94 t'bird runs/idles rough

Hi y'all,
I have a '94 T'bird that runs rough. It is the LX model with the 4.6l V8 and has about 180k miles on it.
One day i filled up the tank and my car started running really bad.
Leaving a cloud of smoke behind and getting about 3/4 mpg. I added some Heet to it and it did not help.
I took it to a garage and they recommended replacing the EGR valve, EGR position sensor, 4 oxygen sensors, spark plugs/wires, cleaning the injectors and the fuel filter. After they did that, it still ran bad.
They replaced the mass airflow sensor and that did not help. Next they replaced the computer and it got better.
It runs now, but still misses a little. It seems to be getting much better mileage- maybe 18-20 mpg, which is about as good as it has gotten for a while. The roughness if very noticeable at low rpms (less than 1k) or if I hit it hard, and is less noticeable at higher rpms.
The garage says that all cylinders check good on compression and that all injectors are matched and that the timing is right on the injectors.
The garage recommended driving it for a week and seeing if the computer 'learned the car and all the new sensors'.
I have been driving it for about three days and it is not getting any better.
Any ideas?
TIA,
Mike W.
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did the garage just throw parts at it or did they check for error codes first ?
things left...
fuel pump, fuel filter coil packs, camshaft position sensors, slop in the timing chains, bad wiring harness, bad connections, cracked vacuum hoses. Have you ever poked around www.tccoa.com ? If they are still around there used to be alot of good info on MN12 T-Birds there.
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Ouija board
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This is Helter-Skelter diagnostic work ...

Did they replace the IAC (Idle Air Control)?
You can likely get error codes gratis from certain auto parts dealers (i.e. Autozone). The OBDII connector is under the dash, shotgun side. Report any codes here and someone may be able to further help.
I'd pull a couple plugs just to see what they looked like.
Puddin'
"Well, there's two trains runnin'. Ain't neither one goin' my way. One run at midnight, the other run just before day." - from "Still A Fool", Muddy Waters, maybe 1949
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