P0016 Code

I did an engine flush this morning and reset the check engine. The car feels like it drives better. After 10 minutes drive the code came back.

The car drives so much better now that I did the flush. Where can I locate this valve to replace or to clean it. I went to a shop and they said it's the cam shaft gears, they want $2k to fix. Is there anything else you would recommend.

I have a 2003 Camry LE w. 1MZ-FE, V-6.
It has 97k miles.
I changed the timing belt, FYI both Haynes & Chilton manuals show the incorrect TB tensioner, and now the MIL is lit. I used a Inovva Model 3030 tester and recieved codes of P0016 & P0018. Actually 4 codes of two occurances of each. I cleared the codes and the MIL came on at start up.
Both repair books indicates the code P0016 is a "coolant temp sensor range or performance."
P0018 is not listed. Also, niether code was in the manual for the tester.
Some web sites indicate the p0016 codes correspond to "crankshaft position - camsshaft position correlation( bank 1 sensor A) & p0018 the same for bank 2.
Is there any way to check without removing the timing covers etc?
Also, the crank & both cams were in correct position according to all marks on all foru( both block & timing marks for crank) at assymbly.
The car runs fine.
Please help.
Thanks, bdl
PS: Dealer said these codes were not in their book.