on a cold start up, it idles at 1500 and then drops down to around 500. the engine dies when down shifting into 1st and in reverse. any suggestions to what it could be or how to fix the problem? I just changed out the alternator two weeks ago. any ideas?

 

Check for vacuum leak(s).

 

I am having the same problems with mine. Possibly the compression.

 

Hmm shot in the dark because my 91 blazer did similar stuff but fuel pump taking a crap?

 

you got a full atmospheric bov?

 

is it just when cold? clean the throttle body and check for vac leaks

 

Ok.. I took it out today for Spin around the block, nor adjusting anything and it still idles low but hasn't died out.

 

mines acts similar except just when driving up a hill like my driveway my 06 sti dies out. weird. cant seem to find the problem yet.

 

you never answered my question. also have you had it tuned and what mods do you have? I've had this happen from 2 things, a bov that would make the idle dip and a bad tune that had the car running lean when it was cold. once it warmed up it ran fine but until then it was not drivable and would die out if i tried to go anywhere.

 

had the same problem. VTA BOV with a pull through MAF, if it opens at a low idle will cause the motor to think it is getting more than than it really is. Are you running a wideband, and if so, are you running rich at idle??

 

Just to check a suspicion, you do know that the 1st line on the tachometer is 500 rpm right?

 

Try cleaning your throttle body. If debris and dirt is accumulated around the throttle plate, this can lower your idle as well. Use throttle body cleaner not carb cleaner and spray on a rag then wipe the throttle plate edges and the bore of the throttle body. Don't spray directly into you throttle body though. Also if u don't have throttle by wire, locate and clean your idle air control valve.