Unintentional Acceleration in 1994 Toyota Corolla


#1

Our daughter drives our 1994 Toyota Corolla DX sedan in the Atlanta area. Until this week, the car occasionally had UA–unintentional acceleration. This week the car began going full throttle with no pressure on the pedal as soon as the driver let off the brake. This happens in drive, reverse, neutral and park. Though the brakes work and stop the acceleration, it’s dangerous. Today her mechanic (seems like a good guy) changed her throttle position sensor ($178) and the idle speed con. sensor ($285). The car worked for two short drives and then did the same full throttle. We’ll take it back tomorrow, but thought you might have advice.



One more point: the car has an add-on cruise control.



Previous Q&A attributes similar problems to a groove in the throttle body (1993 and 1989 Camry wagons) and the add-on cruise control (2002 Echo). The Camry Q&As give advice on how solve the problem with adjustments to the curb idle speed screw and air bleed screw.



We’d appreciate any ideas.



Thanks!



--Alan


#2

Disconnect the cruise control from the throttle linkage. Now. Before the car is driven again. Why the mechanic didn’t do this immediately is beyond me.


#3

First, thanks for your advice. Second, why do you recommend this step? Are add-on cruise controls often a problem? Alan


#4

One step forward, two questions back. 1. You have to start somewhere and step one and two have been done already. 2. Yes. Would you rather do the cheapest thing or start by replacing the computer?


#5

I agree with NYBo of course about disconnecting the the cruise control servo cable to see if the problem goes away. A long time ago I used to install a lot of aftermarket cruise controls but I don’t know if I’m familiar with the unit on this car or not because there are a number of different cruise manufacturers.

Some control modules had several adjustments on them and it’s possible an adjustment gone stupid could be causing this. The adjustable ones had a low speed activation switch, centering switch, etc.

One thing that should not be done is dink around with the curb idle screw and air bleed screw in an effort to override this problem. That can open up a can of worms also.


#6

We’ll do the step that you two recommend–disconnecting the after-market cruise control. We’d have done that first if we’d have gone to this discussion group first. We bought the car used in 2000 with the cruise control in place, but we would not have known better anyway.

It’s got to be obvious that we don’t know much about cars or what to do–and haven’t since owning a 1972 Plymouth Duster. We appreciate your help. Alan