I have a 1991 f-150 with the 6 cylinder 300 manual trans. The problem started all of a sudden with my truck stalling and running a little rough about 3 weeks ago and kept getting worse until now. Now at start up with no pedal it won't start, like it's not getting any fuel. If I tap the pedal it starts and stalls , and this goes on for about 5 minutes. After that if I tap the pedal like a million miles an hour I can get it to stay running but rough. When I pull out it wants to stall , it feels like it has no power but it seems to me that if I get it to the top of the rpm range for the gear I'm in it starts to pick up. If I put the pedal to the floor it picks up with no loss of power and seems to run normal for accelarating, but if I try to keep a constant speed it bucks and surges like a madman. If I pull to a stop I have to pump the pedal like crazy or it will stall.
I noticed a vacuum line broke that went from my intake to a spliter that goes to my heater(it hasn't worked for 6 month). I replaced the line and my heater works ,truck runs like s@*T, if I take the line off it still runs like junk but slightly better.
I replaced the air filter, breather filter, cap, rotor,fuel filter. I haven't replaced the pcv valve because the one that they gave me at the auto parts is a different size hookup than the hose from my air box. Also the pcv in my truck now keep blowing out of the valve cover and if you shake it you can't hear it rattle so I think it's bad.
I changed the EGR and the throttle postion sensor, but no luck.
I'm thinking it is a sensor of some sort because like i said at full throttle it's ok,and from what I understand at full throttle all the emmision sensors usually are at 100%(wide open) since at that throttle postion there is no care for emmisions.
If anyone knows of a possible cure let me knoe because I don't want to just start changing random sensors, I'd rather know what sensor it is and why, or if it's not a sensor what it is.
THANKS IN ADVANCE for any and all help!!!!!!

 

I've been having similar issues but got the bad idle and surging taken care of. Did you change or clean the iac and also my manual says you must adjust the tps after changing it (except on the 4.9) and did you also reset the computer after changing it? I was told if you didnt it wouldnt change a thing even if it were bad good luck and keep us updated....

Daniel

 

i'm going to clean and check the iac. What should i use to clean it? Carb cleaner or something like brake cleaner?
I don't see how to adjust the tps. There is nothing on it to adjust. I do have a 4.9.
How should I reset the computer? Just unhook the battery for a while or what?
I forgot to put in my post that i did check the codes KOEO(key on engine off) and the codes I got where:
122- TP sensor circuit below minimum voltage
126- BP or MAP sensor higher or lower than expected
171- Fuel system at adaptive limit, HEGO unable to switch
172- HEGO shows system always lean
181- Fuel at rich adaptive limit at part throttle;system lean
332- Insufficient EGR flow detected
556- Fuel pump primary circit failure

I changed the EGR because of the 332 code, and I changed the tps because of the 122 code. I haven't checked the codes again, but i will and i'm also going to clean the iac and clear the computer tommorrow. hopefully that's it , we will see. THANKS for the reply!

 

PKRWUD once said to unplug negative battery cable and pull head light switch for a bit to drain all the circuits as a way to reset the computer and i personally bank on whatever he says. As i said the haynes maunal says you dont have to adjust the TPS on a 4.9 but as far as cleaning the IAC i used carb cleaner to clean mine and it did fine so if it were me id just pick up a can hope that helps give me a hollar and let me know how it works out