ENG CK light in 89 GTA

I've had the engine check light on for quite some time now. I changed the MAF sensor, the O2 sensor, and reset the computer several times (disconnecting battery). Stays off for a while with each change but eventually comes back on after engine kicks down after startup (about 5 seconds later). Had a friend run code check on it and gave a reading that the intake air temp. was high. Which is the reason for the MAF sensor change. Vehicle is pretty much stock except for an after market performance chip, cat back exhaust (3" pipes), cold air induction kit and an air foil in the air intake of the throttle body. This problem started long after all these changes were made (over a year later). Vehicle has 65k original miles on it, most of which are highway miles (trips to FL and such from NY). One problem I've had since purchasing vehicle from dealer (I'm the original owner) is a large puff of smoke at startup. This stops right away. I think it's a bad valve seal which I never replaced.
If anyone has any ideas as to what my next step should be it would be much appreciated.

Had a friend run code check on it and gave a reading that the intake air temp. was high. Which is the reason for the MAF sensor change.
The MAF sensor has nothing to do with the code for the IAT sensor. The intake air temp sensor is screwed into the plenum from the bottom side about 2/3 of the way to the back. Get an inspection mirror and look under there from the driver side. Make sure the wires aren't cut and that the sensor is plugged in. If it all looks good...replace the sensor. The sensor costs about $7 (it is the same part number as the coolant temp sensor) but you'll need to remove the plenum to change it. Advance auto sells an "upper intake gasket kit" for the TPI engines which will have the upper runner gaskets you'll need to put it all back together.