My friend recently acquired a TBI car that had been sitting for a couple years. We got it running without much work, but after a few minutes of driving it would trip a code (43) and start running like crap(it had obviously backed the timimg down). When we checked the timing we found that it was retarded about 10 degrees, so we advanced it and it ran like a champ.

Now the odd part. . .. We initially left the air filter and housing off and forgot to put it back on. We drove the car around for two days, put 120 miles on it, and it ran great and never tripped a code. Then we put the air filter assembly back on and got a code (43) not 5 minutes later! Before we advanced the timing it would trip the code with or without the air filter, but now it will only set it with the air filter (which is new).

Why would putting the air filter on trip the code (43)? Any help will be greatly appreciated.