Almost immediately after starting the engine, I get a exhaust odor coming through the vents. When the car is moving it seems to go away. When idling, it seems to come back though by this time it's hard to really tell.

I did have a check engine light a while ago that suggestd I replace my downstream O2 sensor. So I did, and haven't had a check engine light since.

I changed the oil, installed new, properly gapped spark plugs, and air filter. Still there. Is there somewhere obvious I should be looking?

I do have an OBD-II reader that attaches to my laptop so I can read the realtime values of the O2 sensors, if that helps any. I don't know what the values should be at what time.

Thanks!

 

If it really is exhaust and not something else burning, than I would focus on the exhaust system, starting from manifold back. If you're blowing exhaust out near the outside cabin air intake, that'll be your problem. When you start moving, there is more fresh air coming over the car, and once the exhaust warms up and expands a little, it may be sealing it off, explaining why it doesn't come back at say a red light or other stop.

 

Yes, start at the front and work back, you should be able to hear it, but sometimes you need to use your hand to actually feel where it is coming from. A short length of hose between your ear and the exhaust manifold will keep your hands from getting burnt trying to check that gasket.