If I had time I'd go to school on this transmission and make my own freaking controller and get this thing to shift correctly 100% of the time instead of 90%. :upset:

 

[Koz]

You have to remember that this trans has electronic intelligence that will keep the trans from up shifting when idling downhill. There could be a problem that has something to do with this. I will simulate the conditions you describe and let you know if mine does the same thing. I doubt the engineers missed this, it's probably an adjustment. The problem is the dealer will not take the time and effort to simulate the problem; you may have to physically show them.

Koz

 

[toys4life]

Does Toyota use a variable apply torque convertor like domestics do/did? The system would vary application of the convertor based on load conditions (grade, headwind, etc...), not just 0% and 100% apply.