Its a 99.5 a4 qtm, when coming to a stop idle rises to 1200 then slowly drops to 800. The only work i have done recently was replace crankcase breather, tb was spotless when i reinstalled it. Not even a CEL, Anyone have any ideas? Maybe idle control sensor idk, just seeing if anyone else has had this happen and what the fix was. Thanks

 

is u car misfiring a bit? if yes, then im sure u got a vacuum leak,
if not, could be you MAF. disconnect your MAF and see if the problem is gone.

 

disconnected MAF and it started bogging out, plugged it back in and idled fine. Im assuming that means its working properly. My boost gauge reads 12 to 15 vacuum at idle and 28 after pushing clutch in and coasting on highway. I did a boost leak test and thats how i found the major crankcase breather leak, there was another leak toward the back of the motor but i ran out of money to fix it. The car ran great even with the second leak, better throttle response, and quicker boost. The problem just started happening yesterday. I'll check the plugs and gap, but im not feeling a misfire and no CEL

 

i doubt your plugs are bad...
it might be a bad check valve

 

and yeah, your maf seems to be working properly

 

Sorry to thread jack but I'm curious....I don't have a cel for my MAF, but when I disconnect it idle changes a little but then goes back to normal. That means its not functioning properly?

 

i know this is pretty stupid to even ask, but just making sure you did a throttle body alignment...

why the hell would you disconnect it? you just cant start pulling random sensors just for the hell of it...

 

did u drive with no MAF on?
if your car drive fine (with maf) then you are ok.
when MAF gets dirty, it messes up your air flow, thats why the easiest way to see if your maf is bad is to disconnect it and see what happens...
if your car drives normal, then your maf is ok.

 

if you are having a problem beforehand like bad idle, misfires or bogging down- and disconnecting the MAF makes it better, then yes your MAF is bad. the car will run off of preprogramed software if there is no MAF input. If the MAF is sending bad information, disconnecting it so the car runs off that software instead makes it better.

 

Yea plugs were fine, and yes i did the TB alignment. I think the ecu maybe at fault here, ive had 3 bad experience's with chipped ecu's lol. Maybe i'll pick up another see if thats the case. Any reason a chip or the ecu would stop functioning properly? Like say timing chain skipped or something? IDk. If anyone can think of anything else for the main issue lemme know and we'll see how it goes! Thanks guys