When I turn on the faucet, the water comes on normally at first. As I turn on the water further, the water decreases, then increases again. Any idea why this would happen?



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only one faucet or all faucets?

Only the hot and cold taps on that faucet do this. No other sink experiences this phenomenon.

the fact that both hot and cold do this means to me that the cartridges are OK.
i think i would start with the simplest common part... the aerator on the end of the spout.
i'm sure it is something simple. it will just take some trial and error work.

I pulled out the aerator. The water does the same thing. Could both stems be missing a part?



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highly unlikely.

Just to be clear, you have a hot valve and a cold valve on a sink, and both of them are exhibiting this odd behavior? Or do you have a single valve that controls hot and cold?

There are two separate knobs.

Kitchen faucet or lavatory faucet? If kitchen, is there a spray hose, separate from the spout?

Bathroom faucet

I finally just changed the stems. Both were a mess.



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When you said "Both were a mess" do you mean defective or filled with dirt/junk or ?

Neither stem easily came out. One came out broken. The rubber parts came out ripped. I may have caused some of the harm ripping them out. Luckily i had replacements. I really should change my faucets to ceramic disk type valves.