the check engine light comes and goes on my 98 a4. the history shows codes p0501 and p1127. car runs very rough first start in the morning. sometime very rough idle, seems like it wants to stall. sometimes this happens while driving and i give it more gas. 50% of the time however it runs fine and the engine light is not on. what should i check or replace?

 

#1 P0501 (Vehicle Speed Sensor "A" Range Performance) probably needs new sensor.
#2 P1127 (Bank 1, Mixture adaption too rich) Lots of potential problems, plugged air filter, bad MAF sensor, fuel injector problems that i would have checked by a mechanic.

 

P1127 is probably thre reason for running like crap.. It means youre running rich. I would check for a boost leak ifyou have a 1.8t. Your MAF sensor might be shot too. Please tell us your engine type when asking tech questions.