Unsafe engine revs between gears 3&4, 4&5, and shifting out of 5.

Hi guys. I'm new here, bought a 2007, 5-speed, 2.7L 4-banger, 4x4, 63,000 miles, excellent condition, a few months ago. I have this revving problem and have had it looked at by 4 different mechanics. I've had two TAS "supertechs" try to diagnose it and I've gotten the same bulls**t response both times, telling me this is "normal". Well, if this is normal and intended by design, then I'm selling the truck.

Their answer, Standard Answer #63528: "Condition is normal when at higher speeds ECM is to command the acell open values to increase by .5 degrees helping the rpms to stay up for a brief period of time to help when shifting."

So let's examine that "...helping the rpms to stay up for a brief period of time...". I notice this normal condition all the time, and yes, the rpms stay right about where they were when you pushed in the clutch (accelerator at idle position), for about 1 second. I see this during normal shifting at light loads and lower rpms (<2000). This IS normal and is NOT a problem.

MY TRUCK DOES THIS: When I shift from 4 to 5, lets say ~2400 rpm, and moderate load (mid-range acceleration) the engine revs to 3000 rpm, sometimes higher, and hangs there for 5 to 10 seconds! I have to slip the clutch (as you would in 1st, starting from a dead stop) because engaging the clutch normally causes the truck to jerk (you want the rpm to be ~1900). This happens EVERY TIME , is wearing my clutch prematurely and I don't have full control of the vehicle.

MY TRUCK ALSO DOES THIS: Picture exiting the Interstate after cruising at 70mph in 5th about 2500rpm. Press the clutch and the rpms go to 3000-3200 and will stay there for 10 seconds. If you engage the clutch during the 10 seconds, the truck will try to get back to 70mph! If you tap the accelerator, the rpms will go even higher and stay there. Don't even think about downshifting to get engine-braking.

MY TRUCK ALSO DOES THIS: Picture coming to a rather steep hill at 50mph, 4th gear. You want to maintain 50, so you press on the gas. At the top of the hill, you still want to maintain 50, and you take your foot off the gas. Guess what? The truck keeps going as if your foot was on the gas going up the hill.

There are other situations where the engine does weird things but this post is long enough. I can avoid the problem by keeping the load and rpms low (slow acceleration), but merging onto a 75mph Interstate isn't a good place to do that.

Toyota, at least at the Tech level, claims they've never seen this before. They certainly do not have a fix. The computer does not generate any "codes". They have done all the diagnostics (drive-along computer, etc.), cleaned the throttle body, and all the "normal" checks. As I said, four different techs have looked at it, and they're all out of ideas. Their "shotgun" approach is to replace the computer for $1200, but it's entirely likely this will not fix the problem, since they can't figure out what the cause is.

I've been trying to bump this up to the engineering level, but nobody seems to know how to do that, or they don't want to make the effort. I've got an appointment in a few weeks with another super-tech but I have zero confidence he'll be able to fix it. Winter is coming (I'm in Colorado) and I'm NOT looking forward to driving this vehicle on snow and ice.

Anyone else see this before? Comments welcome.

 

clean your throttle body.

 

OP - I have never heard of this and would not know where to begin. I know it's stupid but you're sure your gas pedal isn't getting stuck down in the carpet/floor mat right?

That gas pedal area is where I'd start to poke around. Maybe the mechanism that senses the pedal position has a problem and is sending bad values.

 

Maybe something funky is going on with the cruise control? Does the truck do this regardless if the cruise control activate button is pressed or not?

 

My first thought too. If you are in cruise and the upper clutch switch is faulty you that could cause this problem.

 

Obviously something with the throttle is sticking. Either gas pedal washer is worn (There was a recall for this), throttle body getting stuck, or throttle position sensor. Could be other things, but I would start with those.

 

First of all, thanks for all the responses!

Cleaning the throttle body was practically the very first thing the techs thought of, and did. Twice.
(Did I mention that FOUR certified Toyota techs have looked at this?)

Andrew: Yes, I originally described this as a "stuck accelerator pedal" or stuck throttle linkage to my mechanic. But a known-good accelerator assembly (pedal w/ sensors) has been put in and it has no effect. While it's revving, you can put your toe under the pedal and pull back, and the pedal is already all the way out. Also, I have diagnostic computer print-outs that show that the pedal is reporting "Idle position" and the computer is holding the RPMs at 2700-3000, with no actual load on the engine. So the computer knows the pedal is at idle but still holds the RPMs.

Road2Cycle & Jeffrey B: Yes, the cruise control was a suspect but the problem occurs regardless of whether the cruise control is on or off. The techs seem to discount the CC as a source of the problem. I don't know enough about how the CC works to argue with them. The upper clutch switch is working because if the CC is on and engaged and I tap the clutch pedal, it cancels normally.

Moondeath: The techs have cleaned, lubed and verified all of the mechanical linkages and have declared them working properly. They have concluded that the computer is holding the throttle open INTENTIONALLY but don't know why it thinks it should.

