Engine sputters under load. engine surges then drags---sometimes it runs normally then for no reason problems arises again.

Sounds like you have a fuel system problem

I guess I should start with the obvious - the engine is under extra load with the ac running. So any minor problem with the ignition or fuel system will be magnified.
Could be weak spark plugs or wires, anything that would cause a miss.
There could be a problem with the amount of drag coming from the ac compressor too.

chek plug cables first of all

Sometimes the computer will have an intermittant glitch. Wait to see if problem reoccurs and monitor it based on engine start-up/run conditions. ( I. E.) Hot, Cold, Under A Load, Idling, Cruising.

Does it use spark plug wires or individual ignition coils for the each plug?. My 98 intrepid uses coils and occasionally I have to change them out cause it would start to miss when normal temperature was achieved. If it uses wires, try replacing them, along with the spark plugs.

Once you get your Ford to start, does the engine run normally ? If yes, then timing not an issue. If no, you may consider timing, but not until other components have been checked.
Have you done any maintenance to your vehicle like a tune up, air filter / fuel filter change. Have you checked fuel pressure ?
Have you checked for any codes in the engine control module ?

try replacing the throttle position sensor

Ok there are several options such as water in the fuel or dirty fuel for starters. Another option would be clogged fuel injectors or a dirty map sensor. Check the spark plug wires to be sure that they are on tight and none are worn at contact points such as rubbing against a sharp edge. Let us know what the code(s) say.

I have the same problem on my 95 grand cherokee laredo. Sometimes it starts out fine and after about 10 miles it starts spitting and sputtering. Then after a while it seems to clean out and run fine again for a little while. Then other times it starts out spitting and sputtering at the begining. I changed the fuel filter and that was not it. It is a 4.0L 6cyc. Any Ideas?

Thanks,
Broken Arrow, OK

Had the same problem with 1999 Quest - turns out that the distributor was going until it finally died. It stuttered andf kept shutting off when driven about 20 miles or so. Would start normally when cooled and off again when hot. But yours could be a different problem; not sure.