Hi Jeff, I have had this on numerous vehicles I had to drive a Renault just a couple of miles to the garage with a misfire on a cold & dark winters evening, when I got into the workshop I thought the car was on fire as an Erie red glow came from under the car. The whole exhaust was so hot from front to rear I thought it was going to melt onto the floor. Any Cat vehicle with a misfire allows unburnt fuel & excess oxygen into the Cat which flares off the fuel in the Cat raising the temperature to extreme temperatures. I am almost willing to put money on the fact that one of the coil packs has gone down, causing the misfire, these coils are so prone to problems. A misfire will seriously reduce vacuum making you think there are other problems in the system. HTH John Kennard.