Recently got a 99 Honda Civic,
It seem to drive fine and the air even worked, but on the way home the check engine light can on with code p0420 (catalyst system efficiency below threshold BK1), Since I had basic 90 warranty from carsprotectionplus . com I figured I wait and see what else went wrong. (I think none of this is covered though)
Then about 2 weeks latter, I notice smoke coming out of the hood on the way to work, and pulled over but couldn't find the from where. It was few blocks to work so I drove the rest of the way and smoke started again, this time I found the hole in coolant reserve. After work, I noticed it was running hot and tried turning on the heater but only got cold air. I drove it home stopping to let it cold down. Now I'm back driving my old chevy since I hadn't sold it yet.

I checked over weekend discovered the coolant reserve had 2 wholes in cap, no straw attached to cap inside, and had coolant above the max near the cap, and little black particles in the coolant.
I also found there was no air filter. (have no Idea why previous owner would remove the air filter, but I'm thinking the P0420 is due to dirty MAS flow?)
Now there were codes p0303 and p0304 (misfire on cylinder 3 & 4 which may have been caused by the running hot?)

I'm curious as to what else I should expect to go wrong, what other damage may have been caused, as well as, thoughts on what the symptoms and codes could mean, and of course solutions.

 

Fix the air filter, clean the maf sensor, get a new reserve tank straw, check spark plugs and wires

 

If you got the car for almost free then try to repair it, but if you got 90 days to return it, I would return it. That car has abuse written all over it. That black stuff could be the radiator was leaking and they put that stop leak in there. Bad CAT alone is not worth keeping. With overflow reservoir could mean they put in too much or you have a bad thermostat shunting coolant back into the reservoir. What's the temp gauge looks like with warmed up and ac running?

 

A MAF on a 99 Civic- really? Please do show - tell us how you have done this before on this car........

Does your 6th gen have a MAF?

 

Air sensor

 

Still waiting on the answer

Take a pic of this "maf" sensor