my 91 f150 4.9 has some running issues and i am at my wits chasing the problem down.. every time I start it after the truck sits for a period of time .whether it sits all night or just sits for 10mins , it will start every time but will idle at or above 1500 rpms then idle down to below 500-600 rpms and die. its got a lopey sputtering idle . it will do this every time untill I hold the throttle down and hold it above 1500 rpms untill it will hold a smooth idle and stay running....here is what I have done ..all parts are new and hasn't been on truck maybe about a month..new front tank fuel pump(front tank is the one I use). new fuel regulator, new fuel filter, new motorcraft plugs, new motor craft wires, new IAC, new TPS, new cap and rotor, new o2 sensor, new egr sensor,various new vacuum lines.timing is set at 14deg btdc..plugs are gaped at 45-46. . like I said the engine will start every time but it will sputter till it dies unless I hold the throttle to warm it up for about 5 mins or so before it will hold a smooth idle of about 1000 rpms..sorry for the long read but I don't know what to do to fix this truck..thanks for any advice and help..

 

Did you adjust the TPS to spec or just throw it on ?
Also do a fuel pressure test to see if anything weird is happening there. I know you have new parts, but that doesn't mean you have proper fuel pressure.

 

my 95 had that issue and it turned out to be the iat[intake air temp] sensor,took mine out and cleaned it with alcohol and it got better,replaced it and then it went away,its located on front of engine on intake..hope this helps

 

fuel pressure is at about 52 psi with koeo and fuel regulator with vacuum off and koer is about 60 or so psi..i just bolted on the TPS, I wasn't aware there was a adjustment. If there is a adjustment then please show me how cause I don't know...lol

 

I have looked and I don't see the intake air temp sensor you speak of..does a 91 4.9 have this sensor...

 

91 won't have air intake sensor. Sounds like a bad coolant temp sensor located on thermostat housing.

 

Back on feb 22 I posted "testing the tps". That has the info. Then you loosen those 2 screws and turn it till it reads exactly right at closed throttle. Adjusting it is a "must do" at installation.
sdmartin might be right about the temp sensor too, but I don't know how to test that one, but I don't think they're real expensive.

 

my 91 has the intake air sensor.. I just bought it at advance..i also bought the coolant temp sensor..

 

you might want to send me that link to that thread so I can read about testing and adjusting

 

Yeah, I don't know how to do a link to it. But if you click on my name and then on threads, I'm pretty sure it was feb 22.