G'day Guys, Here's the situation... The Car: VE Omega V6 2007 Auto Sedan. Has aftermarket Prins Vapour Injection LPG system. ~326,000km total KM (250,000km on LPG). The Problem - in Brief: Rough idle and diagnosed misfire in no specific cylinder [it changes depending on its mood] ONLY AFTER A VERY COLD START. Resolves itself after approximately 20 minutes of running. The Problem - In Depth: With testing, we've found that the car must have been turned off and in a cold environment [note: we haven't been able to test it in a warm environment (i.e summer)] for at least 10 hours before we can replicate the problem. Upon starting the car, it turns over without any noticeable start problems. The engine then idles at ~1000RPM as it goes through the auto choke warmup phase. After 3-4 minutes after idling at 1000RPM for the warm up, the RPM drops to around 600-700 (as normal). At this point, very small and infrequent misfires are noticeable within seconds. These misfires are mostly also observed on the ScanTool. If the car continues to sit in park and at idle, the misfires and symptoms of a misfire increase in intensity and frequency. I do say symptoms of a misfire because when the car 'jerks', a misfire is not always observed on the ScanTool - however, the majority of the time, the ScanTool does show a misfire. From this point [where the car remains idle], we can completely, but temporarily eliminate the misfiring symptoms in two ways: 1) While in Park or Neutral, Push on the throttle and increase the RPM to 1000 or above. No misfires observed or felt and no abnormalities detected. 2) Chuck the car into gear and go for a drive (Be it Reverse, Drive 1 2 3). While it is under load, the 'misfires' and problems we get while sitting idle are gone. *Note: this does not completely resolve the misfires and symptoms - only letting the car get warm will do that - read on: Now comes the interesting part. After approximately 20 minutes of engine running time, be it sitting idle or under load or both, the next time the car comes to a stop and sits idle (@600-700RPM), the misfire and associated symptoms are completely gone - nothing on ScanTool and nothing felt in the vehicle. It idles without any problems and acts as though nothing ever happened and that it behaves like a car straight out of the holding yard at 0KMH on the Odometer. This will remain the same until it has been shut down and has had a good 10 hours or more rest in the cold (again, can't confirm if it's the same in warmer climates as Winter is really not showing any love). Observations: 1) Symptoms and misfires occur on both ULP and LPG. 2) Once the car is warm enough, by the LPG standard setting in its computer, the LPG automatically takes over - as it should. The misfires and symptoms dramatically increase in frequency and severity. 3) Switching off the LPG and going back to ULP does not eliminate the problem but does reduce the time it takes for the misfires and symptoms to increase in frequency and severity. 4) No reduction in performance observed while car is under load and if it was to go back to idle, the car would still perform the same if I was to push on the accelerator. 5) If it's not clear yet, there is no performance loss while car is under load and does not produce misfires. 6) Misfires and the symptoms of a misfire are only obvious when the car is idle and it's within the first 20 minutes of starting after a rest in the cold for approximately 10 hours or greater (just to make it clear...) 7) The car performs the same and no misfires registered when it is under load while using both LPG and ULP. 8) I've had 2 Check Engine Lights since the onset of this problem and both self resolved and cleared themselves. They did, however, remain in the Log for the mechanic to see. The error codes on all occasions were misfires in multiple cylinders. 9) The misfires, when observed, do not favour one side of the engine. They are all over and can be multiple and single cylinders that misfire. 10) There has been no abnormalities with what is displayed on the temperature gauge - no indication of any over heating etc. HOWEVER, when the engine temperature gauge shows that the engine is warm [where the gauge needle usually sits after 5-10 minutes of running], we are not considering this as the engine being warm. It takes a good 20 minutes for the engine to become 'warm' and the misfire problem is abolished. 11) I'm taking a great personal interest in this point. During testing, the car sat parked on a nature strip. The car was leaning to one side due to the slant on the nature strip. The passenger side of the vehicle was sitting higher than the drivers side. If I had to guess, the passenger side of the vehicle was some 50cm higher than the drivers side. It sat there for no less than 48 hours. On the next start, it started fine (as usual), went through the 1000RPM warm up over a few minutes. After it was done warming, the RPM dropped (as it usually would after the warmup) and at which point I was convinced that the car became a Soyuz rocket and was about to launch into space. It was shaking like crazy & jerking like never before. Interestingly enough this is the only time I've been able to get a check engine light to come up during this specific cold start problem. The car didn't stall but sure as hell would not accelerate at any great pace. The check engine light appeared to be repeatedly triggered - it was constantly chiming and flashing on and off as if a new error came about. The car would accelerate but would hardly move. In fact, I'm sure that the vehicle moved only because it was jerking so much. I pulled over after taking it for a quick 50meter drive to see if I could test it further. After pulling over, I turned it off, waited 3 minutes and turned it over again. No check engine light and it returned to doing its normal misfire/rough cold start behaviour [fine under load, garbage at idle - 20 minutes later, it's like nothing ever happened]. *I have since not tried to replicate the problem by leaving the car on a lean as I just simply haven't had a chance. I should probably try it again through. The car has since been left level when shut down. 12) ...I think it's safe to say that it's a temperature related issue - but I'm no professional. History: ~10 weeks ago, the car started to what I'd call violently misfiring on all occasions [idle, driving, coasting etc] - throwing codes etc etc - all sudden onset. Took it to my usual mechanic, and he observed the same in Cylinder 6 - all other cylinders were fine. He pulled out the Ignition coil and it was obvious that it was time to change it - it was coated in a solid rust-looking like material. Brand new ignition coil goes in and car runs perfectly again - no problemo's. ~6 weeks after that, I started getting a very minor misfire on all occasions. No engine light, but I could feel the car jerk a little every now and then. Take it to the mechanic and all I know is that all ignition coils, spark plugs, throttle body clean and a general lube/oil service was done. Car runs fine again. Over the next week or so, the car didn't get a chance to rest for more than 7 hours (I do a lot of Km's!) until one day, I finally get to leave the car for more than 12 hours overnight at the misses house. Next morning, get up jump in the car. 3 minutes after the start and the RPM has come down from 1000 and bam, here begins the aforementioned rough idle and misfire. Took it to the mechanic, he observes random misfires. Resets the fuel tune on it and tells me not to use LPG and then report how it pans out. I've now an opportunity to thoroughly test the car as it's not traveling 250km a day (thank god for Holidays!). The strange thing here is that the rough idle on startup has now gone but after about 40 minutes of running, I observe misfiring symptoms (read: 'jerks'). I continued testing and seeing if I can find out what is common. Over the next day or two, it does the same - jerk/ misfires while warm. I get home, leave the car for a good 12 hours overnight and BAMMMM - we're back to the same old cold start rough idle problem and it has been the same ever since. As of yesterday, the Mechanic has tested & replaced ignition coils (again), cleaned the injectors - which were dirty and checked the spark plugs which were recently replaced as part of a normal service (the same time they did the oil etc). His off-sider seems to think it's a sticky valve. It is due to have an idler pulley replacement I'm still running the car and it runs fine - it's only that initial 20 minutes after it resting for 10 hours or greater - but, it is still the same. If anyone has any ideas, I'd love to hear them and share them with the Mechanic. I rely on this car and I know 326,000kmh is old but I'm not going to throw away what appears to be a perfectly good car that is just a grumpy b&*$h when she's cold. Cheers Steve PS: apologies for the long post.