1998 Nissan Altima error codes

Car has been stalling out. Took to mechanic, said prob was ignition relay. Replaced distributor Still stalling running even rougher. Also seems to be Having probs at 2000 rpm. Engine runs smooth above or below 2000 rpm. Did the self diagnostic test and got the error code "21, 34" or 2 long 1 short, and the 3 long 4 short. Disconnect battry for 24 hours to clear codes. Started car back up same result, checked the diagnostic, also same result. Looked up codes in the haynes and cant find any to match. M I reading the code wrong or is there something else I am missing?