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erratic idle when cold

2K views 1 reply 2 participants last post by  505drake 
#1 ·
I have a 99 gmc sierra 1500 4.8L that has a rough idle that jumps from 500 to 1000 rpms and keeps going back and forth until the engine warms up. Other than this issue, the truck runs great. I have no check engine light/ codes. I have read other posts and thusly replaced MAF sensor, visually checked for vacuum leaks, replaced fuel filter, checked coolant temp sensor readings and air temp reading with a scanner and they seem to be normal, and checked fuel pressure. Engine off, my fuel pressure is 50 psi, and running is 52 psi. that seems low, but im not sure. The truck has a new fuel pump that's only 6 mnths old, and a full tune up was done a month ago. This problem is very specific to cold days below 45 degrees, and only occurs when the engine is cold. I have sprayed carb cleaner around intake, and any other suspect areas where I think a vacuum leak could be occurring. Any suggestions on where to go next would be great. Thanks. If more technical info would be helpful, I can get specific reading or whatever u need. kinda frustrated at this point.
 
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