chuck0080

Im really sorry if this question has been asked before, but i couldn't find anywhere it has. I need some help with my 1994 DOCH Vtech Prelude. I keep failing the hc(ppm) test on low rpm only. At high rpm im running 69 (i need below 220). At the first test my low rpm hc ran at 390. I than replaced the spark plugs, wires, oil change, air filter, and fuel injector cleaner just to see if it needed a good cleaning to get better. This jumped it up to 450 on my next test. I than double checked the spark plug gap, found and fixed a vacume leak through the emissions system, and ran some marvel mystery oil (someone on a different forum said it might help), replaced the o2 sensor and had the cat checked by a mechanic. That got me up to 565 on hc, but only on low rpm. Im at my wits end with this and i can't for the life of me figure out what the problem is. The guy doing the test for me suggested the timing belt was going out becuase on the last test it tested under 220 on low rpm until he took it above 2500 rpm, than tested high again. Does this make any sense to anyone? Or does anyone have an idea of something else i can do. I really apriciate any help i can get with this. Thanks