Spraying TB cleaner into the intake will only remove some surface coating and you might have a heavier buildup requiring removal & cleaning of the intake manifolds. (maybe?) Driving without the gas cap wont cause any damage although it may set a CEL which should go away once the cap is replaced. The TB cleaner should not hurt anything and/or cause future CELs. To know if your CEL has anything to do with a dirty intake, you should get the code "scanned" from the PCM computer. Autozone and other part stores will frequently do this for free. Post your codes and let us know what engine, trans, mileage, and mods you have on your car. The codes are also listed here:
http://contour.org/FAQ/FAQ.cgi?s=probs&display=checkengine
