Have a 1994 Villager that has 230,000 miles. Went to smog it and it failed (high NOx at both 15 and 25mph & had low CO).

Replaced spark plugs, air filter, did oil change, ran a bottle of the the "gurantee to pass" stuff through the tank and took it in again. This time it cut the NOx in about half and it passed at 25mph, but failed at 15mph.

The guy at the smog place said he'd replace the EGR valve next. So I went and got one and pulled off the old one tonight. I didn't put the new one on because the old one didn't look that horrible. It wouldn't be mistaken for new, but the "airways" seem to be free from clogs, though they are black with carbon. Should I go ahead and replace the EGR valve or is there a way I can check it now that I've got it off?

There is no check engine light on the van so I'm not sure where to go from here? Should I replace EGR valve, the CAT, O2 sensors? I'd really prefer to do the work myself, but if I have to I"ll break down and take it in.

Thanks for any help!

I had that problem on my 94 when it had 180,000 miles. As I had never put a dime into it, I had to end up getting the engine cleaned out, hoses replaced, and a whole new exhaust system. $3,000 later it passed like new. I have been told that some garages can run something through your engine to clean out the buildup in it, or if going over the counter try the techron stuff from chevron. I think the the bad hose in mine caused it run rich and that's what caused the build-up.