This issue seems familiar to mine; I am just a layperson, not a mechanic and i am wondering if my situation is similar. Here is my situation: My brother and i wanted to replace the a/c compressor thinking that it might be the culprit for the lackluster a/c issue. Well before we even try to unplug and or change anything, my '98 Audi A4 was running perfect. So after tinkering with the a/c compressor but not taking anything out except for my brother unplugging something that connects the compressor to another part of the engine; changing the oil; checking the fuses to see if any of them malfunction; all of this was done after my brother disconnected the battery. So essentially after all of this, the car was able to start except that it couldn't run pass a certain RPM and not as it used to before we did all the above and a code P1545 came up. And so the day after that, we couldn't start the car anymore; and it seems like there is some smoke coming out when we try to start the engine. Anybody out there who is nice, knowledgeable and is not fazed by my long story, please assist me in any way, shape or form. Thanks and i hope this is not the beginning of an expensive repair for me.