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Discussion Starter #1
Hey guys,
I have and '89, XL, 5.0 (Speed density), AOD that has 180,000 miles. When I first start the bronc the rpm's spike to 2000, then settle down to 1000 or so. When you put it in gear the rpm sinks to 800ish and stay there. When slowing down from speed to a stop the engine drives the tranny thru the gears then settles at 700-800ish at a stop. In traffic the engine will surge unexpectantley and i have to mash the brake to keep it still. When put into park after driving the rpm spikes back to 1000 and then settles down to 600ish were it should be.

I've spent around $50 in carb and brake cleaner on the looking for upper intake leaks, all over the vacum lines including in the cab for the vent system. Ive changed the IAC and the TPS. Cleaned the TB. No codes.

I am at a loss and I am about to sell this pile if I can get it fixed.

Please help.:banghead :banghead :whiteflag :whiteflag :banghead
 

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Not sure a vacuum gauge will work. Once the motor changes its idle speed the vacuum reading will change anyways. But then again I never tried using a vacuum gauge so i could be completely wrong.
 

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Practicing Infidel
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2FFords said:
Hey guys,
I have and '89, XL, 5.0 (Speed density), AOD that has 180,000 miles. When I first start the bronc the rpm's spike to 2000, then settle down to 1000 or so. When you put it in gear the rpm sinks to 800ish and stay there. When slowing down from speed to a stop the engine drives the tranny thru the gears then settles at 700-800ish at a stop. In traffic the engine will surge unexpectantley and i have to mash the brake to keep it still. When put into park after driving the rpm spikes back to 1000 and then settles down to 600ish were it should be.

I've spent around $50 in carb and brake cleaner on the looking for upper intake leaks, all over the vacum lines including in the cab for the vent system. Ive changed the IAC and the TPS. Cleaned the TB. No codes.

I am at a loss and I am about to sell this pile if I can get it fixed.

Please help.:banghead :banghead :whiteflag :whiteflag :banghead

Spray flamable starting fluid

around all the gasket mating areas and listen for an rpm increase(with it running). No increase ? Change the CTS (coolant temperature sensor) $19.00.

Sixlitre
 

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Discussion Starter #7
Thanks for the advise Sixlitre. I'll try Ether this weekend. I am baffled, I really didnt do anything to it last night when I took the dash apart but now it runs fine after I did the self test. I think you may be on to something with the sensor, as intermitent as this problem is.
Anyways thanks again.
 

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Back in TEXAS
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1,967 Posts
When mine was doing this it was the TPS and MAP sensors. According to Ford (I didn't know how to pull codes then) both sensors were bad.
 

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Leaks

At the ford dealer we use propane to find vacuum leaks your engine will run rougher near a leak try also checking your brake booster your check valve might be forcing pressure back into your intake
 
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