1986 Ford F-250 Will start rough, but won't hold idle.

PFOWLER

MEMBER
1986 FORD F-250
V8
4WD
MANUAL
145,000 MILES

I have to feather the throttle to start the engine, and keep feathering to keep it running. While depressing throttle the engine chokes, and upon release of throttle the engine picks up. Plugs looked fine for 20k on them, wires etc are same age. High pressure (external) pump was replaced along with filter since problem began, no results. Haven't gotten it to run without being on and off the throttle. Fuel in tank is from June '09, but I've ran rigs on much older fuel. Engine is Jasper reman'ed, installed Aug '06. Last time I drove the truck, it acted similar on start-up but much less severe. At the time it seemed to have around 40% power or so.

5 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Hi pfowler, Welcome to 2carpros and TY for the donation

Dunno if its an EFI system and a 5.0L engine if so check and test the throttle air bypass solenoid, EGR and PCV valves and the throttle position sensor-If not get back asap.

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Thursday, January 28th, 2010 AT 6:47 PM

PFOWLER

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3 POSTS

Yes, EFI 5.0L. Has that weird TBI injection setup. Rookie question, but how do you check those? Had a scanner for it, but it got dropped in my last move.

Technically it's called a TFI-IV system.

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Thursday, January 28th, 2010 AT 6:59 PM

RASMATAZ

MECHANIC
75,992 POSTS

Find the throttle air bypass solenoid/IACV and clean it out and also the EGR valve-

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Friday, January 29th, 2010 AT 11:08 AM

PFOWLER

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Ok I cleaned the IACV and EGR valve, also checked voltage and resistance. Everything seemed to be working correctly. The EGR valve spring seemed a little rough to move when I removed it, and smooth actuating when I put it back on, with no difference. I have yet to check the TPS, but I'll be replacing that if it needs to come off anyway as it's a PITA and inexpensive.

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Friday, January 29th, 2010 AT 1:01 PM

PFOWLER

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3 POSTS

I bought a new code reader today, and these are the codes it threw on KOEO;
21, Cooling Temp Sensor out of specified range
22, MAP sensor out of range
24, Air Charge Temp sensor out of range
31, either EGR valve control sensor fault, or EVAP control system out of range

On CM, it threw;
18, Loss of tach input

I'm not sure what difference it would make if I could get the engine up to operating temp before running test.