I have a 2004 Ranger 3.0L, Iv owned it for a little over 2 years....

The Truck has had engine trouble since it hit 80k. I have had both facotry heads fixed (not replaced) because of low compression. I have changed the Fuel Filter, Plugs, Wires, and Coil Pack.


The engine runs rough when its cold and on fast idle. I can drive the truck for a while stop somewhere and it will idle smooth no shaking at all. The next time I stop it will act like it is going to die. Other times when I stop it will be running smooth and start shaking if im sitting at a red light long enough, I can watch the Tach moving up and down. I have never had the check engine light come on, the truck is driven daily ~80 miles a day to school and back home. I have also cleaned the throttle body and MAF. The Idle control valve appears to be working properly, I can unplug the wires while it is already idling rough, and it only make the engine shake worse.

I am completly lost as to what the problem is. I can change the plugs and the truck will idle smooth for about 2 days and the problem will return. The only other thing that i can note is that a mechanic told me that the engine was not running hot enough because you can hold the top radiator hose in your hand with out burning your hand after the engine is fully heated.

Any advice is appreciated

 

you seem to have covered a good list of possible culprits...

Check for vacuum leaks. Excess air that is unaccounted for can cause abnormally high cold revs and stuttering/stalling.

make sure all plugs are tight so its not a major loss of compression to blame

and is your coolant rusty at all? could be a clog in the radiator or in one of the line or your thermostat is stuck shut and not allowing for proper cooling. all good things, and easy things, to check

 

The coolant is good and clean, when I had the heads fixed i drained the radiator. I figured it was close enough to a 100k to do it. The plugs are tight, its on third set since i bought it. I have been all over the engine looking for vacuume leaks and havent been able to find any. I have ran my hand over the lines trying to feel for leaks with no luck. Even when its acting up the motor is good and quite. Everything under the hood appears to be in excellent condition (on the outside.) What ever is causing the problem is something the computer cannot find. I can have days that it will run smooth all day and the next it will run like crap.