92 f150 idling problem


Old 10-28-07, 06:33 PM
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92 f150 idling problem

92 f150 5.0 302 v8 5 sp manual trans. idles at 2500-3000 rpms in netrual. it has no vacum leaks. local auto store said it's the tps sensor. i replaced it- nothing different. any info? thanks
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Old 10-28-07, 08:25 PM
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I'd almost bet you do have a vacuum leak between the upper & lower intake manifolds. not hard to check with a spray brake/carb clean around the front/sides of the two manifolds. Also look close @ you're PCV valve hose & grommet. Good Luck, Roger
Old 10-29-07, 04:57 AM
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First thing:
Pull the Codes

But yeah, I think it's a vac leak also
Did you check all the hoses?
Especially underneath those hard plastic "elbows"

* How on earth did the Auto Parts Store determine it was the TPS sensor?
Old 10-29-07, 04:10 PM
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That's a pretty excessive fast idle though. I'd be afraid to try to shift a car into gear with idling like that. Have you physically traced your linkage to see if you can actually see if there is an apparent reason, a directly related part, why throttle might be held open, rather than just rely on speculation of various sensors (TPC, IAC, EGR valve malfuncion or whatever)and hoses. My car doesn't even reach 3000 rpm at 60 mph down the highway!

Question to others: Wouldn't a bad or disconnected vacuum hose perhaps up the idle speed by say no more than 300 rpm's, from say 800 idling, give or take some? But 3-THOUSAND rpm's?
Old 10-29-07, 04:23 PM
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Originally Posted by slickshift View Post
First thing:
Pull the Codes
This is pre OBDII so pulling codes might not help....specially if there is no check engine light.

I would check the butterfly valve on the TB and see if it's stuck.
Old 10-29-07, 05:56 PM
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Originally Posted by HotinOKC View Post
This is pre OBDII so pulling codes might not help....specially if there is no check engine light.
This vintage EEC-IV computer can store many codes w/o firing off the CEL
It helps inasmuch as even if it's all clear, you can eliminate some possible problems, and it also can surprise with some information not expected to help look further

For example, there is a "TPS Sensor Out Of Spec" code...which obviously is not stored in this particular computer...

I would not try any diagnosis on this type electronically controlled engine w/o first pulling the codes-regardless of what I initially think the problem is...it's a super easy DIY job and even an "all clear" tells us something

But really I'm thinking vac leak or Air Idle Control motor
The TPS is not a bad guess, but as there are codes for it and tests to check it, it was not a good idea to simply replace it w/o further investigation

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