What was found
AT SLATS RETRACT, 250KTS .538M, FL 160 THE UPPER FOOT WOULD NOT MOVE UP FROM 258 KTS AND ALLOW THE ACFT TO ACCELERATE, IMMEDIATELY GOT STICK SHAKER, THEN REDEPLOYED THE SLATS. ACFT WAS ON A/P 1 AT TIME OF SLAT RETRACTION, DISCONNECTED AUTOPILOT WHEN STICK SHAKER ACTIVATED AND HAND FLEW. PERFORMED PSEU TARGET TEST FOUND SENSOR NR 1 FAR WHEN IT SHOULD BE NEAR (SLAT EXTENDED). R & R LT WING NR 4 SLAT SENSOR "A" IAW MM 27-84-03-4. OPS TEST OK.