Hi, My '93 4.3 W with 256k only gets a 45 code (rich exhaust) on the highway after a few hours of driving. The gas milage goes down to 18 or less from 20+. When I stop, even with no code, the engine idols very rough, has a strong exhaust smell and is hard to start. The thing is, after I arrive, it gets better. After a few days its back to 'normal', still idles a bit rough, but decent. No engine light when driving around town. The temp gauge stays around the '1/4' mark. The oil pressure gauge stays at "12 o'clock". I sometimes get blue smoke at startup but not always. Changed the air filter, PVC hose to air filter housing, distributor cap and rotor. The PVC valve, EGR valve and vacuum seem OK. No gas smell near the engine. Could it be the oxygen sensor? Can I clean it? I only have one in the exhaust pipe before the CAT. This van was made in Canada and it seems to like cold and damp weather best. I travel between New York City and Florida every other month, and the last time we made the trip, the engine light was on and off almost the whole way, mostly on. It would go off sometimes when we slowed down for an exit and stayed off for 15 minutes to an hour after we got back on the highway. I don't want to sink too much money into this vehicle but I do like my Astro and would like to keep it going.

they are notorious for having egr problems, had a 96 4.3 that would run horrid because of it. had to clean it out alot. Eventually got a better flowing muffler and it solved the problem.

Rich exhaust is a symptom of an Oxygen sensor going bad. The good part is that a new O2 sensor will pay for itself in gas milage. 256K miles is centainly enough miles for it to be its last legs. My experience, depending on conditions is they can be causing miles per gallon losses in as little as 25K miles but usually they can go twice that. Another point is that a good O2 sensor helps to keep the computer happy and the engine will run better. I just put a new O2 sensor in a Ford pick up and it made a big difference in how it runs. I am surprised how little you hear said about O2 sensors and its not a part that can live forever, considering the enviroment in which it works. (They are in the exhaust pipes before the catalytic converters.)