Obviously these are not allowed for runs. Use them to explore the game! Feel free to post your own.

If one code doesn't work, try the other code.

PEKNAYLE / PAXNAYLE Play with 9 lives GXSZZVVK / GZNXGVVK Infinite lives GEKYSZZA / GAXYSZZA Qualify every race! PEUYXZLA / PAOYXZLA Ruff Trux after every race PASYNALA / PEUYYYLA Kid out of game after every race GEKNIYAA / GAXNIYAA Start on race 5 PEKNIYAE / PAXNIYAE Start on race 10 TEKNIYAE / TAXNIYAE Start on race 15 LOKNIYAA / LPXNIYAA Start on race 20 AOKNIYAE / APXNIYAE Start on race 25 (Final Race!) GESYOZPA / GAUYOZPA Win Championship race! AAOEIAIA Faster Boat acceleration AAOEGAIA Faster Sports Car acceleration AAOETAIA Faster Formula 1 acceleration AAOEYAIA Faster Turbo Wheels(tm) acceleration AAXAAAIA Faster 4x4 acceleration AAXAZAZA Faster Tank acceleration AAXALAIA Faster Chopper acceleration AAXATEPA Quicker Boat deceleration AAXAIEPA Quicker Sports Car deceleration AAXAYEPA Quicker Formula 1 deceleration AAXEAEPA Quicker Turbo Wheels deceleration AAXEPEPA Quicker 4x4 deceleration AAXELAZA Quicker Tank deceleration AAXEGEYA Quicker Chopper deceleration YAEAZAPA Higher bounce for Boats IAEAPAPA Higher bounce for Sports cars YAEALAPA Higher bounce for Formula 1's YAEAGAPA Higher bounce for Turbo Wheels YAEAIAPA Higher bounce for 4x4's YAEAYAPA Higher bounce for Tanks

Source: https://www.gamegenie.com/cheats/gamegenie/nes/micro_machines.html