ALTDEV EXCURSION FROM ASSIGNED DUE TO EVASIVE ACTION DSCNT TO AVOID VFR XING TFC. LOTS OF UNKNOWN VFR TFC IN AREA.

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ON A RECENT IFR FLT PLAN FLT IN VFR CONDITIONS; I WAS BEING VECTORED TO THE FINAL APCH COURSE FOR LVK AND WAS ADVISED TO MAINTAIN 3300 TO FOOTO INTXN. MY SAFETY PLT COULD SEE A LOT OF VFR TFC IN THE AREA AND AT ABOUT 8 NM E OF THE TCY ARPT; I DSNDED TO 2800 TO AVOID A POTENTIAL CONFLICT. THE PROB IS THAT I DID NOT NOTIFY APCH OF MY INTENTIONS AND THE ALREADY BUSY CTLR ASKED IF I WAS INITIATING THE DSCNT EARLY; MISTAKING TCY FOR LVK. TO COMPLICATE MATTERS; I REMOVED MY HOOD AND SAW THE ARPT'S RWY 25 DIRECTLY IN FRONT AND BELOW! FOR A 'SPLIT-SECOND' (MENTAL TRANSITION TO VFR); I LOST TRACK OF FOOTO INTXN AND; IN A HURRIED RESPONSE TO THE CTLR'S QUERY; REPLIED; 'I MUST HAVE' (CONFUSED TCY WITH LVK). IT TOOK A FEW MORE SECONDS TO VERIFY FOOTO ON #2 NAV AND I TOLD THE CTLR WE WERE CLBING BACK TO 3300 -- BUT WITHOUT EXPLANATION. A SHORT TIME LATER; THE CTLR HAD TO VECTOR US AROUND ANOTHER CONFLICTING VFR ACFT MANEUVERING THROUGH OUR FLT PATH. WITH THIS OUT OF THE WAY; WE RETURNED TO COURSE AND COMPETED AN ILS APCH TO LVK. LESSON LEARNED -- IT IS MORE DIFFICULT TO FLY IFR IN CROWDED VFR CONDITIONS; TRYING TO SEE AND AVOID (CTLR ADVISED AND NOT ADVISED) TFC AND COMPLY WITH IFR RESPONSIBILITIES. CERTAINLY; WE SHOULD HAVE TOLD THE CTLR THE REASON FOR OUR ALTDEV WHEN TIME PERMITTED.