1997 Hilux 5L - Zero intake valve clearance

Hey all, I was hoping for some advice. I have a 1997 Hilux LN147R with the
5L engine, naturally aspirated. I've been having problems blowing black
smoke under load. After replacing air filter, my next port of call was installing
fresh injectors. When removing the throttle body housing to get to the
injectors, I noticed it was full of black crap. Anyway, whilst I was in there, I
decided to check my valve clearances (bucket and shim type). My exhaust
valves were a little tight and out of spec, but all of my intake valves are so
tight I can't get my 0.03mm feeler under there! My question is this, could the
tight intake valve, cause it to be slightly open during combustion and gasses
blowing up into the valve cover, through the breather and into the throttle
body? Also, should I pull the shims and get them back into spec or is it likely
i'd need a valve job. What would you guys do in this situation?

Many thanks in advance,
J