We are having troubles with our 2003 Chev TB. Changed out the cam shaft sensor and now the diagnostics say that the crank shaft sensor is bad. Will this cause the rpms gage to fluctuate when in idle?

I have seen several engines in these trail blazers do this.It is possible that the crank sensor is bad.I would check connectors very closely.The other issue is an oil pressure problem that affects the variable valve timing and causes false cam and crank sensor codes.Have had to replace more than one engine to fix this.Good luck.I would put a manual oil pressure guage on it and see if oil pressure drops below 20 psi hot.

Ok,. ok?? Hello -- if you have a bad crankshaft sensor -- why don't you just replace it??
It's not that difficult and is readily available at your local parts store,. and yes, it COULD CAUSE rpms to fluctuate,. you will not know until you replace the broken part first...
Best regards
Ck

Most crank sensors work or they don't, A vacuum leak will cause that, also check fuel pressure regulator vac hose for fuel in it.