1994 F 150 4.9 220,000 miles and manual trans.
Runs great when cool rough when warm.
Does not over heat.
Will a malfunctioning thermostat cause it to run rough, irratic haigh idle and eventually die?
After 10 - 15 min cranks up and runs ok for a few minutes.
Then starts to kick and buck again.
Help please.

 

Probably the ignition coil.

Pull the codes from the ECM first.

 

I think you're experiencing the infamous "EGR Stumble" (lean stumble) very common with the 4.9's.
First off, I'd check the Coolant Temperature Sensor circuit (at the water pump) to verify it's functioning to specification.
If that check passes, then check the throttle body gasket to see if it's been sucked in....causing a vacuum leak. Don't forget to check other obvious known vacuum leak sources as well while you're at it.

If the TB gasket is o.k. (I'd replace it if your going to check it), and you can't locate find any vacuum leaks, try this:

Disconnect the vacuum hose at the EGR valve and drive the truck around for a while and see if the bucking and kicking goes away.
If it does, then you can do the "EGR Restictor Plate" (search this forum for a bazillion posts about it) which is a "band aid fix" or find the REAL PROBLEM which would be an unmetered vacuum leak.

I've done a version of the EGR Restrictor Plate fix, and it did fix MY stumble/ bucking problem, however I do know that I have a pretty severe vacuum leak in the throttle body where the throttle shaft is (both sides too).
A rebushing of my TB should take care of that vacuum problem.

And if you still are having the bucking/kicking problem you may want to check your computer.
Click this link:A9x ECM's (and same years ECM's) Failures Due to Age
The capacitors in my '94 were leaking and I did the described repair which cured a random missing problem I was having..........however, it did take me a couple of attempts to get the repair right.

******Note: My computer NEVER showed/stored any codes related to the leaking capacitor problem I was having******

Good Luck

Bob

 

Thanks Bob,
My engine is fuel injected.
What are you refering to when you say the "throttle body"?
And you are right. I have no codes. Just a check engine light and a headache!

 

The Throttle body is the item that houses the butterfly valves, located on top of your engine.
It has the throttle position sensor, and the idle air controler valve bolted on to it as well as the throttle linkage.........kinda' like a carburetor.

Did you disconnect the EGR line and drive it yet ?????
If so, howd' it drive ????

No codes and a check engine light.....hummmmm.......I'd remove and visually check the computer at this time just for the "peace of mind". If there is the "leaking capacitor" thing happening, the computer needs to be replaced, or at a minimum, the circuit board needs to be repaired before you can go on any further.

Keep us posted.

Bob

 

my truck runs great befor it warms up but after that ugh !!!! i have replaced the egr the egr vac selinoid the idle air control the ambiant air temp sensor the map sensor plugs, plug wires,distrubuter cap rotor cap and the fuel filter ugh i changed the o2 sensor as well , i have no vac leaks i have checked every where i cannot figure this out at an idle it runs good but when i come to a stop sign and stop it runs rough im at wits end i need help with this one

 

What year/model/engine/transmission truck do you have?

Have you ran the KOEO tests and CM display?

Is the Check Engine Light on?

 

94 f150 xlt 4x4 4.9 inline 6 cyl no codes showing

 

And no check engine light all test showing ok

 

well I have pulled the throttle body of and the plenum I have completely I have cleaned and refurbished my injectors let's see if that works update you all later

 

Crap I think I replaced everything under the Sun I clean the intake manifold replace the oxygen sensor put new egr e GR position sensor distributor cap rotor cap spark plugs egr vacuum solenoid the coil fuel filter idle air valve and map sensor I have no vacuum leaks and this thing still runs rough I'm at my wits end with this I cannot figure it out oh and I took the fuel injectors out and redid them the only thing I haven't done is put new injectors in it and a new cat any help would be appreciated

 

So you replaced a laundry list of new parts, now you have no idea if you introduced a new problem. I hope you kept the old ones. If so I highly suggest you put the old sensors back in.

Back to your previous reply in Post#9, please define "all test showing ok". Your truck should display three digit codes therefore if the KOEO tests pass you would have gotten the System Pass code of 111/111 (codes are repeated) then you would also get a System Pass code of 111/111 for the Continuous Memory display.

I also do not understand your statement about the injectors, "I took the fuel injectors out and redid them". Could you clarify what that means?

 

OK SORRY ABOUT THAT I DID THE SELF TEST I DONT HAVE ANY CODES SHOWING UP NOW AND I TOOK THE INJECTORS OUT CLEANED THEM UP PUT NEW O RINGS AND THE LITTLE CAP ON THEM THAT IS WHAT I MENT BY REDOING THEM I TESTED THEM WITH A 9 VOLT BATTERY TO MAKE SURE THEY OPEN AND CLOSED AND THEY DID I ALSO SO PUT A NEW FUEL PRESSURE REGULATOR ON AT THE SAME TIME AS I DID THE INJECTORS

 

I strongly suggest pulling your engine computer out opening it up and checking the capacitors (3 shiny blue cans) for any leaking that looks like corrosion on a battery. The computer is on the driver side lower firewall, you'll need to loosen the fenderwell to get the computer out.

Then 2 torx screws to open the computer case and inspect. I just pulled mine out and its completely shot and I had the same symptoms and exact same issues you had. I'll take some pictures of the inside of my computer for reference if I can.

 

That would be great thank you and that was my next thing to do is to replace that the computer