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Discussion Starter #1
I've got an '88 with the 5.0 and automatic. It just did this two days ago, and I haven't driven it since. The engine stays revved at about 2,000 rpm. Even at full running temp.
The throttle contol (on top of the throttle body) returns all the way to the stop.
Unclipping the cable to the transmission from the throttle body has no effect.
The fuel pump in the tank was replaced in August.

It doesn't appear to be a mechanical problem (stuck cable, etc) What sort of things should I be testing? Any and all help is GREATLY appreciated.
 

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In Front of Jopes
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Is the floormat stuck on the accelerator? I have Husky mats and it got caught on the acceleration causing what you described.
 

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Discussion Starter #3
Nope, pulled the floor mats out......
When put in gear it pulls forward, ALOT. The tires spin at stop signs, and forget about cornering. The icey roads are going to kill me and the Bronco. In park it revs to about 2,000, and in gear about 1,300 rpms (with the brake firmly applied)
 

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Discussion Starter #5
I haven't had a chance to really get into her.... but am looking for direction. I got as far as looking at the cables and linkage on top of the throttle body. I get home after dark every day. Tomorow is my only whole day to work on it.

I'm secretly hoping its something simple, as it just popped up outta nowhere.
 

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Check for vacuum leaks as mentioned.

If you unplug your IAC, what happens?
 

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had the same problem on my 87 my tps was stuck go down to the bottom of the throttle body and unplug that clip and see what happens and if not do what broncoforlife said, if still happenening i guess check for vaccum leaks ...good luck
'
 

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Discussion Starter #8
Thanks for the replies.
Now I'm really stumped. I checked the resistance at the IAC and it is correct at 10.3 ohms (should be between 7 and 13). But the voltage is at .3 instead of the 10.5.

On the TPS I get resistance readings from the signal return and VREF terminals but not the return and tp signal terminals. I get voltage readings from the signal return and tp signal terminals though (4.95 volts) but no change as throttle position is changed. I am assuming the terminals are mismarked in my HAYNES repair book.

The idol this morning has kicked itself down, and is running normally (with a bit of a sputter and up and down idle while it is cold)
 

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Discussion Starter #10
Thanks for the graph. Good info.

Can anyone give me the propper wire/ plug diagram? The TPS has 3 wires. one under the ^ is the signal return. clockwise to the right is the TP signal. The one conterclockwise to the left is the VREF, according to the HAYNES book. (looking into the unplugged plug). The VREF SHOULD be showing a 5 volt with the key on (showing signal from the PCM). The return signal (black probe on the voltmeter) and TP signal (Red probe) should show voltage of .1 up to 5 volts when the throttle is turned.

When I plug the voltmeter in to the return, and tp signal terminals, with the car on not running, I get 4.95 volts at closed throttle and no change with opening the throttle.
 

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Discussion Starter #11
Thanks again Steve83. The sites have confirmed what I thought..... my wires are mismarked in the book... So my TPS is not showing any change in voltage with the throttle being opened, but it does show resistance when unplugged.

Does that make it the culprit? I show no voltage when inserting the probes into the back of the plug. (return and tp wires). Or should I be more concerned with the wires themselves not making a connection?
 

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TPS output voltage at idle should be ~.95v, just as long as it's under 1.0v, and at wide open can be anything from around 4.5-5.0v.
 

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Satyr of the Midwest
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Just an FYI: in later ROMs, they made it so that it really doesn't matter how close it is to 1.00V at closed throttle. The PCM just reads the TP voltage at start, monitors it, and updates it if necessary with a new minimum. :thumbup Ford slowly got smarter over the years, although it seems it took them until about 1992-3 to figure this little gem out.
 

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Way to rain on the .95v parade. :duh

:toothless


I remember reading that it was a big thing in the mustang crowd, that it really effected off the line response. What was it about the older EEC's that made it funny if you weren't right at .95v at closed throttle?
 

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i had this problem in my mustang, check the gaskets on the intake, an air leak will cause this.
 

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Satyr of the Midwest
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I remember reading that it was a big thing in the mustang crowd, that it really effected off the line response. What was it about the older EEC's that made it funny if you weren't right at .95v at closed throttle?
Yeah, on the older PCMs, like Mustang A9Ls and A9Ps (and all previous speed-density PCMs) a closed-throttle TP voltage above one volt will cause trippy driveability problems, particularly low-speed surging. With these later ones on these rigs though, it seems they've done away with that border. I've set mine from 0.75V to 1.15V +/- DVOM error, and have noticed no change with either my old or new PCMs (A2Z3? and BIO0). :shrug
 
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