fluctuating idle

[old sub freak]

hello, Just got a 1999 imprezza outback..nice rig but..... When you first start it up the idle bounces up to 2,000? and down ..Only for a few seconds? any ideas,thanks <todd      oh ..its a 2.2 automatic

Edited August 29, 2019 by old sub freak

[rverdoold]

Could be couple of things to start with:

• Coolant temperature sensor incorrect
• Manifold pressure sensor incorrect
• Throttle position sensor incorrect
• Vacuum leak (this would also result in normal rough idle)

Those sensors can be tested on resistance, vacuum leak can be checked by closing the air-inlet before the filter with a or something that can close of the inlet. The engine will starve of air and stop. But if there is a leak it will make a hissing sound.