What was found
AT APPROX. 2000' AGL WITH ENGINE ANTI ICE ON AND AT FLIGHT IDLE. BOTH COWL VALVE LIGHTS ILLUMINATED MOMENTARILY AND BOTH DUCT PRESSURE NEEDLES STARTED FLUCTUATING BETWEEN 20-60 PSI WITH POWER UP WHEN CONFIGURED FOR LANDING. DUCT PRESSURE FLUCTUATION SETTLE BACK TO NORMAL. GROUNDED - YES. PERFORMED B737-9 IFIM TASK 30-21-00-810-807 ENG #1 COWL LIGHT VALVE ON. FOUND NO MAINTENANCE MESSAGES CHAP 36 PNEUMATICS, NO MAINT MESSAGES OR EXISTING FAULTS FOUND.