Recently replaced battery, ran great before; now, not so much! '99 A4 1.8t. Codes were P1545 (Manf control veh spd, Idle spd control, Aux inputs) & P0118 (Engine coolant hi, circuit hi input). I cleared the codes and P1545 came back right away. Cleared it again and no additional codes are showing. Initially the car would not idle, now it idles ok, but low. It will drive, but the throttle is inconsistent. HELP!!

 

try unplugging the MAF and see if the car runs better. I'd also replace your coolant temp sensor, its a cheap and easy fix, you might as well.

 

Thanks; I will try unplugging the MAF today. The P1545 code returned last night after I cleared the codes.

 

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.