hey guys, got a small problem i need some help with so i can diagnose whats going on ..

my tc is having idle issues, i cant figure out what it is ..

i just hooked up a wideband..

now, sometimes the idle is fine, but other times like when i come to a stop after boosting, the idle bounces between 500 or lower rpm and 1,000 rpm

and it bounces up and down for a little while before stabilizing itself.

i have a small 16g turbo kit, with a aem fic tuned,

can anyone tell me what would cause my idle to be rough like that ?

according to the wideband it bounces between 12.5 afr and 16 - 17 afr

 

could it have something to do with your blow-off or bypass valve system? when your releasing boost, can't it cause problems with the maf sensor readings, but your letting the air out?

 

the kit you have whats the name?

 

it's a custom kit ..

all jdm parts

 

from what?

...

 

JDM parts? How did you manage that?

 

all jdm parts? must have been a hell of a custom kit. did you like send your specs to japan to have them make the piping and such to fit under your hood?

anyway, list some specs of your kits, like turbocharger, what type of bov or bpv you have, open dump, closed dump, recirculating, etc.

 

I bet its venting atmospherically or you have an exhaust leak or clogged cat. One of those. Also check for a VAC leak.

 

this is going to sound completely irrelevant but my '96 cavalier z24 (stock). did the same thing...some days, the idle would bounce enough to choke the engine down (sometimes i would get a misfire CEL, other times not)....i put about 200$ in it trying to resolve it but no luck(new coil set, ect)...fianlly i remeber that i had switched spark plugs to "high performance" plugs when i bought the car...so i bought wat chevy called for and the ceramic insulation on the oem plugs was bigger then the aftermarket ones...switched out and everything went back to normal..i found blacked spots on the valve cover/head where the spark was shorting out and not going to the cylinder....so i would check all of your electric connections.....

like i said, it sounds irrelevant but i had the same problem...and it would go away for months at a time and then come back and be consistent for weeks....

so check your electrical system...it may save you some money in the long run if that is the problem...

good luck..

 

umm i think all tc's does that. mine does and my turbo kit is still in the box. like when you your slowing down with the clutch in it will be around 1200rpms the gradually come down. or even some times it will drop really low to about 500rpms for a few seconds like its about to stall then pick itself back up. but my mechanic says thats because my battery is dieing because of the 1200 watt amp i had running off it.

 

jdscion, try a capacitor...i had a 1000w system in my old car.and i could watch my idle drop and lights dim when it hit hard...i bought a 1 farad cap and it caught most of the bass hits so that it didnt affect my car.

i heard that a rule of thumb is 1 farad for every 500rms/1000peak Watts..dont hold me to that though

i think he means pulsing when already stopped.. ^^i know what your talking about..im bone stock and mine will drop to 500 once and pick back up if i put in nuetral after cruising at higher rpms..but it only drops once..and then compensates back to idle..

 

blowing off to atmosphere will cause the car to run rich. running rich will probably tell ECU to pull fuel, pulling fuel when it really ISN'T running rich is probably going to cause fuel trims to go stupid. causing fuel trims to go stupid is going to make idle rough.

jdm does not exist for a USDM car.

 

the pipes are custom mandrel bent pipes i had done at a friends shop, i made the mistake of putting the blow off valve after the maf sensor causing it to run rich after blow off to atmosphere.

the turbo is a 16g turbo, set at 7 psi with a tials wastegate.

everything else is custom made. doesnt look as good as most kits sold on the net, only cause my piping is not a nice looking setup ..

anyways ..

my idle is rough sometimes and sometimes it isn't .. i dont know why though ...

 

I have the same exact problem but usually during a cold start. After it has warmed up then it is not as bad but I still get idle surges when trying to idle while moving. When the car is moving the ECU idles at a different RPM then when it is stopped.

Also JDM mean Japanese Domestic Market. This means to have a JDM part it must be for a stock car in Japan. Since the tC is in the US only then there are NO JDM parts for our cars.

 

why yall talkin bout BOV's? OP, ur talkin about running rough at idle as in, ur car has BEEN sitting say, at a light, then it idles rough then comes back up and then later the light turns green? a BOV does Nothing at Idle. tru, between shifts is vents air that was metered by the MAF to atomosphere and that lack of air means that the fuel that the ECU sent meets nothing to mix with for a sec which is why it pulls everything back lean until the BOV closes and everything is "ok" again. but at idle he is in vaccum and that BOV aint doin buthin but being pretty.

if i were u i'd check for a vacuum leak and also plugs like was mention earlier. also check ur 02 sensors if u dont see anything wrong with the other stuff mentioned. maybe they are washed out and sending funny signals. btw all tCs idle rough momentarily sumtimes. now BOUNCING shouldnt be happening as in 1k rpms, 500rpms,1k,500,1k,500. u mind being a bit more specific? and does it ever do it without u getting in boost first? and how often? Every drive? numerous times every drive? once a week?

When was the last time u got tuned?

 

BOV to atmosphere symptom.

 

My old Tial BOV used to open slightly at idle. When I switched to a HKS BOV my idle improved both while moving and at a stop.

 

so .. maybe it's my ____ty BOV

 

What kind of BOV do you have?

Push-pull systems will not cause an idle problem. The piston type TiAL designs can if the spring is not holding shut properly at idle.