93 gsr power loss

I have a 93 gsr(1.7vtec) with 165k. It runs strong 90% of the time but sometimes when im in alot of stop and go traffic, especially when its 85degrees plus, it dosent have much power when i take off or punch it. its not like a typical hesitation. its more like the timing suddenly gets retarded. it goes away once i get going.(i guess something to do with cooling due to more airflow) but once i come to a stop for a long time it will do it again. Sometimes worse then others. And temperature definitely is a factor.It runs perfect when its like 70 degrees and under. My friend was saying it could be the knock sensor since that retards timing when theres a problem but im not getting a check engine light. So i figure the knock sensor is working properly but somthing is setting it off. The cooling system is all good and it runs at the correct temp. I'd appreciate it if anyone has any ideas . thanks by the way, so far ive changed the plugs, wires, thermostat, fuel filter, and tried a couple of diferent fuel system cleaners.

try starting with a tuneup (plugs, wires, etc)