idle question

[keith300]

have a 1991 ranger 2.3 5spd with a/c. the truck idles at 500 to 600 rpms when warmed up was wondering if this was a little low. with A/C on no change in idle. all the other rangers iv had idled around 1000rpms but those were the 4.0 motor so i don't know if that makes a difference.
the reason i bring this up when taking of it has a knocking sound and puffs a little blue smoke out of the exhaust. if i give give it a little gas around 1k rpm and slip the clutch a little it takes off fine. any advice will help thanks o and the truck gets around 19 mpg which seems low

newly replaced items
fuel filter
spark plugs
air filter
cleaned MAF
sea foamed

 

[Sprag-O]

Should be around 800rpm and higher I imagine.

Not sure on the 91, but I imagine its the same as the 95+ with OBDII, the ECU controls idle, not the idle set screw.

May want to look into replacing the IAC and the TPS on the truck, they make a big difference at idle.