My 89 L98 has a TPS connected to the ECM. I'm wondering what might happen if the TPS (probably just a pot) failed short/open - what would happen? Runaway or stop?
Ditto for the ECM throttle logic. Runaway or stop?
Just thinking ahead here.
The TPS would set a fault code and illuminate the MIL, the throttle blade is still connected to the pedal by a cable so there would be no runaway. Once the ECM sees a voltage outside of normal limits for a sensor such as TPS it is ignored, and the ECM then uses remaining inputs such as MAP or MAF as substitute, essentially in limp in mode until the fault is cleared.
The Toyota cars in question and many newer cars including Corvette have no physical connection between the pedal and throttle blade, commonly called "drive by wire". The throttle pedal sensor sends a signal to the PCM which then activates a throttle control motor to open the throttle blade.
I suppose if the return springs broke on a throttle body or carb for that matter, and you have just put the pedal to the floor and gets caught on the floor mat, it would make for some excitement. Other than that, no runaway.
There is no question that all C4s have a direct mechanical connection for the brakes, transmissions and ignition systems.
If the throttle stuck open for any reason and the engine actually ran wide open - shifting to nutrual, stepping on the brakes or truning off the ignition would all work to stop the car.
The only TPS problem that I have ever seen is it wears where you normally use it and it will get a dead spot and you must back off or push throttle open more to keep it going but when you take your foot off the throttle it will return to idle.
Like posted above the throttle spring would have to break for it to have uncontrolled acceleration.
The bad thing is if this happened on a Corvette it would not take half a day to attain 90 mph as it would in a Toyota.
TPS is not a coil capable of generating enough electromagnetic energy to twist the throttle shaft. Its just a measuring device. There is no other mechanical link.
Newer yr vettes with traction control features DO have a ECM link. They have a throttle controller thats used to back off the throttle when a loss of traction is detected in a drive wheel. This is done by a drum that has cable rolled up and operated by a motor that gets its signal from the ecm.
Regardless, cool heads prevail. Anyone that just sits there while their car accellerates to warp 7 in a grocery store parking lot almost does'nt deserve to have a license IMHO.
All it takes is a simple turn of the key, in gear or out. Worst case, shift out of gear and let the motor blow, if it will.
My BBK throttle body WILL stick when it gets dirty and yes, its always a surprize but its SO easy to end the terror. Just tapping on the gas pedal releases it.
On my first vette (1988) I washed the engine area not covering any parts. Trying to be careful, water still had gotten into the TPS. When I drove the car, it had random spikes in RPMs. No issue in controlling the car. It just drove like crap. Check engine light came on indicating a TPS voltage out of range. As stated above, the ECM doesn't control the throttle valve, so we are not so dependent on computers as newer cars. I had a holley 4 barrel stick almost wide open on me, but that issue was repeatable enough to correct in minutes.
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