1989 bronco rpm problem

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ft - 15 Oct 2008 06:22 GMT

Hi everybody, i have a problem with my 89 fullsize bronco. It has a
302 and a 5 speed. The problem is when at idel the rpms will all the
sudden jump up to about 2000 rpm, and stay there for 3-5 seconds and
then drop right off to 400-500rpm and sometimes quitting commpletly.
Its like it wants to go in to cold idel even when its warm and like i
said the rpms will drop right off. I havent tried any fixes yet, just
wondering were i should start.

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lugnut - 15 Oct 2008 14:23 GMT

>Hi everybody, i have a problem with my 89 fullsize bronco. It has a
>302 and a 5 speed. The problem is when at idel the rpms will all the
[quoted text clipped - 3 lines]
>said the rpms will drop right off. I havent tried any fixes yet, just
>wondering were i should start.

Sounds like either an IAC (idle air control) or TPS (throttle position sensor).
I have seen the TPS cause this without setting a fault code. You should have it
scanned for fault codes. They can usually be extracted as a free service by
many parts stores. If you post the codes along with the description from the
scanner, someone here can probably help you figure it out. If I had to take one
shot at it with no further info, I would replace the tps which is fairly cheap
and easy to replace with minimal tools.

Lugnut

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Jeff Strickland - 15 Oct 2008 18:56 GMT

>>Hi everybody, i have a problem with my 89 fullsize bronco. It has a
>>302 and a 5 speed. The problem is when at idel the rpms will all the
[quoted text clipped - 7 lines]
> sensor).
> I have seen the TPS cause this without setting a fault code.

I agree here.

I also agree with the suggestion to scan the codes. You can buy a scan tool
for Fords from any auto parts store, it will run about $35. It is easy to
use, and mine told me of two things that had me scratching my head wondering
what was going on. The tool saved hours of troubleshooting and a shopping
basket of wrong parts.

Lugnut says the parts store will pull codes for free, but that is typically
limited to OBD II codes, your truck is OBD I. The scan tool for a Ford using
OBD I (On Board Diagnostics, Level One) is made by ACTRON. Forgive my error
ir there is one, but I recall the model munber as being 9515 for the
application we are talking about. (I gave my scan tool to the guy that
bought my Truck, so I have to work from memory here.)

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