My chevy tracker 2003 4 cyl idle speed is less than 500 rpm but when i turned on the A/C it works fine

SOURCE: idle problem

you can't adjust the idle it's all done by the pcm.you might have a IAC going bad or sticking(idle air control solenoid)

SOURCE: With the air conditioner on

there is a white plastic knob on the vsv /firewall twist that out or in to adjust with ac on car running ?

SOURCE: chevy tracker 4 cyl 4wd 2003

Most major auto part chain stores have a loaner code scanner (they require you to leave your ID while you use the tool in their parking lot). There is a connector under the dash near on the drivers side that accepts the reader....check the codes and Google them for repair info or post them back here.

SOURCE: The idle speed on our 2004 Lexus RX330 is 500 rpm.

unless you have the capability to reprogram the computer you can't, they are all preset programs

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SOURCE: I have a 2003 chevy

That means its not meeting the minimum thermostat regulating temp. Its saying that its not warming up.. If it feels like its as hot as usual. Its probably the temp, sensor.