I have a 04 grand jeep cherokee 4.0L with a few issues going on. Most importantly, there is an odd smell somewhat like sulfur/plastic coming into the cabin. It just appeared but prior to this I removed the throttle body in order to replace the TPS and clean after check engine light prompted me to do so. The engine light did go out and shortly after the smell appeared. Also, oddly my a/c and heater intermittently only works on defrost. I suspect a vacuum leak, but did not see one upon visual inspection of hoses. Are these problems in anyway related to each other?