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Random acceleration

Over past year my dughter’s car (Honda Civic 1997 LX,air, cruise etc)would accelerate randomly. It happened about 5 times so far. It has been inspected twice by Honda dealers and once by another shop, nothing found. Highway driving with air conditioning ON over long distances, not a problem. When this problems occurs the following conditions are present:

Hot, sunny day

Air conditioning ON in STOP and GO traffic (traffic jams)

The RPMs will start gradually to increase over a few minute time span, and will climb up to 6000 RPM and will stay elevated until you pull over and shut car off

It becomes difficult to stop the car, breaks get hot, if you don’t pull over after a few mintues of this, car will BARELLY stop, once it happened in a school zone and she had to run the stop sign because breaks failed to stop car

Takes long time for car to cool down, and if you do not give it enough time to cool down will rev up again when turned on

Throlle cable and floor mate don’t seem to be the problem, cruise control not engage. Car drive normally no other problems. I would like to sell but would like to fix problem before selling. I would greatly appreciate any HELP.

I can’t explain why this is happening, but please tell your daughter to SHIFT INTO NEURTAL if it starts to accelerate out of control.

Fighting a wide-open throttle with the brakes is a good way to lose control and crash into something or someone.

Shifting to neutral will allow her to steer and stop safely, and the engine will not be pulling the car.

I would disconnect the cruise control cable and see if it makes any difference. Perhaps the cruise control is opening the throttle even though it’s not engaged.

I can’t help with the problem, but why in the world isn’t she putting the car in neutral in order to stop it safely?

You are not allowed to ask such a question,it implies we are dealing with

A malfunctioning Idle Air Control valve can cause uncontrolled acceleration.


The only thing that can make a car accelerate like that, in gear, is the throttle being opened, or sticking open. Disconnect the cruise control. Have a competent mechanic inspect and determine why the throttle is hanging open. It could be a frayed throttle cable, throttle linkage hanging up on something, throttle plate sticking in the bore. Consider replacing the throttle linkage and the throttle body.

You would think three mechanics would be looking at those issues. Can the IAC really flow enough air to bring the car to full power at 6000 rpm? what would tell the PCM to provide the fuel? the same failure that let the air in?

Yes. An IAC motor can cause uncontrolled acceleration. Just ask a buddy of mine who ran over a set of gas pumps when the IAC motor on his engine went nuts.

These IAC motors are linear stepper motors. Which means they can position the pintle at various positions depending on what the computer commands for the load on the engine. So in neutral at idle, the pintle is moved to one position. When the transmission is to put into gear, the pintle opens a little more. When the AC is turned on, the pintle opens a little more. When the power steering is used, the pintle opens a little more. If there’s a short in the windings of this stepper motor it can cause it to go full open allowing too much air into the engine. When this happens, the computer detects this excess air via the O2 sensor, and then adds more fuel to engine to compensate for this excess air, and the engine starts racing.


Good explaination Tester, I put a air intake bellows on a mid-80’s 7 series BMW and left my stall to use the restroom. The advisor came out saw the job done thought he would deliver the car. Well I had put the clamp on the wrong side and after one push of the throttle it pushed by this clamp so this engine was screaming at almost full throttle in the shop in reverse,at least the guy had the mind-set to shut down the engine. I told him to never again come and pull cars out of my stall without checking with me. There was he** to pay though. All this was going on while I was in the restroom,I came back,everyone looked at me, I said “what”? The stuff that happens in the shop,people would not believe.