Carbon canister problems can cause idle problems because of a possible vacuum leak. The vacuum source to the canister valve is at the front lower side of the upper manifold. The hose may be leaking, or the cap (if someone capped it) may be leaking. I have see instances where the tube was loose in the upper manifold & needed some epoxy to seal it up tight.
Test proceedure is to carefully inspect the tubing and hoses for cracks and damage. if you don't find any and the canister plumbing is intact, temporarily disconnect the feed line from the upper manifold and cap it off. If the car idles better, you have found the source of the vacuum leak.
I would not advise simply disconnecting the canister valve & associated plumbing. It provides fuel to the engine at cruse and vents the gas tank. Disconnecting it will make the car smell like gas on a hot day and stink up your garage - possible fire hazard if you have a gas water heater. Not to mention that you can't pass emissions or probably can't sell the car in a state that has emissions laws.
Air Injection problems are smog pump problems. Codes 44 & 94 are most common because people rip out the smog pump vacuum lines & control valves. Here's the test path for codes 44 & 94...
Codes 94 & 44 - AIR system inoperative - Air Injection
Check vacuum lines for leaks, & cracks. Disconnect the big hose from smog pump: with the engine running you should feel air output. Reconnect the smog pump hose & apply vacuum to the first vacuum controlled valve: Its purpose is to either dump the pump's output to the atmosphere or pass it to the next valve. The next vacuum controlled valve directs the air to either the cylinder heads when the engine is cold or to the catalytic converter when the engine is warm. Disconnect the big hoses from the back side of the vacuum controlled valve and start the engine. Apply vacuum to the valve and see if the airflow changes from one hose to the next.
The two electrical controlled vacuum valves mounted on the rear of the passenger side wheelwell turn the vacuum on & off under computer control. Check to see that both valves have +12 volts on the red wire. Then ground the white/red wire and the first solenoid should open and pass vacuum. Do the same thing to the light green/black wire on the second solenoid and it should open and pass vacuum.
Remember that the computer does not source any power to actuators, relays or injectors, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif
http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif
