I have 2004 chev trailblazer, 4.2 L and check engine light on constantly. I brought to mech & he got a code 4 the air pump cct. (not sure code #) He said all he could do with it was check the relay & it checked ok! I would have to bring it to a dealer. Also when its cold it idles's poorly sometimes stalling or reving to high @ stoplights. Could these 2 problems be related? Any advice would be appreciated.