Installed BFI Stage 2 Chip, ran great for 4 days, now idle problems & rev hang

[Fast VW]

In my car the only time I had issues with the rev hang and flakey idle was when the out side temperature was below 60 degrees. So I unplugged the IAT sensor and all of my issues went away.

When the IAT sensor is unplugged the ECU uses a default constant temperature and then makes all "corrections" according to the default temperature. I do not recall what temp the ECU uses but it is in the bentley manual. If I have time later I will look it up and post that temp.

My guess is that when the outside temp gets lower, the ECU is making incorrect "corrections" to the fueling based upon the C2/BFI chip commands. But when the IAT sensor is unplugged it is making corrections based upon the higher "default" temp.

Before anyone says it, I did replace the IAT sensor with brand new one and it made no difference. The only issue I have with the IAT sensor unpluged is a CEL.

C2/BFI - Please fix the correction factor in the chip programming for lower air temps.

[vacuumnoise]

In my car the only time I had issues with the rev hang and flakey idle was when the out side temperature was below 60 degrees. So I unplugged the IAT sensor and all of my issues went away.

When the IAT sensor is unplugged the ECU uses a default constant temperature and then makes all "corrections" according to the default temperature. I do not recall what temp the ECU uses but it is in the bentley manual. If I have time later I will look it up and post that temp.

My guess is that when the outside temp gets lower, the ECU is making incorrect "corrections" to the fueling based upon the C2/BFI chip commands. But when the IAT sensor is unplugged it is making corrections based upon the higher "default" temp.

Before anyone says it, I did replace the IAT sensor with brand new one and it made no difference. The only issue I have with the IAT sensor unpluged is a CEL.

C2/BFI - Please fix the correction factor in the chip programming for lower air temps.

yeh the IAT unplug works for me too, I already had a CEL with it plugged in, so thats no big deal for me...

I'd rather not have constant rev hang...

[vacuumnoise]

just checked the bentley, with the IAT unplugged "the ECU will simulate a fixed signal based on an engine temperature of approx. 68*F (20*C)."

[vacuumnoise]

also here are the code/s I had since i installed the BFI stg2 chip

OBD II Code P0172 and P0175
Fuel System Too Rich (Bank 1 or 2)

Our emissions expert has put together the following information about the P0172 and P0175 fault code. We have also included diagnostic procedures you can take to your repair shop if the mechanic is having difficulty analyzing the code.

OBD II Fault Code

* OBD II P0172
* OBD II P0175

Fault Code Definition

* OBD II P0172 Fuel System Too Rich (Bank 1)
* OBD II P0175 Fuel System Too Rich (Bank 2)


not sure if it was both, or one of them, I just rememed "data bank rich"....

more info here, a lot of good info actually: http://repairpal.com/OBD-II-Code-P0172-and-P0175

[Fast VW]

Two points of interest:

One of my cars is using C2's stage 1 FI software and has no issues at all.

The car using the NA software has the idle and running rich issues but only when it get's colder outside and the engine is not fully warmed up. Also these issues are only present when the motor is going from a higher load to a lighter load. In my case when going from D to P or N. It seems for others it is when the clutch is pushed.

I still think this is a fueling issue like I did when this post started but I think it is a fuel map when IAT are low and engine load is light.

But what do I know.