I recently bought a 91 formula 350. The car idles fine when first started up but the more it warms up the more messed up it idles. When the temp get to about 200 the whole car shakes and it feels not all cylinders are firing. However once the car is moving off idle it seems to run fine. So far I have replaced the distributor cap and spark plugs. I also replaced a couple vacuum hoses but cant find any more leaks. Any ideas what to check next? I am waiting on a ALDL adapter cable for my scanner so I can check fuel trim and timing.

TPS Throttle position Sensor. Set @ .54Volt. Had the same problem, that was the issue for my car.

Sounds like a classic case of bad fuel injectors. Get an ohm meter and check the resistance of the injectors (unplug the connector and probe the terminals of the injector). It should be around 16ohms when cold and more than 12 ohms when hot. If any are less than 12 ohms, its a bad one.

Well i checked the TPS sensor and it was a little high. The lowest i could get it to go was .63 volts. I have not check the injectors yet. I got my ALDL cable today and I was checking out the data. I have no DTC's, the Block learn was at 120, Integrator was around 128 spark advance at idle was 16-17 degrees. IAC counts were about 20. The o2 sensor seems like its working. It was swinging lean to rich in closed loop with lots of cross counts. So it doesnt seem to be running extremely lean or rich.

I did notice one strange thing. It said my oil temp was -39 degrees. Do our cars have oil temp sensors? Could this be part of the problem?

No oil temp sensor.
Do as Kevin said and check your injectors.

i agree.. multec= headache
those injectors if ohm out less than 10ohms they are shot. 12 is borderline shot. Get the Bosch replacements from FIC you will be happy but make sure its the injectors first. Don't throw parts at it.

Ok I checked the resistance on the injectors

Passenger side from front to back
8.6
5.7
15.9
15.8
Drivers side front to back
16.7
11.1
15.5
12.9

YOU HAVE 3 BAD INJECTORS GO TO WWW.FUELINJECTORCONNECTION.COM
AND ORDER A SET OF THE BOSCH 3'S THEY FIT WITH NO MODS.
HAVE FUN