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Discussion Starter #1 (Edited)
Ok I have an 89 FSB with the 5 liter motor. Every morning when I go to start the truck the check engine light comes on and the idle is low. I have to keep my foot pressed on the accelerator slightly to keep the truck from dying. Now I can drive down the street for awhile and the idle seems to hop up and the light goes out. Sometimes it will drop out for another second or two and the light comes back on but then it goes back up and the light goes off. Now while the light IS on when I have to come to a stop I have to keep my feet pressed on the brake and gas again to keep the motor from stalling. But light goes out no problem can drive it just like normal. The light seems to stay on longer when the temp is colder outside and goes out faster in warmer weather. I have taken it to have the codes read but they were old codes saved from awhile back so it seems that whatever this issue is does not register its causing the light to come on. Oh and almost forgot. It actually turns, cranks, and fires fine once the idle goes to normal it runs fine. I can drive around for awhile and say for example I need to shut it down at a few places. Every time I get back in and have to start it back up as long as the temp on the motor hasn't gone down too much the idle seems to start normal BUT it has a hard time firing the motor. To the point at a few times I thought it was going to drain the battery. And it takes more and more every time you have to restart it. Then you let it sit overnight and its back to normal as far as turning over.

I've had the battery checked and it tests good. Fuel filter changed and even ran a system cleaner through it just to be safe. Its been Seafoamed in the last year. Plugs, wires, cap, rotor all replaced. I thought maybe a leak in a vacuum leak but with the temperature thing in the mix that did not make too much sense.
 

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i had a similar problem on my 89 302, does the idle go up and down on its own?

i replaced the TPS (throttle position sensor) on the bottom of the throttle body (cheap and easy), then cleaned the EGR valve (exhaust gas recirculation) on the side of the throttle body, it was so full of carbon you couldnt see through it.

easy fix for mine, then i sold it. haha take off intake and look around for clogged lines. replace TPS and EGR valve, small stuff. try running a fuel-cleaner like barrymans b-12 or others to loosen up carbon b4 trying to clean it. try to put high quality gas / high mileage oil in the truck when you can, carbon build up is usually cause crappy gas is run through the motor.

mabye im just confusing the situation, hope i could help.
 

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Also check your IAC valve which is attached to the side of the throttle body.
 

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Pull Codes!

Diagnose the problem before you start monkeying with parts. Autozone and similar parts stores will check codes for free. Or do a search on the forum on how to read codes.

Cheers

Steve
 

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Pull Codes!

Diagnose the problem before you start monkeying with parts. Autozone and similar parts stores will check codes for free. Or do a search on the forum on how to read codes.

Cheers

Steve
Do This (Said that before).

On a side not I had the exact same problem in my Mustang. Correctly adjusted he TPS and it fixed the 6 month old problem in 6 minutes.:thumbup
 

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i had the same symptoms just yesterday. code was 122 (TPS). replaced TPS (you have to reset computer afterwards though). problem solved.
 
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