Everytime I start slowing down to come to a stop and put the car in neutral and start braking, the RPMS surge. they'll fall to where they should be initially, but then they'll surge to 1500-1650 and come down to 1100-1200 rpm then bounce back once more before eventually stabilizing.

Why would this be happening? I initially thought it was because of the cold weather but it was 75*F today and it still did it.

Also to note, I did do a 25psi boost leak test today and am still getting the same problems. Also, I am having very rich idling, around 10.9-12.0. I don't understand how this could be happening, my tune is fine and the idle tables are fine too.

Could it be me idle air control on its last legs? I really don't want to buy one as a) it's expensive b) if I end up not needing it I can't even return it

Any suggestions?

 

what are your fuel trims like?

if you fixed a boost/vacuum leak then you fuel trims would be way out...

anyways if your fuel trims are way out then reset the ecu and see if that fixes your rich idle..

 

+1

 

Well since we did the boost leak, we disconnected the battery afterwards anyways (since we disconnected the MAF and had the car on to power the boost gauge to watch it)

Anything else?

Thanks for the input!

 

If the car was running ok before, i would assume that maybe one of your sensors are not working properly. The sensor is probably is back a voltage signal thats not correct.

Example: your car is warmed up but your coolant temp sensor is still showing that the car is cold. thus no check light since there is feed back from the sensor.

sensors that affect AFR are:
- oxygen sensor
- coolant temperature sensor
- air temperature sensor which is part of the MAF

Monitor your sensor readings and see if any are out or acting weird

also check to see if the vacuum that the car pulls at idle is the same or if it has dropped off. if its low make sure your timing is ok or maybe you have hurt your engine

 

I've had a bad o2 in my STI before and it's easily noticeable and the car drives like ***, but this isn't the case. While coming to a stop as soon as I put my car into neutral (it's still coasting) it'll go extremely rich until it finds its way and will then idle between 13.5-15.4

Sometimes it'll struggle and dip to around 600-700 rpm and go real, real lean, but most of the time it's just rich, like when the idle rpms start to come up it'll start getting rich then fall back to where it should.

The vacuum is the same, the car still makes good power and everything it's just the idle. It's not eating oil or losing oil for that matter.

 

Sounds like your maf is bad, try switching with some else. Like everyone else said post up a log of your fuel trims @ idle and cruise. For idle your going to select low fuel trim and cruise select mid fuel trim, also make sure to select o2 feedback as well for both trims. I found using mitsulogger the best for logging fuel trims.

 

I just had the MAF cleaned yesterday. I'll make some logs at idle and cruise soon and post them.

 

make sure you give it some time when you log trims. I say about 5min for idle and 10 min for cruise.

 

Like 5 min after I turn the car on or 5 min of logging?

 

5 min after logging I would do 10 min on both idle and cruise to get good #'s. Fuel trims cycle every 4 mins.

 

so you cleaned it and then your car started acting up or vice-versa?

basically if you are getting funny lean/rich conditions at idle (when warmed up) then it can only be a few things, o2/maf/injector scalings/fuel filter?

 

i had a similar problem a while ago but i changed my tune and it went away lol idk wat i changed but it fixed itself i guess

 

No, I cleaned the MAF after it started acting funny in hopes of curing it. I don't think it's injector scalings because it's been left un-touched as I'm on the stock injectors. Fuel filter is interesting, how often should the be changed? And as for the o2, wouldn't more severe symptoms show up if it were on its way out or already out?

Thanks for all the help everyone!

 

i'm at 52k and i've never changed my fuel filter lol infact i havent even seen it lol someone wanna touch on where it is for op and myself