If its a fuel injected motor idle is handled by the computer. There usually is a "base idle speed" around 800-1000 RPM. This normally doesn't need to be adjusted.
Have a look for carbon build up on the butterfly as well, this will influence idle too.
If the engine is revving high and low while it is idling, then that can be the idle air valve (what was told to me by a professional). I don't know if it can fix itself because I had mine hibernating for about a year and it stopped.
The low side ac port for the 1990 e 150 should be on an aluminum pipe. The pipe is on the passenger side of the engine compartment just beside of the battery.
Because the efficiency of the fan and the water pump degrades at low RPM.
No, it wouldn't affect the idle unless you were somehow overheating the engine.
have someone check the icm (idle control motor)
Idling too low or a bad lock-up torque converter solenoid.
The #1 cause of cold air from the heater when the car is stopped, or the engine is idling, low engine coolant levels.
Chances are, particularly if this is an automatic transmission, you are low on tranny fluid. To check this, the engine needs to be at normal operating temperature and idling. Checking tranny fluid when the engine is cold and not idling will give a false reading, indicating that it is full ...
Perhaps the A/C is drawing too much power from the engine, could be the engine is idling too low.
sitting and idling ?possible bad engine or trans mounthave them inspected
Sonds like the idling speed is too low - it can be adjusted (Usually with just a screw driver) if you know the right screw to turn to give the engine higher idling revs.
The low pressure port on a 1990 Ford van is in the rear of the engine compartment. It is on the passenger side, near the firewall.