Idling issue... have tried various things

[enixxi]

Hey, I have an s13 with a redtop sr20, blitz fmic, 3 in turbo back. I just moved to arizona and drove the car all the way out with no issue, but after a few days my car's idle started stumbling. What would happen is I would drive the car around normally untill around operating temp. which according to the gauge is under 80 C. Once it was warmed up it would run and boost fine, but the idle would stumble and the car would shut down. It would fluctuate between 0-900 rpm almost shutting down or actually shutting off.

At this point I tightened up all the intercooler piping, replaced the vacuum hoses and made sure my maf sensor was well grounded. After the intercooler piping and vacuum hoses were replaced the car stopped shutting down. Now 3 different things can happen when the car is idling.

1) It idles fine
2) The rpm drops to about 200-300rpm and my fpr gauge reads 10.0
3) the rpm fluctuates between 0-900 rpm almost shutting off, but barely staying on

These symptoms occur randomly during the same driving session with the fluctuating idle being the most common. The last thing I've tried is switching O2 sensor's with my buddy's O2 sensor and the same thing still happens. Has anyone had similar problems or have an idea as to what can be wrong?

[KoukiMonsta]

check:
TPS
MAFS
coolant temp sensor
codes


what mods? FPR?

[Z U L8R]

tighten up your blow off valve and mechanically raise your idle just a tad with the idle adjustment screw inbetween the intake runners of cylinder 3-4. it's plastic so don't strip it, loosening it raises the idle. bump it up to say 900-1000

i'm assuming your maf is before the turbo on the intake snorkel....basically your problem is because your blow off valve vents out to the atmosphere.

your mass air flow sensor measures the air entering the engine and relays that information back to the ecu. the ecu then adjusts by giving it the corresponding amount of fuel. well when you let off the gas and your blow off valve opens and you coast to a stop in neutral it releases a chunk of that measured air out into the atmosphere. that leaves you with too much fuel and combined with a relatively low rpm the motor will choke and stall.

so you can tighten up the blow off valve spring so it shuts sooner and leaves a little more air in the engine as well as raise the idle, which also allows more air into the engine and that will lessen the chances of the rpm dropping so low that you have to feather the gas to keep it from dying.

the other fix is to put your mass air flow sensor in your intercooler piping a little in front of the throttle body. this is called "blow through" , then you'll put your blow off valve a little in front of your maf, or just anywhere in the intercooler piping in front of your maf.
now your blow off valve can do what it wants to do, your turbo can do what it wants to do, and you can pop off intercooler pipes all day long and as long as it's in front of the maf, all the air entering the engine is still being accounted for.

i would suggest though that you wait on doing blow through until you have something to tune with just for safety measures.

hope that helps, best of luck

Dave

[enixxi]

My blow off valve is resurculated so that is not the problem... What I have done since my last post is I cleaned the IACV and the car ran better for a day before returning to similar but not as drastic problems. I then took the iacv off and cleaned it even more. I also cleaned out the uim and lim which both had carbon deposits. Since I put it back together the car has been running fine, although I did have it stumble once a day after everything was back together. This stumble was an 800-300-800 rpm stumble. If I had not been paying attention closely every time I drive I wouldn't have even noticed it. If the problem develops again shortly does that mean my iacv is actually shot? It's only been about 3 days since I got it back together so I will continue watching it.... Maybe turning up the idle if it starts again? My idle screw is metel so I'm not too worried about stripping it if I have to mess with it.

[enixxi]

I've also been thinking about doing what Z U L8ER said about the maf sensor.... But if the maf sensor is in a different location, say right before the throttle body, shouldn't the airflow be the exact same as it is right after the air filter where the maf sensor is currently located? And if so then shouldn't the tune not be affected if the sensor is moved closer to the throttle body?

[Z U L8R]

it does affect the tune slightly because instead of the cool air being sucked into the maf, hotter air (because it's compressed, hence why you use an intercooler) is being FORCED through the maf, so yes it will affect the tune.

Dave

[rebornS14]

coolant temp or bad iacv maybe.

[enixxi]

since I ripped apart the iacv and cleaned it all out very well the car has been idling fine. Guess something was just messing with the iacv.Thanks for all the help