98 accord P0300, P0302, P0304, P1399 cylinder misfire

[vbrhonda98]

I just had a mechanic change a noisy water pump and the tension adjuster on the timing belt (relatively new) which had jumped, and re-timed the belt on my 1998 Honda Accord EX V6. It idles very rough now and the CEL light came on. OBD codes are P0300, P0302, P0304, P1399. What could be the problem? Could the timing belt have jumped again causing this misfire? I am going to do the usual spark plug checks and so on, but can't help thinking something is wrong with the belt. Any insight into this will be appreciated.