horrible idle problem

i have an 89 exCab yota it has a 4 cylinder fuel injected when im at a complete stop the RPM`s go from 1g to 2g really fast up and down. but when i push on the brakes the RPM`s go from 1500 to 2000. does any one have any ideas that would cause this???

Vacuum leak!!!!

do you have an a/c? i have an 88 toyota where the a/c compressor seized up on it... i disconnected the a/c compressor and was going to hook my a/c switch up to my electric compressors for the air suspension. but i wanted to push the switch to see what would happen and without the a/c compressor hooked up when i pushed the switch in, the truck does exactly that. it goes up and down...the truck is looking a drag on the motor to compansate for but since there was nothing there it would just run up and down from 1000 to 2000. also, is your alternator good? i had one also go out a while back but i had to drive it through town for a lil while...it also will make the rpms go up and down like that because the battery is running low on power and the truck is going to try to spin the alternator faster to generate more charge. which also causes the rpms to go up and down. although my truck has a 22r this could be something worth trouble shooting. does it do it when your driving it above 2000 rpm? or when you push in the clutch to shift and let it come back down to idle while your driving? anyways good luck with it.

Check your coolant level, sounds wierd but it fixed the same problem i was having once on my truck.

check for vaccum leaks or your idle air control motor....that'll fix it one of those two

I replaced the alternator, looked for vacuum leaks, i have a/c but it don`t work it needed to be charged. so if i take off the a/c belt it might work??? i sprayed starter fluid on the vacuum lines andd nothin changed i also put a red top batterie in. im just really frustrated. any thing helps

check you IAC motor also do you have any check engine lights on or codes in the system. also any other systoms you could give would help, mass air flow sensors are know to fail on those years. did you spay cleaner into the sensor element?

whats an IAC??? i also replaced the pcv, the fuel charcol canister, alternater, unhooked the a/c, what should i try know???