This "unintended acceleration" business...

No, I haven't experienced it, and my complaint is minor, but this is what I do feel:

First my 09 Tacoma is a V6, automatic 5-speed, and it's not broken in yet. I have maybe 200 miles on it of which 175 is stop & go traffic on the main boulevards here. that means traffic gets from 0~45 MPH and back to zero every couple blocks.

When I'm slowing to a stop, I can feel the engine accelerate a little as the truck slows down, and suddenly the brake pressure I'm applying isn't slowing the truck quite as much as it was. Instead of tapering off the pedal I'm having to push harder at the "middle" of a stop, because the engine's pulling me just a little when it should be braking me more and more (as manifold vacuum rises.)

Because of this I've taken to shifting the trans down manually, which is less smooth, but I get a more steady and controlled feel under braking.

I'm suspecting that the smog controls are bypassing some air to the intake to prevent a richening of the mix as the trans shifts down, but I'm not sure I could tell that even with a manifold gage.

I've had other auto trans cars do this (though much worse) when they developed a minor vacuum leak or a balky idle air bypass motor/solenoid.

As I said, it's minor, but certainly annoying. If it doesn't clear up a bit as the truck starts to get broken in, I'll probably take it in and complain to the dealer.

 

A/C on?

 

Yes, AC

 

Yeah, I live in the desert. It's been on almost 100% of the time since I bought the truck.

So are you telling me this happens because the A/C clutch kicks out as I'm slowing down? Every time I come to a stop? Seems kinda strange. As you slow down the A/C has to work harder because of less airflow and less compressor RPM. I'd think the A/C would tend to kick in as I slowed down.

OK, it's gonna be 102 today. I'll go try it without the A/C and see what happens.

 

No AC! your an animal.......Wait till the evening to try it.

 

don't think it's the tranny.... try the AC first to rule it out! then if this is a consistent problem take it to the dealership and let them know you feel that the vehicle is unsafe and could pose a danger to you and the public. if they can not resolve the issue call toyota

 

That is the general consensus, yes.

 

^I used to think that but I, and many others, simply don't have it with the A/C off. Not that I'm doubting you but are you sure it's off completely?

 

^See, that's the other theory, that it's an a/t pressure issue.

 

Ummm...why not just tap a voltmeter into the compressor clutch circuit and see when it kicks up and down?

 

I could definately see that happening, but with this fly-by-wire business I have no idea what's actually happening to the throttles. Again I think the ECU could be bypassing air to help burn off emissions.

 

I will try the A/C first. In fact I'm going out to do so directly.

So far I do not feel the vehicle is unsafe. I can certainly stop it. I just don't seem to be able to stop it as smoothly as I'd expect a Toyota to stop, due to this issue.

 

OK I'm back from my test ride, and what I think is actually happening is this:

First, it is only noticible under very light braking, when coming slowly to a smooth stop. I haven't made a panic stop yet, but under even middling moderate braking pressures the effect is undetectable.

As I'm slowing I'm getting pretty normal (for an automatic) engine braking in 3rd gear, but then as it shifts down to 2nd there's a long pause where it feels like the truck is coasting with no engine braking at all, until it slows almost to a stop. It's at the point where the truck starts to coast that I have to apply the brakes harder.

Also, I do notice much less of this effect when I switch the A/C off. It still happens but is far less pronounced. In fact if I wasn't actually looking for it to happen I probably wouldn't have noticed it at all.

 

I felt the same thing when I first got my 09. I notice it most under light braking and I think it just may be how the transmission is downshifting at higher RPM's. I had a 94 Mustang with a shift kit in the AOD and it used to downshift much harder than the Tacoma so I am relatively used to it. I'm by no means a mechanic but I think that it's just the transmission downshifting. My way of thinking about it is that if it weren't supposed to do it, then my truck wouldn't have made it out of the factory.