The truck starts fine, idles fine, and will even roll forward or backward in Drive or Reverse, but the moment you go to give it gas, the engine begins to run real rough. It acts like it's missing or misfiring, but when you get to about 40mph and push the throttle down all the way, it takes off and runs just like it used to. I've put in 93 octane gas, fuel system cleaner, changed the air filter, changed the oil + filter, Fuel Filter. Checked the spark plugs, wires, distributor cap and rotor button. I'd like to get this fixed and keep my tuck running, I'm just unsure of what the problem is, any help would be greatly appreciated! Thanks!

Also just found out how to pull codes... I drove it this morning about 27 miles with the problem about 4 hours ago, checked the codes and it put out a 12, a 17, then the 55

12 Direct battery input to PCM was disconnected within the last 50 key-on cycles (normal)

17 Closed loop temp not reached or engine cold too long <--- Huh?

 

I would suspect the coolant temperature sensor/wiring or the throttle position sensor. Both can be tested before you decide to replace anything.

 

well went ahead and replaced the temperature sensor. It was VERY old... maybe even the original or close to it. It has a -little- bit better time, but I'm still kinda at my wit's end. Going to check the throttle position sensor and the wiring as best I can today

Can't seem to find anything on the Throttle position sensor in my haynes guide, and the wiring to the Temp Sensor seemed fine. What do you recommend I do about the Throttle position sensor SEAL? I've never tackled that on this truck before, I'd appreciate any advice or tips you might be able to offer me.

 

TPS and Wiring are perfectly fine. Did find out that there's a little bit of an issue with the injectors. Replaced the thermostat because it was getting pretty old as well, and then noticed that the injectors were spitting and sputtering. After letting it run in park for 20 mins, it smoothed out and runs perfectly fine.

I'm wondering why the injectors on the TBI work fine after the motor warms up for 20 or so minutes without driving. If I drive it, it seems that the cooling system cools the motor back down, and the problem starts again. I'm probably just going to replace the injectors, but for now it seems 20 mins before driving it is the magic trick.

 

Does the truck have a thermostat, or perhaps a stuck open thermostat?

 

As throttle body injectors get gummed up they tend to stick and the spray pattern becomes undependable. As the injector warms up the gum becomes softer and may help the pattern. This problem will get worse if not dealt with as the gum starts to harden. I would run a bottle of Seafoam through it by adding it to a full tank of fuel. If that doesn't fix it replacement of the injectors would be called for. IMHO

The TPS should be covered in Haynes in the emissions and engine control section.

If the engine warms up and cools down while driving the thermostat is not working correctly or not there.

 

Or the wrong temp thermostat.

 

Even the wrong temp thermostat should allow the engine to warm to its designed temp and hold it there if it is working correctly. It should not fluctuate noticeably.

 

@150 - Thermostat has been replaced, took it out and it was FUBAR, so I picked another one up.

I think I didn't do a good job explaining it, but when the truck is parked running, there isn't a lot of air hitting the cooling system like there is when it's driving. It just takes a little longer to warm up and smooth out if I drive it before it's warmed up, not that the temp is all over the place.

@Seal - I was thinking the same thing, I noticed that was what you suggested for another person as well. With my luck they won't be cleanable, and I'll have to replace 'em. Just glad that's all it is. Thanks for the help guys