Chevrolet: 3.4 Ltr. Qestion, fuel pressure guage, maf sensor

Question
What would cause the 3.4 to sometimes not want to idle and then go to a fast idle over 2500 rpm.  We changed the PCV valve which seemed to help temporarily?  

Answer
Could be a number of things. First off I would suggest changing the fuel filter if its been over a year. Then I would change the spark plugs if its been more than 3 yrs. Also clean the screen on your MAF sensor with some sensor safe spray available from any parts store.

If the problem persists, attach a manual fuel pressure guage and check to see if the fuel psi is low or surging at idle.