Driver School Candidate
Join Date: Jul 2007
Location: New York
Same experience & some insight...
Crystal et al,
I own a 2006 Lexus IS 250. I'm a pretty well experienced and well equipped mechanic, and my wife drives the car daily. The vehicle now has 130,000 miles on it, and aside from this issue, the car has been excellent by any measure.
When the vehicle had 5,000 miles on it, we were driving down the freeway, and the SEL started flashing, and it was obviously running on 5 out of 6 cylinders. I pulled over, turned the car off, restarted, and all was fine with the service engine light (SEL) illuminated. I drove to my shop, plugged it into the computer, and it was P0306 - Cylinder #6 misfire. I scheduled an appointment at the dealer the following day. They pulled the same code, swapped coils and gave it back to me. That's reasonable, and probably just what I would have done. This happened every few months at 15k, 22k, 38k, 55k, 65k, 85k, 115k, 125k, and a whole lot lately. When it was under warranty, it went in every single time to document the problem, and they couldnt' reproduce it. The misfire was stored, but it wouldnt' happen again for months. After it got out of warranty, I brought it to the dealer at 85k, and atain at 126k. I can tell you that it's not necessarily 1 culprit cylinder, it moves around, but mostly #4 and #6, the two rear-most cylinders. Switching coil packs does not identify a particular coil pack that's causing the problem. While in the beginning, pulling over, turning the car off and turning it back on solved the problem, in the last year or so, it's taking multiple restarts to get the car going again, and lately, it's been more and more. Just today, my wife was stranded on the side of the road, and is getting towed as we speak. Restarts will not solve the problem.
One time around 90k, it acually happened when I happened to have a OTC Genesis diagnostic computer sitting in the trunk. i pulled over, and plugged it in while the car was still running on 7 cylinders on the side of the road, and I could see the misfires climing constanly consistent with a dead cylinder and the stumbling feeling. Fuel pressure looked good, and none of the other values stood out as a potential cause. I turned it off and on again, and all was fine.
As for theories...
The fact that a restart solved the problem, that would SEEMS to indicate an ECM related issue, either with one of its sensor inputs or with the software itself. It is, however only a guess. Something changes before and after the restart. P030X is a performance DTC, so it's not a matter of a sensor indicating a value out of range, so it's not as simple as easily diagnosing a bad sensor.
I don't have updated valve springs, however I have heard of others having their springs changed with redesigned springs. I'm not sure if they had 350's or not, but I have seen them on the boards. The dealer has not suggested this, so I assume it's not a factor. There is a TSB released in the last year about flawed rings causing issues like this, and the fix is new pistons and rings, and if the block is scored, a new block. In a case like that, the most cost effective option is to put a used motor in the car, which I'm prepared to do myself, if someone can tell me that's the case, but they can't. Motors go for around 2k, and I can accomplish the swap myself, but if the cause is electronic, then that's a lot of money for nothing. I'm not about to guess.
When it was out of warranty, I brought it to the dealer because I felt that the best use of resources was to take advantage of a shop who would have likely seen an issue like this before and solved it., but that does not seem to be the case, and they claim they haven't seen an issue like this ini the past. Tons of misfires cured by a top engine clean or induction service to remove carbon from valves found to cause low compression is very common with this motor, however I have performed several top engine clean procedures and induction service, and have pretty much ruled out carbon buildup. Any misfire MUST be caused by one of three things - fuel, ignition, or compression. Today, it's happening constantly for the first time, so I'm going to attempt to plug the computer into it, identify the cylinder and check fuel pressure (which the computer can easily tell me) and compression in the dead cylinder. If there is low compression, I can tear the motor down and figure out why. If there is plenty of compression, then I would attempt to identify whether or not the plug is firing, but I'm not yet sure how.
The worst part of this is that if you drive it was a dead cylinder, then it may be dumping fuel into the exhaust, which will shortly destroy the catalytic convertors, which are extremely expensive.
This is a mystery, and I have been trying in earnest to troubleshoot this for years to no avail. In defense of the techs at the dealer, there isn't much to go on without tearing the motor apart, and that's obviously tough to justify at this point. It has been happening since the car was brand new, so whatever the issue, it's been pretty consistent throughout the life of the car, only it's difficult to reproduce, and can be weeks or months between occurrances. Until recently, it wasn't a deal breaker as at most a few restarts were all that was required to remedy, however now that my wife is stranded, the calculus has definitely changed.
Hopefully, this will happen consistently, which should aid in troubleshooting. It sounds as if the issues are very similar.
Michael D. Bailey