12V pump on idle??

Hey, went camping for the first this year, noticed this problem when we got the trailer last year, but though I figured it out...well I didn't. The Situation went like this...the pump did not get to pressure, it would sit and cycle...yes 12V is at the pump (pump is running). Took the bypass cap off (to winterize) and put a water hose to that...thought maybe it needed primed??? Just put water all over the place, pump did take some water, but not much. Cussed at it, hit it with a hammer--ok tapped it while it was running, tried the water bypass again...no go. DD thought to turn the power off and...she did that 5-6 times.. still no go.

morning time, went to take the pump out (we were going into town anyway) decided to try the pump one more time...it fired up and had pressure...and when it gets to "pressure" it slows down and like idles..cycles really slow..almost like a leak...it had done that when we first got the trailer last year, I thought the diaphragms were dry..PO did not use trailer very much. I let it sit and idle-cycle for a couple of minutes...then it got to pressure and turned off--stopped running. Turned on the furthest faucet and lots of pressure, pump turned on, I turned off the faucet and pump went into the cycle phase....it will cycle for 2-5 minutes and eventually turn off--get to pressure... It will sit at pressure for as long as we don't touch the faucets...so there is no leak in the system....

sorry for the long drawn out story, now, question...has anyone had this problem before???