We were heading back to Auckland from Napier, and I felt the car miss a couple of times, and I thought I saw the rev counter dip a little out of the corner of my eye, but I dismissed it and thought I was seeing things! Soon after it started violently jerking, like the whole car would lurch forward, then seem to misfire. So we nursed it to Taupo and called the AA. He couldn't get his reader thing to read the error codes so he disconnected the battery to reset the computer. He fiddled with the screw on the throttle body, and said that because the computer was responding to him adjusting the screw all the vacuum hoses must be ok. I drove it round the block and it was pretty much back to normal. He thought it was water in the petrol, and advised me to put a bottle of meths in to disperse the water. He said it would help get it through the system and we'd be laughing about it by the time we got to Tokoroa... we weren't. It drove nicely for another 45 mins or so, then started to shudder again. I basically had to drive it home in 3rd as with the revs around 4000 it would still pop and miss a little but nowhere near as violently as when the revs dropped. It would drive perfectly when I put my foot down, but at lower revs and with less throttle it would misfire, shudder, and occasionally add a backfire or two.
After a nervous drive we got it to a mates place in Papakura, then got it towed home as I wasn't willing to risk driving it through Auckland. It had taken multiple starts to get through each set of lights to my mates place.
Now when I start it it sounds like there is air coming from somewhere round the plenum, but it will only run for about 30 seconds before dying so it's hard to check. I checked/pulled off all the hoses off and even removed the plenum to have a look underneath but can't find anything obvious. I don't know where to look now. I wondered if it was a sensor or something, but that wouldn't explain the air leak sound.
I'm at a loss as to where to look next. Any advice would be appreciated.