Chevrolet Repair: truck idle falls down to about 200/250 rpmafter it is started, throttle position sensor, throttle plate

Question
my 2002 4x4 silverradlo 6.0 engine won 't after it is running.I had a new air idle control valve installed. I had the throttle body clean,no computer codes, fuel pressure is 48 should be 52.a friend said that might be the prolem

Answer
HI JIM, 48#'s OF FUEL PRESSURE IS OK. THIS WILL NOT CAUSE A LOW IDLE. LOW FUEL PRESSURE WHICH THIS IS NOT, WOULD CAUSE NO TO LOW POWER ON THE OPEN ROAD,VERY LOW PRESS WILL CAUSE A STALL OR NO START AT ALL. I WILL ASSUME THAT THE ENGINE RUNS STRONG OTHER THEN LOW IDLE CORRECT !!! I AM GOING WITH THIS. YOU SAY YOU HAD THE THROTTLE BODY CLEANED. DID YOU CLEAN THIS ??? IF SO DID YOU CLEAN THE FRONT SIDE OF THE THROTTLE PLATE OR THE BACK SIDE OF THE PLATE ???? FRONT SIDE DOES NOT MATTER. THE [MOST] COMMON PROBLEM WITH THIS ENG WITH LOW IDLE IS THE BACK SIDE OF THE THROTTLE PLATE FILLS UP WITH CARBON. OPEN THE THROTTLE ALL THE WAY AND GET SOME CARB CLEANER AND A RAG AND TOOTH BRUSH AND CLEAN EVERY SPOT OF THE BACK SIDE OF THIS PLATE. DO NOT USE ANYTHING ABRESIVE ON THE PLATE...I HAVE CLEANED MANY,MANY OF THESE 6.0 LIT'S FOR THIS AND IT USUALLY TAKES CARE OF IT...SO, LETS SAY YOU DID CLEAN THE BACK SIDE OF THIS PLATE, NOW THIS GETS TRICKY. I HAVE SEEN BAD TPS THAT WILL CAUSE THIS. [THROTTLE POSITION SENSOR]BUT NOW YOU WILL NEED TO GET A SCAN TOOL TO RUN SOME DATA INFO TO SEE WHAT IS GOING ON..DO NOT WASTE MONEY ON THROWING PARTS AT IT. TAKE IT TO A SHOP WHERE THEY CAN SCAN THIS FOR DATA, NOT TROUBLE CODES..THIS WILL BE CHEAPER IN THE LONG RUN. LET ME KNOW IF YOU NEED MORE INFO ON THIS. PLEASE WHEN YOU LEAVE THIS SITE WOULD YOU MIND RATING MY ANSWER. THIS WILL HELP ME. THANK YOU, TOM..