Erratic, rough idle: only when @ operating temp

Question

Idle drops 150-200 rpm, then returns to smooth idle, sometimes shudders, seems a little worse in gear w/ brake applied. Very erratic, only consistent thing is never when cold or below operating temp. A little more frequent in cold weather. Only code is p0171 (38 times, getting more frequent: now every 6-20 mi). Replaced:     I m r c, plugs, wires, m a f. Cannot find any vac leaks. HELP!

Answer 1

Use a spray cleaner such as carburetor cleaner or even brake cleaner and spray at the suspected areas, If you are sure of the no vacuum leak , you may have a cylinder valve problem causing the lean condition,