If I drive my car with the a/c not engaged everything is fine. I could drive forever and not have the CEL come on. But everytime I turn the a/c and it runs for a few minutes the CEL light comes on and gives me a fault 11 code for air injecton system. I reset the code and drove with the a/c off.........for a few days as a test, then I turned the a/c and within minutes the code was back. I reset the code and then drove the car again with the a/c and the code was back in a few minutes. And just to make sure it wasn't coincidence I rest the code yet another time drove with the a/c off for about 45 minutes then I turned the a/c on the code was back. Anyone know what this is all about?

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1990 190E 3.0L