2GM20F Starting?

[hindsight]

Try manually turning engine when cold & then hot if there is a noticable difference in lower compression when cold then remove the rocker cover (cold engine) & when each valve closes make sure the rocker arm is not hard on top of valve causing it not to seal creating loss of compression & that there is some slight play. If not adjust valve clearances & yes if this is the fault it will still start & run ok but will not rev as high.

[hindsight]

If you find manually turning engine when cold is noticeably easier than after it,s been running then remove rocker cover & make sure that when each valve closes the rocker arm is not hard on top of valve therefore preventing it from fully sealing & causing loss of compression, if so then adjust valve clearances & yes it will still start & run ok with this fault but will not rev as high

[TropicCat]

Although I agree that an air leak causes hard starting, it also makes for a rough running engine. .... So...This will make the third answer suggesting you adjust the valves. This is a real easy procedure, will only cost the price of a valve cover gasket and you'll be done in 10 minutes.