lately my 4runner has been idleing wierd. just when it gets up to operating temp. when i stop it wants to idle up & down with my foot on the brake , but when i take my foot off the brake it idles high ,around 1500-1800 r's . iv'e checked vac. line and no leaks ,the brake booster seems to be ok .

the things i haven't checked yet are compression ,or injectors. i don't feel like doing a head gasket or timing chain r&r yet. it still runs like normal with no noticeable power loss. any thoughts ? i got the week off so i can tinker with it this week . thanks !

 

This has been covered a lot. I know because I always reply to them. You're probably low on coolant and/or you have the idle set too high. Probably a combo of both. IF the idle is set at 1000 or more and you step on the brakes with the clutch disengaged (pedal depressed) then the ECU will think you are stopping so it cuts fuel to the engine. It does it over and over which gives you the surging rpms.
If you're low on coolant then the idle air control valve, which is controlled by the temperature of the coolant, will remain open, sometimes more than needed so your idle is high.

 

x2 on the idle being high with ecu brake cutoff.

 

Turn your idle down. Worked for my 87

 

thanks guys! will look at the coolant level in the a.m. as i just recently changed the alternator on it . that would be the most likley cause.

 

well checked the coolant , it was low so i topped off the rad, it still does it ,altho a suspect i may have an air pocket that is still trapped some where . will check the idle speed too altho i was idling at around 800 r's before this started happening will do more tinkering in the a.m. could it be a stuck thermostat ? thanks for any help again.

 

 

mine does this too. seems to be getting worse. surges up to about 13-18k rmps, then drops down. surges up and down more often now. then sometimes it will idle at about 1800 2000 rpms. wierd thing is that it doesnt do it at all when the ac is on...