i noticed stopping at a light the car started shaking just a bit, looked and noticed idle was hovering arounf 530-550rpms (got a 5spd by the way). im pretty sure it should be around 625-650 and now its low out of no where. what could be wrong here?......oh btw i installed my stock catback back on 2 dyas ago, but i doubt it would be the problem.

 

Possibly and hopefully not, engine coils. ever changed them before?

other best guess is MAF

 

plugs coils changed about 1.5 years ago, MAF about a year ago. i actually hope its the maf and not something worse, but cant think what else it could be....havent messed with anything for a while

 

My idle is just passed the 500 rmp mark and i changed maf and coils 3 months ago. Car doesnt shake unless I rev the engine and quickly let go of the acclelerator in park. The needle may drop below the 500 rmp mark at some instances.

 

iacv......

 

sound like you might need a new MAF

 

very unlikely it's the maf.

reset the ECU and see if it does it. then i would second the IACV probability..

ps. what octane are you using? cause if its 87, well there is your problem