I have a 1998 Lexus LS 400 that’s developed a strange misfire issue. It comes and goes and it’s always on the driver side of the engine. I can go a couple days where it runs perfectly smooth and quiet and then it will spend the rest of the week misfiring on all 4 driver side cylinders. Sometimes while it’s misfiring it will clear itself up within a few seconds and go away. This only happens at a stop. As soon as you pull away it smooths out again. Although, sometimes if you’re coasting or lightly on the throttle around 40 mph the car will jerk and buck. Interstate driving is smooth as silk. There are also sometimes where it idles at 200 rpm in gear while misfiring. Other times it will idle around 500-600 in gear while it misfires. There doesn’t seem to be a pattern to when it does it. It usually will misfire badly after it warms up but sometimes it will do it when you first start it up in the morning. When it is running rough the exhaust will stink and smell very strong. Not like raw gas but more just a bad odor. It’s hard to describe. Maybe a French fry smell or something. I’ve tried running several tanks of fresh gas through it with fuel system cleaners. That hasn’t worked. I took it to a shop and they gave up trying to diagnose it. It has the random misfire code, individual misfires codes for each cylinder on the driver side and an OCV code. The coils and injectors have all been checked and are working correctly. Any ideas? I’m at a loss. I’ve heard so many theories from a bad computer to bad OCV.
What are the codes?
How many miles on the car?
Has it been sitting for a while?
Has a compressoon test been run?
Have you checked the fuel pressure and injectors?
Have you traced the wiring harnesses for breaks or corroded grounds?
The car has 275,000 miles on it currently. It’s my daily driver. The codes from what I remember are P0300 random misfire code, various codes for misfire on cylinders 1,3,5 and 7, and P1349 code for VVT solenoid. No compression test has been done. The fuel pressure hasn’t been checked but all the injectors were checked and said to be working like they should. I haven’t gotten into the wiring. That’s beyond my level. The shop I took it to didn’t get into it as much as I hoped they will so I’ll probably go somewhere else. Since it is able to run and idle smoothly for days sometimes and then run rough other times I’m doubting it’s a mechanical issue. Probably something electronic. I’m going to try replacing the VVT solenoid and see if that helps anything. What are some other things to look at if that doesn’t help? I’ve had the well known mechanic Scotty Kilmer tell me he thinks it’s a bad ECU.
A car this old with this many miles I’d suspect a wiring issue. Partially broken wire or corroded ground could cause an intermittant problem.
If Scotty is willing to pay for the ECU if it you buy one and it still doesn’t fix the car, go for it. Assuming of course you can still buy one.
Not a mechanic but my gut is telling me the VVT solenoid is largely responsible. If the valve timing for one bank is out of whack that would cause misfiring for the entire bank. @Mustangman also has a good idea, check the wiring for the driver’s side VVT solenoid.
That’s all well and good, but if–as I surmise–his diagnosis was done from afar–via cyberspace–you can’t take that as authoritative, and you need to have a qualified mechanic who can do a hands-on examination and provide his/her diagnosis.
My mother taught me that if I don’t have something nice to say about someone I shouldn’t say anything at all. I’m going to ignore that advice now and say that I’ve heard Scotty Kilmer spout enough idiocy that I wouldn’t trust him if he said 2+2=4. It used to be fun to watch him on youtube just for kicks until I heard him say that you should change your air filter to keep the engine temperature right.
As far as your car, your engine computer is telling you that cylinders 1,3,5,7 are misfiring at times and that there is an issue with the valve timing system. Seems the first thing to do is fix the valve timing issue, probably with a new VVT solenoid.
Can you actually put Scotty Kilmer and mechanic in the same sentence and keep a straight face. 
Even my wife knows better. Once I had him on Youtube as we were making dinner. After a few minutes she asked “is this some sort of blooper reel?”