[GPeter]

Hi guys,

I'm new here. I have just started to create my own (customized) boosterplug like device. I decided to approach the problem on scientific way.

At first I started to measure the characteristic of the original IAT sensor. It seems the R25 value (resistance measured on 25 Celsius) is 5K.

Next decide how much fuel do we want to add. Boosterplug says it makes +6%. I think it is a bit too much. I don't want to kill my catalytic converter. Lets say +4% should be enough to smooth the low rev behavior.

If I want +4% more fuel the IAT sensor must say the weight of the incoming air is 4% heavier. So the temperature should be 4% lower. At 0 Celsius (273 Kelvin) should lie 11 Celsius colder air.
At 27 C air temperature this value is 12 C.

To combine the original IAT chart and the required offset chart we will get the new chart which describes the modified characteristics. Finally subtract the original and the new resistance values and you will get the additional serial circuit parameters.

As far as I measured the slope of the BMW IAT sensor is not as steep as the NTC resistors can be bought. So if you use simple serial NTC it results more fuel than expected in the very cold and less fuel in the warm. That could be the reason to use parallel resistor in the boosterplug.

That is the theory and let's see the practice.

I wouldn't want to dig the internet for connectors so I just cut the wire goes to the IAT sensor. I know it is rude but cheap []
I had no NTC at home so I installed a simple resistor first. The value is 2.2K. It is suitable for the 25-30C range. If is just a temporary solution but good for the first test.

The first results are quite impressive. I haven't experienced cut off during the ride before but sometimes the engine stopped after cold start. This phenomenon disappeared. I feel the low rev range is better now as I expected.

Now I am here. I already ordered 2.2K NTC thermistors and continue the tests with different temperature environment.
I try to access to a climate box to make more precise characteristics about the IAT and the modified circuit. I plan to build in a switch temporary to make sure it is not placebo.

I'm getting back later to share the results and plan to make a step by step guide about this modification.

Waiting for the comments and sorry for my English.