Just checked the codes after searching and I got the "12 42" code. Any suggestions?
1242 is for the air inlet door. If it's a stored code, then it's probably not really a problem. When you press the fresh air/recycle button does the airflow change? If so, then the air inlet door is working. In any event, it's not related to the no heat issue.
No heat at idle could be a failed aux pump.
No heat at anytime could be -
1. Air in the cooling system. On gen I that is usually due to a cracked degas tank. (They crack just as much on gen II, but gen II has other parts that crack a lot too.)
2. The filter screen in the upper radiator hose where it tees off to the DCCV is clogged.
3. The DCCV is clogged or stuck closed.
4. The cold-air bypass door is stuck at the bypass position (you should have gotten a fault code for this).
Warm the engine up and turn the climate control to 90. Wait a minute and then check the three heater hoses near the firewall. If they are really hot, then it might be the bypass door. If they are cool or barely warm, then it's 1, 2, or 3 above.
