Weird idle problem!

[mikevar94]

So I really don't know where else to go from here. The car has had this problem since I bought it. Now, the car has a mind of its own and idles all over the place. But it's always random. Sometimes it idles extremely low like its about to die and other times it idles up at 2500rpm and sometimes back and forth. I can also smell like its running rich. I was convinced it was a vacuum leak but a mechanic told me it doesn't sound like one if its not rough idle constantly. I tried spraying carb cleaner while the motor runs and came up with nothing except for up in the fuel rail by injector 2. I only got it once and after that got nothing. I don't know where else to go from here. I'd try a boost leak test but it boosts fine! It drives pretty nice except for weird throttle response that also COMES AND GOES. if it helps it has idle surge as well as any other dsm. Any ideas?? I plan on hitting my 300whp goal soon but not until I fix this problem!

 

[eclipsyco]

Any CEL.?
Most likely is your ISC aka IAC. Sometime it might throw a CEL sometimes not!

 

[untouchablecc]

You can try unplugging the Idle Speed sensor connector and see if it makes it run worse or better. Its kind of primal way to diagnose the issue but if the idle doesnt change its probably bad. Another thing is the FIAV (fast idle air vale) which is inside the throttle body and likes to fail after many years of use. Its a wax valve that moves based off coolant temperature. I think it opens as temp drops and closes when the temp goes up to raise and lower the idle for cold start conditions. When they start to fail they will still move but sometimes get hung causing higher idle. It can be blocked off but Id start with checking the ISC first and go from there.

 

[mikevar94]

Any CEL.?
Most likely is your ISC aka IAC. Sometime it might throw a CEL sometimes not!

Nope codes. And I'll check it out and get to you. Does it sound like any kinda of a boost leak to you?

You can try unplugging the Idle Speed sensor connector and see if it makes it run worse or better. Its kind of primal way to diagnose the issue but if the idle doesnt change its probably bad. Another thing is the FIAV (fast idle air vale) which is inside the throttle body and likes to fail after many years of use. Its a wax valve that moves based off coolant temperature. I think it opens as temp drops and closes when the temp goes up to raise and lower the idle for cold start conditions. When they start to fail they will still move but sometimes get hung causing higher idle. It can be blocked off but Id start with checking the ISC first and go from there.

So should I unplug that sensor while the car is running? Also can thr fiav be changed?

 

[eclipsyco]

Nope codes. And I'll check it out and get to you. Does it sound like any kinda of a boost leak to you?


So should I unplug that sensor while the car is running? Also can thr fiav be changed?

I does sounds like a boost leak as well but since you already did a BLT I didn't want to mention it again but usually a weird idle and rich condition are due to boost leaks assuming you're stock. Check the ISC which is really easy unplug it with the car off (it will throw a cel if you unplug it) also check all the vacuum lines in that area for crack and/or missing (EGR, the three solenoids on the firewall and the lines to the intake).

 

[PlanZero]

Not sure of this is applicable on a turbo, but did you check the TPS or BISS?

 

[bw2277]

Yeah +1 on the biss and tps...check for proper adjustment I just had same issue.

 

[mikevar94]

Not sure of this is applicable on a turbo, but did you check the TPS or BISS?

I replaced the tps about a month ago and nothing happened. I adjusted the biss screw but no matter what the system compensates plus according to the how to properly adjust the biss screw thread Im doing it wrong without using a scan tool. Also I never did a boost leak test just to clarify.

Also, I unplugged my isc sensor and the idle made no difference. Did the same with the map sensor and still no difference.

If I had a boost leak, wouldn't I not be reaching full boost? And wouldn't it feel "un smooth" under boost because right now it boosts fine

 

[Lou98GSX]

you could also have a bad upstream 02 sensor. it could get stuck rich and not throw a code . it will also effect throttle response .

 

[untouchablecc]

I replaced the tps about a month ago and nothing happened. I adjusted the biss screw but no matter what the system compensates plus according to the how to properly adjust the biss screw thread Im doing it wrong without using a scan tool. Also I never did a boost leak test just to clarify.

Also, I unplugged my isc sensor and the idle made no difference. Did the same with the map sensor and still no difference.

If I had a boost leak, wouldn't I not be reaching full boost? And wouldn't it feel "un smooth" under boost because right now it boosts fine

Did you unplug the MDP sensor ontop of the intake or the MASS airflow sensor? If you unplug the MDP sensor it wont do anything anyways. Ive drove cars for years with a 6 bolt swap and that unplugged.

As far as the biss screw goes your supposed to let the car get up to operating temp, screw the biss screw all the way down then wind it 3 complete turns out and thats your starting point. It doesnt sound like its fixing your issue anyway. Im willing to say its your ISC. Try taking the ISC out and plug it in to its connector. Have someone turn the key on and watch it to see if it starts clicking and motorizing. If its not its dead. Your might be able to clean it off and it might fix id try and find a spare and switch it out. I have many throttle bodies laying around so I can do that kinda trial and error. Im not sure if you have a buddy with any or access to any.

 

[mikevar94]

Did you unplug the MDP sensor ontop of the intake or the MASS airflow sensor? If you unplug the MDP sensor it wont do anything anyways. Ive drove cars for years with a 6 bolt swap and that unplugged.

As far as the biss screw goes your supposed to let the car get up to operating temp, screw the biss screw all the way down then wind it 3 complete turns out and thats your starting point. It doesnt sound like its fixing your issue anyway. Im willing to say its your ISC. Try taking the ISC out and plug it in to its connector. Have someone turn the key on and watch it to see if it starts clicking and motorizing. If its not its dead. Your might be able to clean it off and it might fix id try and find a spare and switch it out. I have many throttle bodies laying around so I can do that kinda trial and error. Im not sure if you have a buddy with any or access to any.

The mdp sensor is the one right on top of the intake right? If so then yeah that's what I meant by map sensor. As far as the isc sensor I unplugged it then replugged and I didn't notice any sounds coming from it. Will it be real noticeable? As far as it making a difference with the idle..it was about the same with it plugged and unplugged.

Also, the o2 sensor in the engine bay was replaced a couple months back and still no difference.

This problem really worries me because someone told me that the smell of running rich is similar to the smell of running lean and I don't have a wide band yet so I wanna make sure I'm not leaning out from this.

 

[Ozyeclipse]

Check your maf some idiot maybe thought like he could get a .005 of a hp increase And messed with it
My 1g was is in the same state,had a lower honeycomb removed
I have a 1g maf-t set up now but it still idled high around 1500-1800

Not sure in 2g's but people often mess with these things for a slight miraculous power increase that not only is stupid and useless,but it messes with your idle and fuel trims!

 

[raybugarin82]

Have the same problem and replaced parts connected the problem....turns out i need a new ecu...try replacing it and see if it helps