I have been working this for a week now and am completely stumped. Help!!
Our 2004 RR started missing severely and pretty much out of the blue. It is most noticeable when sitting at idle with the transmission in gear, and also when just starting out from a dead stop. It is not bad enough to change the RPM indication when tranny is in park/neutral, but you can hear it in the exhaust. The check engine light does NOT come on unless we accelerate at full throttle, and then it merely flashes and goes out when we back off the throttle.
Here are the diagnostics info:
1). Incident first happened after filling tank. Ran the testbook and the only code is “misfire cylinder 7”. I replaced the ignition coil and spark plug on #7, and cleared the code. There was no change in the misfire. Diagnostics now said “misfire cylinder 2”.
2). At this point, I had to assume I got bad gas, since the misfire was moving from cylinder to cylinder. I called the station, who of course denied any other incidents. Also, we filled our other car at the same pump at the same time...and that one has no issues with the gas. Still, we added Heat gas treatment, ran the tank to the low light and then topped off with good gas, just to be sure.
3). As the tank burned down, the missing slowly got better, but never completely went away. On filling the tank with fresh premium gas, the missing got severe again.
4). At this point we pulled the codes again: “Misfire cylinder 2”. “Multiple cylinder misfire”. But 2 new codes appeared...”DM-TL small leak 1.0mm”, and “fuel system pressure test fail”.
I am stumped. The missing does seem to be related to the amount of fuel in the tank, i.e. full tank worse and low tank better. But I have never known the evap side to cause missing. Does anyone have an idea of where to go from here?