I have a 89 F150 351w, just put a newer computer in.

When I go to my truck in the morning it starts fine, but only idles at 800rpm. (idles at 600 rpm when warm). Also ever time after the first start, if it sits for 30-40 min, when I go back to start it, It has to spin and spin, then I have to give it some gas for it to start.

Has my Air temp sensor, or water temp sensor gone bad?

 

I would susppect the ect is bad. You can check it with a ohm meter at different temps.

 

Whats a ect? Sorry don't know all the abbreviations.

 

Its the coolant sensor the computer uses to read engine temp. It's on the front of the engine by the thermostat housing

 

ok, yeah I know what your talking about, I've replaced it before

 

There is also a temp sensor for air temp on the top drivers side of the intake. I was having cold temp start problems with my old truck a while back and changing out both sensors cured it. One or the other was bad. These sensors are basically the choke so to speak on a efi engine. Cold=more fuel,hot =less fuel.

 

I will probably replace both, cuz its like its not giving it enough fuel cold or hot. When its cold it starts great but doesn't have very much fast idle (800 rpm). When its warm, its hard to start.