Chrysler Repair: 3.3L dodge, dodge grand caravan, egr valve

Question
I have a 1996 dodge grand caravan se it has the 3.3l v6. While i was stopped at a red light my van stalled but it was running fine prior to that, when i restarted it as i drove the engine light started flashing and it started running really bad as if it were down to 2 cylenders, i had to floor it for it to move and it was also making a loud clicking noise as the rpm got up. I sacnned the engine code and it came up with 1297(manifold pressure changes) and also (misfire detected in cylender 3). I talked to a mechanic and he said 1297 is the map sensor. I changed but no luck and then it came up with a new code (random/multiple cylender misfire) once it warms up it starts blowing LOTS of black smoke and they smell is so strong it burns your eyes. It also said after i changed the map that there was no 5volt supply to map. And also when i was changing the map both the bolts snapped off in the intake so i am trying to take the plenum off but it seems like it is stuck on something, I removed 4 bolts on front and alt bracket, throttle body. Is there anything on back holding it. Thanks in advance
P.s. When i took it in 2 weeks earlier to have a ticking noise checked out they told me it needs new heads. Thnks

Answer
Hi Rob,
I haven't worked on that engine but the manual shows there to be a strut bolted at either end to the plenum and the cylinder head that has to be unbolted to release the plenum. It appears to be on the rear (firewall) side of the engine near the charge temp sensor and egr valve. That might be why you can't get it off. The removal of the plenum is a multistep process so it would help also if you had the Haynes manual for your van (#30011).
On the other issues, if you can give me the fault code numbers that you last found to be present that may help me to give you advice on remediation.
Roland