Originally Posted by scott@upsolute
the ECU has strategies: ex. on cold start coolant temp and IAT can be compared...on a cold engine they should be about the same...
I'm not saying that toying with the IAT isn't a dumb idea, because I believe it is...
However, I do disagree with the fact that the ECU will throw a code during startup if the coolant temp varies too much from the IAT. In variances between the coolant and the IAT, there are only 3 possibilities, they are the about same temp, the coolant is warmer or the IAT is warmer...
In the first case (~same temp) there should be no code thrown as this would reflect a cold engine starting normally.
If the ECU threw a code in the second case (the coolant being warmer), the ECU would throw a code every time you started a warm engine.
In the final case (the IAT being warmer), well lets just say that if you purchase this mod and it makes your IAT read warmer than your coolant, you've been robbed.
With all that being said, *some* GM ECUs are programmed to recognize that if the IAT reading is -20 degrees, your coolant temp should not be able to reach 185 degrees when it's that cold outside unless something is wrong. However this only happens about 8-15 minutes after the car has been running and takes about 40 miles after that to clear.