Greetings everyone!

I just picked up an 89 F-150 Ext Cab, with the long box and the 351W V8. It's a rusty old beast, with a claimed mileage of 115k. Not bad for $500.

I took it for an oil change and bought the standard plugs/wires/cap/rotor/air filter for it with plans on replacing all of the above. That is, until I looked closely under the hood. I think I'll wait on the plugs for a different day. I did find one plug wire off which solved my steady misfire.

My more important question is this: when starting it cold, it seems fine for a very short time, then the idle drops quickly (within 20 seconds or so) and then it barely stays running (like an old carburator with choke problems), almost needing to have a light foot on the accelerator. Once it is warmed up, all is fine. A similar situation occurs on warm start too. Having Merkur Scorpios in the past, I have had issues with the Engine Coolant Temp sensor giving fits and having a similar problem with starting. Does this truck have one and would this be a likely culprit? No, I don't have a shop manual for it yet but it is on order. If you all think the ECT might be it, I'll pick one up tomorrow and try it. One thing I did do to it today was clean out the TPS so that worked freely. No effect on my other problem though.

Any input is appreciated guys. I am sure I'll have more questions as I spend more time with Pig.

Eric

 

By TPS, do you mean the idle-air bypass?

I would first suggest to get the computer codes read first - may help give better direction. AutoZone reportedly reads these for free. I hates going on a trial-and-error, divide-and-conquer replacement voyage, except as a last resort.

There is a coolant sensor - be sure to get the right one - IIRC, there is one for the instrument panel gauge, and another for the computer.

 

On the Scorps, the Throttle Position Sensor was right on the main throttle body. It had 2 holes inside it with some spring-loaded rod that went up to an electronic sensor. It would get gummed up with the same crap that was on the engine side of the butterflies. I found it on the truck and did the regular cleaning of that. It always seemed to help the Scorp run better especially at idle. The ECT was right on the manifold and was supposed to send the coolant temp to the computer so it could make the proper adjustments to fuel settings, etc.

I am pretty sure the part I am talking about above is the TPS. If I am wrong, I will stand corrected. Perhaps I may have to take a pic of it and post it. I can go to Autozone and have them pull codes tomorrow too. Why didn't I think of that??

 

From your description, I would almost bet real money that you cleaned the idle-air solenoid - which is a good thing - these do gum up.

The TPS is on the bottom of the main butterfly valve rod - cleverly placed underneath to heighten the degree of difficulty to access - it's plastic with three wires coming out.