1996 Mercury Villager with idle problems

I have a 1996 Villager, with 86,000 and it has developed a severe idle
problem. You have to keep the gas to it until it warms up and then it
improves enough so you don't have to hold the gas pedal when stopped
at a light. I took it to a mechanic, who charged me $80 for a
diagnostic check and told me he couldn't tell me what the problem was.
Now the merc dealer wants to charge me $150 to run the same test. But
they said they guarantee they would find the problem. I'm getting
really sick of all these rip-me-off mechanics.

Does anyone know any good websites where I can try to troubleshoot
this myself. I've changed out the fuel filter, air filter, plugs and
wires with no improvement. I change gas, ran some good fuel injector
cleaner through it also.

Any help would be appreciated.

Thanks,

Peter
Did you ever have any luck. My 99 Villager has problems running rough at idle and driving AFTER it warms up. We have fought with this for a while now and have also replaced the plugs, wires, dist cap and added fuel injector cleaner. I just can't seem to isolate it. The only codes we have been able to pull is for a miss on Cylinder 4 and knock sensor. Most of the things I have read is the knock sensor is probably caused by the misfire of 4. I am just curious if the knock sensor fixed it for you/ Thanks.