General New build 4G63 running lean

[Craig13]

I recently got my car running after a full engine rebuild. AEM AFR gauge will read 14.5-15.5 ish on initial start up but the car will begin to raise idle speed to around 2k on its own after a few seconds. When this happens the AFR gauge pegs out and reads three flat bars (over 19:1). I can sometimes get the idle to come down by blipping the throttle a bit but it will only come down to around 1k - 1100 RPM. It will also occasionally surge up and down. I have boost leak tested the entire system and fixed all leaks I found and the problem persists. I also have the BISS turned all the way in currently in an effort to control the super high idle but 1k is lowest it will go. I know it typically should be somewhere around 2 full turns out. I have also had a friend connect his AutoEngenuity (ECU reading program) to it and he said that all sensors are reading correctly and fuel trim seems right. I am at a loss at this point and don't know where else to look. Everything seems to be pointing to a vacuum leak somewhere in the system but I cannot find any leaks. Also, it is on a stock ECU. Any help is greatly appreciated!!!!!!!!!

 

[DSMPT]

Sounds like you have some vacuum leak around throttle body but as you mentioned you fixed all leaks, maybe the stop screw is not adjusted properly. Should check it if you haven't done it.

 

[Craig13]

I thought the same. I actually just replaced all seals and gaskets on the throttle body a few days ago. Are you referring to the BISS screw? The one on top of the throttle body next to the TPS?

 

[dondmon]

I'd place my money on vac leak as well. What about the tps calibration also? Did you look at that when you had your ecu reader hooked up?

 

[Craig13]

We did calibrate the TPS while it was connected yes.

 

[DSMPT]

Are you referring to the BISS screw? The one on top of the throttle body next to the TPS?

No, not the BISS. If you have a 2g throttle body, the one in the green circle in the pic below (A screw with a lock nut). If you have a 1g throttle body, with the idle switch.

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[Craig13]

Uuuhhhhh I don't have that screw on my throttle body... or the spare throttle body that I have. How would that cause a lean issue though? Sorry for my ignorance.

 

[DSMPT]

Hard to tell how much it is related to your issue, you may have another issue as well since you said it's the first start-up after rebuilding the engine, but I can say without the screw or without locking by the lock nut, you may not have a stable idle and you feel the throttle plate stuck when you want to open. So anyways you should have it and set properly. Also should check throttle cable adjustment.

 

[Craig13]

Okay. I am going to get the replaced in the next day or so and see what that does. Thanks for the info! Any other ideas are greatly appreciated.

 

[jed344]

What throttle body is on the car? I have learned a long time ago if a factory mistu one and coolant lines are not hooked up this happends unless FIAV is disabled.

 

[Craig13]

I am running a factory mitsubishi TB and do have the coolant lines connected. Still fighting this issue with no progress...

 

[Vegas Smith]

The stock the idle control can't really cause the car to idle at 2k so you're looking at a mechanical issue with the throttle cable not being adjusted properly is my guess. As the car warms up the throttle expands and will pull the throttle open. Always set your throttle cable up when the car is FULLY warmed up with a heat-soaked engine bay. The afr climbing to 19 really concerns me too. It's hard to say what's causing that. Is the wideband not installed correctly? Is the sensor dying? It's hard to say.