engine not happy
 

since i've bought the car about 6 months ago, it's always had it's little periods where it would idle up and down between 1000 rpm and nearly stalling,and sometimes it will die when i put it in gear. but now the problem seems to be happening more since it warmed up outside. also, my gas mileage is absolute crap. i consistently get 200 miles to a tank and it's killing me with the price of premium nowadays.but, every now and again it will get like 300 to 375 to a tank but it's rare. the only thing i've done is bypass the throttle body coolant and put in a k&n airfilter. i run fuel injection cleaner all the time and keep the throttle body clean and so on. i just changed the pcv valve too. any help would be great.

The number one cause of a bad idle, in my opinion, is a vacuum leak. I'd start there.

Is the car ever difficult to start?

no the car is never hard to start and i have no vacumm leaks that i can find and i had the dealership look too. the ones they found got fixed.the idling thing doesn't happen constantly it's just starting to happen more often now.

First off, quit using f.i. cleaner all of the time. Gas has detergents already in it and the fuel pump and injectors rely on the fuel for lubrication. Once or twice a year is fine, more than that is overkill and potentially harmful.

The problem you're having could be crud built up in the IAC (search cleaning the throttle body - it has to be removed to clean properly) and throttle body, the MAF could be going bad or dirty (search cleaning MAF and use of aftermarket filters.) It could also be a coolant sensor going bad. Since your mileage is suffering, I'd concentrate on the MAF and coolant sensor.

Like Beav alluded to - my guess would be oil on the MAF sensor from that k&n.

anybody know how to check the coolant sensor and where it is? i'll try claning the mass airflow today and get back to you on that.the throttle body will have to wait for another day.

i cleaned the mass airflow with electronics cleaner and unhooked the battery for a few hours just for the fun of it. it seems to be running better but we'll know for sure probally tommorrow if it really helped.it usually doesn't do it until the computer learns alittle then it goes to crap. it did try to stall once though as i pulled into a driveway so chances are something still needs some work.this car is so damn tempermental!

ok so today i set the throttle position sensor at .505 volts and drove around for awhile. after cleaning the mass airflow and setting the tps it is definitely running better but the fuel economy still hasn't seemed to improve. i'm still getting just 25 miles to a eight of a tank! but it's too soon to really judge it yet. i'll see hows it's done by the end of the week and report back.

weel still no big improvement in mileage. 100 miles to a half tank. this blows! my trans am had a 350 in it and far from stock, would smoke 99% of cars i came across and got 17 to 24 mpg at all times! even with burned out maf sensor! this is lame as hell. the idle problem is definitely fixed for now though. someone help with ideas please.

Sometimes it is better to just have the car checked out by an experienced mechanic than to just throw parts and choice words at it. The money spent should be recovered quickly considering the amount of gas you are using.

i had the car checked out by my subaru dealership and they say theres nothing wrong. no codes in the computer and so on. they say it's not gonna do much better than that because it's so heavy. whatever! the trans am was 150lbs. heavier!!! makes no sense to me. I took a drive today to my moms and the idle problem started acting up again, and i got about 160 miles to a half tank on mostly highway travel. i'm starting to think the maf sensor is just screwed up enough to ruin my mileage but not trigger the ses light. what do you guys think??

Don't forget that the gas gauge is vauge at best - what is your MPG doing?
I had an idle hunt too (after foolishly trying to clean the IAC the quick way) - then I did it the "proper" way!

Matt

Care to elaborate?

Due to the IAC being underneath the t-body the only proper way is to remove the assembly.

Since you havnt had the car long, I'd try unhooking the battery for a while to reset the ECU. It's possible the privious owner ran crappy gas and the ECU is adapted to it. Unhooking the battery will clear its memory and make it relearn. Just make sure your running good clean gas (no additives from a bottle). At the least it'll improve the power, and it doesnt cost you anything.