Toyota acceleration

toyota
tacoma

#1

In light of the Toyota problems I have a question somewhat related. I have a 1999 Toyota Tacoma two-wheel drive pickup truck.



When I have the windshield defroster turned on and slowing down for a stop or just moving slowly in traffic, suddenly the engine speeds up just enough that I need to apply more pressure on the brake pedal and of course there is a slight acceleration which has made things a little dicey at times and has almost made me bump into my garage, the auto in front of me, and though not that close, even people in the cross walk while slowly coming to a stop for the cross walk.



I realize this is probably the air conditioner kicking in for the defrost mode but it seems to somewhat be a little over compensating and could cause an accident.



Should I join in the Toyota acceleration problem or is this normal?



Thanks,



Stan


#2

This is normal operation of the Idle Air Control valve as it attempts to hold the idle speed as commanded by the ECM. Due to the light load caused by the low outside air temperature and the resulting low temperature of the A/C condenser, the ECM over compensates for the perceived load increase. The only way to correct this problem would be a software modification that took into account the actual load the A/C compressor is putting on the engine.

Your problem does not rise to the level of the unintended acceleration of the later model Toyotas.


#3

Your truck does not have the “accelerate by wire” system that’s causing all the recalls.

I agree with Researcher’s explanation of the ECM adjusting the idle speed via the IAC to compensate for the added load, but it sounds to me like yours may in fact be overcompensating.

Do you have a tach? Does the engine speed bump up when the compressor engages? How high?
Try it in neutral and see how high it jumps.


#4

Thank you for your reply and the detailed explanation.

I agree with you its not what I hear in the news about the acceleration problem but it is something that could cause an accident and believe me, it can catch a person off guard as it did myself a few nights ago while backing into my garage which prompted me to find a website such as this one to request other opinions.

I like the truck and it runs great with 160,000 miles on it but this is a bad design.


#5

Thanks for the reply and I agree about the previous reply from Researcher but it is another acceleration problem with Toyota though not the same caliber as the one making the news these days.

The truck does have a tach and it does bump up alright, I’ve noticed it while in park position and the compressor kicks in, I will have to give it more attention to see just how much. This problem is not noticeable while driving at highway speeds, its only apparent at very low speeds.


#6

I have a '98 Taco and it does the same thing. I agree with sgrams’comments to the the folks addressing the stated problem. Whether or not it’s been recognized by Toyota as a “dangerous” problem dodges the question, it is a horrible design. I’ve had dozens of autos that all have idle up mechanisms to compensate for the compressor, but none could actually push you forward from a stop at a red light. You don’t need a tach to determine that your vehicle is accelerating -or as one poet once put it, "you don’t need a weatherman to know which way the wind blows."
I think what would be most helpful is more specific information about “a software modification that took into account the actual load the A/C compressor is putting on the engine”. Does this information exist or was it just pontification?


#7

Thanks monkeywrenchsc, its been a bit since I checked back here, it would be nice to have more specific information alright, and what is the cost if there should be a fix, I think it should be done for no charge. From the lack of more responses it doesn’t seem to be much of a problem for others but I appreciate your response.


#8

I can tell you what Toyota’s advice would be; Practice turning off your air conditioning and leave a car length between you and the car at the stop light and/or the person in the crosswalk.

On a more serious note, my 96 T100 had the same symptom, but after I traded up and bought a 2002 Tundra, I noticed the problem was gone. Maybe they’ve fixed the problem in later models.


#9

My dad’s '99 Tacoma does the same thing. Luckily it’s a standard shift, so it’s typically out of gear when idling. For us it’s more annoying than dangerous, as sometimes the rpms drop back down right when you’re letting the clutch out to go- so it’s easy to stall if you’re not on top things and adjust gas pedal pressure.

It’s just one of those quirks that many (most?) vehicles have…especially older ones, but it’s liveable; and after driving the vehicle for a little while, compensation for it should become second nature (like checking mirrors, etc…). In my case, I’ve learned to giver a bit more gas when I’m letting the clutch out. In your case, a bit more pressure on the brake pedal is probably the cheapest and easiest resolution. …and probably more than any “fix” you’ll ever see from Toyota about a 10+ yr old vehicle. I suspect they’ve got their hands full right now.


#10

Has this been a problem sense new, or has this problem developed over time.


#11

Thanks for the reply, I understand what you are saying when using a clutch, starting out on a incline could be difficult, that would be annoying alright. And, more caution is necessary but its still a bit dangerous when pulling into a parking space or other tight situation. I will be keeping the truck for a while yet because of my budget and the truck runs well, I now understand its not just my Tacoma.


#12

Thank you for your reply. Its good to know the problem was addressed with later models. I noticed yesterday, while coming to a stop the engine revs up about 200rpm’s, that is the amount it dropped down anyway because I was still moving when it accelerated but stopped when it slowed down so I could watch the tach.


#13

This is not a new problem, I bought the truck used about 4 years back. I realized when it first happened what was going on and I thought it seemed a little dangerous but now with this news of an unrelated accelerator problem maybe its something that should be addressed. I now realize other Tacoma’s also have this issue but it seems to have been rectified in later models.


#14

Thank you everyone for your posts, now I know why and what is happening, I doubt I will find any help from Toyota with this issue but it sure helps to understand it.