Here are my results:
Yes, the upper intake plenum needs to be removed. There are six bolts that hold the upper plenum to the lower. Those are very easy to remove. There are also two brackets with bolts, one on the right side and one against the firewall, that need to be removed. Before you remove the bolts you have to remove everything from the plenum. The EGR valve, intake tube, a bunch of vacuum hoses, wires, etc. I removed the cruise control on the upper left side of the engine compartment to gain more room to reach the back of the plenum. After everything is off you can pull the upper plenum off the lower. Pull it up and forward a bit so you can disconnect the two vacuum lines that attach to the back of the plenum. After that it will be free to come out. Once that is done changing the plugs and coil packs is very easy.
Reassembly is fairly easy but the vacuum lines under the throttle body can be tricky to oraganize. Take your time and you will figure it out. I reused all the gaskets and so far no leaks.
I did find another major problem once I remove the plenum. The large vacuum hose that connects to the back of the plenum had collapsed, melted and had two holes in it! I picked up a new hose from a local Mazda dealer. They informed me that that hose is a known problem with the MPV. The new hose is much thicker and stronger where the previous one had failed.
Anyway, the car now runs better than it ever has according to my friend. I assume the misfire problem was probably caused by the blown vacuum line not the coil packs/plugs. We still changed them since we already had everything apart.
Saturday, November 3rd, 2018 AT 8:02 AM