Sudden unexpected acceleration -HELP (1 Viewer)

[earlsquirelson]

Hi all,
While driving our old 1fz-fe 80 series, my wife experienced a genuine sudden unexpected acceleration event. Trouble shooting the issue has eliminated floor mats, pedal issues or throttle cable issues.

Removed the throttle cable from the car, and feeling the throttle valve spring shut when opened by hand.

Starting the car, the engine ignition starts up ok followed by a loud knock sound and the engine suddenly hits the rev limiter.

Any ideas on what’s causing the issue would be appreciated! Thanks.

 

[Marvelicious]

The 80s aren't "drive by wire", so those issues are out. Even a stuck injector would tend to bog down without extra air to match, so something opened your throttle or provided air somehow. Meanwhile, something providing that much air would still need the fuel, so something activating the throttle is the most likely culprit. I'm not accusing your wife of anything, but I'm kinda stumped aside from "user error". By the sound of it, she just fired it up and didn't touch the throttle? There are three cables attached to the throttle, so I suppose it could be some sort of malfunction in the cruise control system, or somehow the transmission kickdown cable? I'm just spitballing because it's an odd occurrence.

This is weird.

 

[IdahoDoug]

Just re-confirming this is NOT a diesel, correct? I'd again disconnect the throttle and cruise and tranny kickdown cables, then start it and see if it idles as normal. I'd have someone else do it (and be ready to shut it down) because I'd want MY hands on all 3 of those cable ends to feel if one of them suddenly tugs. Very unusual.

 

[earlsquirelson]

The 80s aren't "drive by wire", so those issues are out. Even a stuck injector would tend to bog down without extra air to match, so something opened your throttle or provided air somehow. Meanwhile, something providing that much air would still need the fuel, so something activating the throttle is the most likely culprit. I'm not accusing your wife of anything, but I'm kinda stumped aside from "user error". By the sound of it, she just fired it up and didn't touch the throttle? There are three cables attached to the throttle, so I suppose it could be some sort of malfunction in the cruise control system, or somehow the transmission kickdown cable? I'm just spitballing because it's an odd occurrence.

This is weird.

Issue still occurs with no pedal (no throttle cable) it’s persistent and occurs every time the car starts

 

[earlsquirelson]

Just re-confirming this is NOT a diesel, correct? I'd again disconnect the throttle and cruise and tranny kickdown cables, then start it and see if it idles as normal. I'd have someone else do it (and be ready to shut it down) because I'd want MY hands on all 3 of those cable ends to feel if one of them suddenly tugs. Very unusual.

Not a diesel, cruise and throttle cable (connected at the pedal) are out of the vehicle. I’ll check the kick down cable, thanks.

 

[DivByZero]

Issue still occurs with no pedal (no throttle cable) it’s persistent and occurs every time the car starts

Your car is possessed. You need a priest, crosses and holy water.

Seriously, no idea what's happening to your rig, but I'm curious to learn what the cause is. You mention a loud knock sound. Any idea where that's coming from?

 

[ChargedSHOTaco]

I'd check that the Idle Speed Control Valve is working properly.

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[60 toy ota]

Is your butterfly valve properly connected to the shaft and in good shape?

 

[GORDA91]

I’ll be happy when my 3fe suddenly accelerates!

 

[earlsquirelson]

Your car is possessed. You need a priest, crosses and holy water.

Seriously, no idea what's happening to your rig, but I'm curious to learn what the cause is. You mention a loud knock sound. Any idea where that's coming from?

It does feel possessed! Time to start pulling the throttle body off to see what I can find

 

[earlsquirelson]

I'd check that the Idle Speed Control Valve is working properly.

​

Pulling idle control valve and tps sees same issue persisting although I think maybe no iscv valve might be the same as having a wide open throttle (big hole on the side of the throttle body)

 

[DrDuc]

Did you name your car, Christine?

I hope it turns out to be a simple fix.

 

[jonheld]

Starting the car, the engine ignition starts up ok followed by a loud knock sound and the engine suddenly hits the rev limiter.

What year?
The 1FZ-FE doesn't have a "rev limiter".
What you're describing would be indicative of a diesel motor's injector pump malfunctioning.

 

[landtank]

Sounds like an IAC control problem. Check the wiring at the back of the IAC connector. I’ve seen failures there with the wire corroded through.

 

[jonheld]

Sounds like an IAC control problem. Check the wiring at the back of the IAC connector. I’ve seen failures there with the wire corroded through.

The IAC is a stepper motor. It would have to sequentially short the 4 coils to ground in the exact same pattern over and over again to get it to move. I'm not even certain that an IAC can even force the engine to rev that high. It has very little movement throughout its range.

Something else is going on here that I can't understand. How could any gas engine rev that high without the throttle plate moving?
If the ECU was dumping fuel through the injectors, there's not enough air coming in and she would flood out.
If the TPS was faulty it would throw a code. The TPS doesn't control anything. It just feeds info to the ECU. If the ECU was getting a faulty reading it would start to dump fuel thinking that it was off idle. But the throttle plate still wouldn't move.

I don't understand how this could possibly happen. Please help me.

 

[ace10]

How about posting a video?

 

[Fj80oregon]

this guys trolling, no way it’s reving and not dying without the throttle plate moving it would restrict the air flow and die.

 

[earlsquirelson]

this guys trolling, no way it’s reving and not dying without the throttle plate moving it would restrict the air flow and die.

Will try to post video. I forgot to add 1fz-fe with auto gas added. This issue occurs on both gas and petrol.

 

[earlsquirelson]

SUA video
Please note: the taco not working is a new thing only just happened this morning but you should be able to hear that it hits about 5 or 6k almost straight after ignition before I turn it off

 

[earlsquirelson]

The IAC is a stepper motor. It would have to sequentially short the 4 coils to ground in the exact same pattern over and over again to get it to move. I'm not even certain that an IAC can even force the engine to rev that high. It has very little movement throughout its range.

Something else is going on here that I can't understand. How could any gas engine rev that high without the throttle plate moving?
If the ECU was dumping fuel through the injectors, there's not enough air coming in and she would flood out.
If the TPS was faulty it would throw a code. The TPS doesn't control anything. It just feeds info to the ECU. If the ECU was getting a faulty reading it would start to dump fuel thinking that it was off idle. But the throttle plate still wouldn't move.

I don't understand how this could possibly happen. Please help me.

I have no idea either, it has to be getting air and fuel… note the issue occurred with IAC valve on and off the throttle body.