Ford: Ford F150 jumpy oil pressure needle, ford f150 xlt, air control valve

Question
QUESTION: Hi Tim.
When my truck is at idle with the transmission in drive, say at a stop sign with the air conditioner on the oil pressure needle jumps erratically near the low end. If I keep the brake on and raise the idle just slightly the needle is steady and is normal. This erratic needle situation only happens when the air conditioner is on otherwise the oil pressure is normal.  
The vehicle is a 1995 Ford F150 XLT 5 liter 302 v8 4wheel drive automatic trans.
Thanks
Chris

ANSWER: Hello,

it could be electrical or the idle is dropping too low to pump oil.  the only true way to see is a mechanical oil pressure test at idle and at 2000rpm

---------- FOLLOW-UP ----------

QUESTION: If this is a low idle problem how can I raise the idle?
Thanks
Chris

Answer
hi,

If the oil pressure is low at idle, you will have to determine if the idle speed is correct.
The speed should be about 850 rpm but is not adjustable.  If it is lower, you may need to clean the Idle air control valve and passageway and the throttle plate.

If idle is to spec and oil pressure is below 40-60psi at 2000rpm, then you have a oiling problem=  basically something broken or badly worn