Unexpected wide open throttle

3640 Views 14 Replies 8 Participants Last post by B10alia, Oct 7, 2012

BillW

Discussion Starter · Oct 2, 2012

I started a thread about my speedo not working and I haven't had the time to really work on it but now a new problem has reared it's ugly head. Lately, not all the time, when I start my 1991 Caravan 3.3 2wd the throttle seems sticky. In fact about four times now when I start to drive the throttle goes to wide open. It goes wide open even when I have hardly touched the throttle. I have lubed the cables and all moving parts, they work freely and have replaced the throttle return spring. The last time it happened I shut the engine off and pulled the throttle back and felt a heavy resistance. I started the engine and everything was back to normal and the throttle worked freely. I've nearly rear ended a couple of cars. Thank goodness that the brakes are good. I know I should get rid of it but a medical problem has made that impossible to do right now. I need to get it reliable to get back and forth to work. Any help would be greatly appreciated.

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ImperialCrown

· #2 · Oct 2, 2012

Lubrication of any throttle linkage/component is forbidden. Keeping them clean is all that is recommended.
If you have heavy resistance pulling the gas pedal back up, it would seem that the problem is at the gas pedal assembly as it is free-floating where the throttle cable is attached. Dust and hair debris in this area can cause problems as can misaligned floor mats and carpet.

KOG

· #3 · Oct 3, 2012

Replace the cable NOW!

BillW

Discussion Starter · #4 · Oct 3, 2012

It's not the cable. It moves freely. Something is pulling the throttle wide open on it's own. I barely touch the gas pedal and it goes to wide open throttle all by it's self. It's almost like the cruise control is pulling it open except it goes to wide open even if the throttle is opened by an 1/8th of an inch. I have been a mechanic on and off for forty years and I still restore classic cars and build race cars for people when health permits. The last car I built was a 68 Chevelle that ran 9.80 at 132mph on pump gas. It's just that the electrical on this Caravan is a mystery to me.

ImperialCrown

· #5 · Oct 3, 2012

Heavy coke and carbon build up in the throttle body bore and blade edges can cause a sticky throttle plate. Clean with a solvent and toothbrush/rag.
When pulling the throttle back by hand. do you mean right at the throttle body lever or at the pedal?
The IAC and TPS, even if misbehaving wouldn't move the throttle mechanically wide open.

KOG

· #6 · Oct 3, 2012

So remove the cruise control cable from the throttle body to test. I don't think that's the problem, but actually can't imagine what is.

BillW

Discussion Starter · #7 · Oct 3, 2012

ImperialCrown said:
Heavy coke and carbon build up in the throttle body bore and blade edges can cause a sticky throttle plate. Clean with a solvent and toothbrush/rag.
When pulling the throttle back by hand. do you mean right at the throttle body lever or at the pedal?
The IAC and TPS, even if misbehaving wouldn't move the throttle mechanically wide open.

Yeah I already checked the throttle body and it's as clean as can be, and it works freely. There is nothing at the gas pedal as far as I can see. Like I said, it's a though something is actually pulling the throttle back on it's own. Of course it doesn't do it all the time so it's hard to repeat the problem. I have pulled the cable to the cruise control just to be on the safe side. It's really wierd. The new return spring I put on has quite a strong pull on it and what ever it is, is pulling beyond the return spring's resistance. Another one of lifes little mysteries I guess.

KOG

· #8 · Oct 3, 2012

That's more than a little mystery. Something is BAD wrong.

peterjon1

· #9 · Oct 3, 2012

Is there any possibility of bad motor mounts?

KOG

· #10 · Oct 4, 2012

I thought about motor mounts. Those have been problems with some vehicles in the past, but the cables on the minivans have enought reach that a bad motor mount won't open the throttle. They're not 58-64 Impalas for example.

Lt. Dan

· #11 · Oct 4, 2012

I wonder if the idle control valve is malfunctioning?

Bob Lincoln

· #12 · Oct 4, 2012

The AIS cannot physically move the throttle plate or cable.

BillW

Discussion Starter · #13 · Oct 4, 2012

peterjon1 said:
Is there any possibility of bad motor mounts?

They've all been changed within the last year.

KOG said:
I thought about motor mounts. Those have been problems with some vehicles in the past, but the cables on the minivans have enought reach that a bad motor mount won't open the throttle. They're not 58-64 Impalas for example.

Even the 65 impala big blocks had that problem. The engine would lift and it would pull on the throttle and then the engine would lift more and pull on the throttle more...We were doing recalls on them still in 72. That consisted of chaining the engine down on the drivers side.

djsamuel

· #14 · Oct 5, 2012

BillW said:
I have pulled the cable to the cruise control just to be on the safe side. It's really wierd. The new return spring I put on has quite a strong pull on it and what ever it is, is pulling beyond the return spring's resistance. Another one of lifes little mysteries I guess.

Has it occurred since you pulled the cruise control cable? That is about the only thing I can think of, other than the normal throttle cable, that can actually move the throttle.

B10alia

· #15 · Oct 7, 2012

How about trying to get the car to do it in neutral while you watch the linkage? You're going to have to be ready to close the throttle manually to keep the car from over-revving with no load on it, but at least you'll get an idea of what's going on.

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