Here's some of my thoughts, I welcome comments/criticisms:

1) Automotive computer hardware rarely goes bad. And if it was a HW problem, it would occur in every gear, at every load but it doesn't. (I'm open to other thoughts.)

2) So it's a question of logic. So there's two possibilities.

a) the computer software has "dropped a bit" somewhere and causes the computer to make the wrong decision in certain situations. There are no SW "updates" available from Toyota, and one of the Techs wiped the memory and downloaded a clean version. Made no difference. But I suppose it's possible the memory that holds the SW has a bad spot, and the new SW was immediately damaged.

b) Garbage in; garbage out. My primary suspicion is that more than one of the sensors are faulty but the computer can't detect that, or somehow one fault cancels the other. One of the techs told me that "load" on the engine is a calculated-value based on the input from a bunch (not sure how many) sensors. My thought is that, based on the sensor values, the computer is calculating a (phantom) "load" and adjusting the throttle appropriately. Why it is ignoring the "Accelerator pedal at Idle" indication is a mystery.

Rather than shotgun the problem, I want to see my dealer & Toyota escalate this to the engineering level. An engineer who designed the computer HW/SW, or at least has access to the code, should be able to figure this out, or at least propose tests to determine the root cause. What do you guys think?

 

I don't know about the 2.7, but the 4.0 is drive by wire. So any of those sensors associated with throttle could be an issue. Even if the gas pedal repositioned to the correct spot, the sensor could still be sending wrong info. I highly doubt the computer is at 'fault', its just reacting to data received.

 

Yes, the 2.7 is fly-by-wire also. The computer knows the acc pedal is at Idle position, because when you take a snapshot during a reving incident, the computer confirms it.

One thing that's weird... so after reving for over 7 seconds, lets say at 3000rpm, with the pedal at idle and clutch disengaged (or neutral), sometimes the rpms will drop to 2500rpm for a second, then 2000, then idle (900). It's not smooth but like stair steps. So the computer is adjusting the throttle position based on some input that is slowly and discretely changing.

Oh, another thing, I've never been able to get the truck to misbehave just sitting in the driveway. You have to load the engine to get it to happen.

 

for shits and giggles, and i am not joking about what i am going to say below as this has a good posibility to help.

Get a 6ft length of decent AWG cable, say 12 or 10 awg wire. and two U shaped crimp connectors



big enough to hook to the ground terminal right on the inner fender by the battery (or the battery terminal itself).

Make a ground wire that goes from the main ground terminal right off the battery to one the four bolts of the throttle body itself, sandwiching the u shaped connector between the head of the bolt and the metal of the throttle body.

This will provide a MUCH cleaner ground and may help out reduce any EMI the TB is feeding back to the ecu causing these issues. Its worth a try and going to cost maybe 3 bucks and 10 min of your time.

 

Subbed...mostly out of curiousity

 

Subd

 

Interesting idea. I like it. I'll try to get this done today so I can test it and let you know. It'd be SO satisfying to tell Toyota.... ;-)

 

Definietly let us know if that helps. Its worth a try, easy and cheap.

It also very well could be a bad throttle body that works just fine 99% of the time and thus doesnt throw codes as everything is within spec.

 

Other than myself, you are the only other person on this forum (as far as I know) who's had issues with the revs increasing when pushing in the clutch and no throttle input.

https://www.tacomaworld.com/threads/2-7-l-4-cylinder-engine-rev-problems-issues.261943/#post-6401410

I had posted a bunch more than above post back in the early days (you can search), but no one would respond. It would most often happen on the 4th to 5th gear shift, and after travelling in 5th gear for a while.. Engine would rev to 3000-3200 rpm and hold for 5-10 seconds after pushing the clutch in and with foot off the throttle. I took it to the dealer several times to no avail. Changed spark plugs, cleaned TB and MAF, swapped PCV valve, etc. . . nothing. After a few months I learned that, after disconnecting the battery for an hour or so, things got a little better. Also, learned that the truck was EXTREMELY finicky with the timing of when you let off the throttle versus when the clutch is disengaged. You have to let off the throttle a split second before the clutch disengages, otherwise the rpms will hang or even increase. It took me several months to learn to time it just right, and after 4 years I haven't had any issues.

 

I subbed this because since I bought my 2010 Taco two months ago, I noticed when I was upshifting, the RPMs would climb when I pushed in clutch with no input from the accelerator. I didn't think it was normal but I had nothing to compare it to, having never driven a Taco before. I've driven standards pretty much since I started driving 45 years ago so driving standard shift is far from new for me. I may try the "pull the negative terminal off my battery to reset the ECU so it could "relearn" my style of driving" trick. Who knows, it might work. If not...I've been thinking about running it past the dealer to see what they think.

What are your thoughts all?

 

Its common on the 6 speeds for the rpms to hang between shifts. When I had the 6 speed it did this.

 

Is "common" normal though? It just seemed weird from the get go.

 

There is the common hang of rpms around 2k or so between shifts... but revving up when the clutch is pushed in is not normal.

 

The common hang is not only normal, the ECU is programmed to do it. Its an emissions thing. What the OP is describing is completely abnormal.