The data sheet says 4.7uf?
I might be looking at the wrong datasheet; it says TSOP2138 is discontinued and replaced by another part but isn't clear what that part is (says "TSOP21..."). Anywho, just try something. What I did is set up a little circuit with a transistor to blink a LED when the output pin showed high and then adjusted values until it blinked the least. I really only had problems with the blinkiness when it was in direct sunlight.
I don't think you can use the output of that receiver raw, its just the demodulated signal. The microcontroller should be looking for valid code patterns from that pin. What IR transmitter are you using?
Even with an encoded a message over that modulated frequency the receiver will screw things up if its frequently showing active signals at random.