Ford Repair: 91 grand marquis.... stalling, grand marquis, coil pack

Question
I understand you are a "Ford" expert, but there is no expert listed for Mercury... please help....  I have a 91 grand marquis. about 2 weeks ago, the check engine light came on and it started stalling. In order for it not to stall at a stop light I have to keep one foot on the brake and the other on the gas. Driving down the road the check engine light goes out and the car runs like a champ. Last week I took it to have it checked as to why the check engine light was coming on. They couldn't pull and codes from it. I left there, and went about 1/2 mile down the road and it stalled and would not start back up. Got a tow to my boy friends home, (he works on cars). Three days later the car started, but the same thing, would not idle. We checked the fuel pressure, fine, replaced the fuel filter, tested the coil pack, tested good, tested the ignition control module it tested fine. changed the distributor cap and rotor. Any other suggestions? Please....

Answer
keep in mind, this is a little out of my time frame but, have someone disconnect the line to the egr valve, it's possible it's sticking open causing this concern. if this doesn't fix it, replace the idle air control valave.. keep me posted. take care and be good... -b-