new member here, so if this problem is very common, please point me in the direction of what causes it and how to fix it.

very wierd problem here...

a friend at work has a clean 85(i think) 4 runner, 22re, 5 speed, 4x4. just recently, whenever she would press on the brake pedal, the engine idle would immediatly drop down, the go back up, kinda like a bouncing idle, only unlike mr2s, instead of the idle raising higher than normal then dropping, this 4runner is dropping down to ~350rpms, then right back up to the normal idle. as soon as she lets off the brake, it idles completely normal.

here is the strange part, someone suggested that she pull the brakelight fuse... all the sudden, the bouncy idle was gone, stayed normal when she pressed on the brake pedal. she put the fuse back in, and there it goes, dipping down like before.

ryan
toymdngn (from the mr2oc.com place)
89na mr2
04 mazda 6
75 datsun 620 (50k mile stocker)

 

well, looks like some other guys are thinking what i was thinking at first. sounds like it might be an issue with the alternator. seems like the voltage regulator is "pulsing" on/off when the brake lights start taking power, and the alternator puts a large load on the engine, just long enough to make the idle drop down real low.

 

Idle speed is set too high, see this recent Toyota Trails "Truck Tech" column for the long answer:

http://www.4crawler.com/4x4/TLCA_Tru...ech.04.09.html