1994 E420 Help

[4wheeling]

Hi,

I have a E420 with 128000 miles the check engine light keeps coming on and off. When on it stayed on for a while and when off stayed off for a while. Lately it is on and wont turn off. Using the push buttons I read code 4 something to do with air injection. The air pump seems to work ie. it comes on when cold and shuts off after a while. What is code 4 and how do I diagnose this problem. I have the home built code reader too so probing pins would be no problem.

The second problem is with the climate control. The ac works fine. Just recently it started to get cold and temps dipped into the low 50's. When I set the interior temperature to 75 and set fan speed to auto the air that comes from the vents is not warm at all even after the car warms up. I don't know if it is related but one thing I noticed is that on a hot day (90+) when the ac is on and the car idles a lot (30 min +) occasionally the side vents blow hot air in. It keeps blowing for a while and then switch back to normal.

Thank you.