Lexus Troubleshooting Questions? Ask a Lexus Expert
at any time did the check engine light come on or start the Flash? Do you have the ability to be able to pull the spark plugs when it's running rough and you see the smoke and fuel smell from the tailpipe?
I wasn't suggesting that the plugs are the problem what I was suggesting was when it starts running rough and acts like it's burning excessive fuel you would need to shut it off at that point pulled the spark plugs and see if any one cylinder or spark plug is soaked with fuel or covered with carbon. That would give you an idea if there was any particular cylinder or injector that was malfunctioning. Is extremely unusual to see computers fail. It's not likely the timing belt or any of the components because that would not come and go. However there are some sensors and some things that could throw the timing out causing inaccurate fuel injection time and Spark which could be intermittent that would be close or related to the timing belt that is what my thought process would be at this time. Without putting a fuel pressure gauge on it and checking what the fuel pressure is doing when the problem occurs and monitoring the cam sensor and crank sensor inputs to the computer to see if it's erratic would be the only way to test this or to start investigating as to what's going on. I could guide you through some specific tests but before you waste your time doing that if this was never an issue prior to having a timing belt done I would at least have them take a look at the wiring harnesses and things that are close to the sensors on the front cover area. Let me know how you'd like to proceed. It is also not likely sticking injectors.
I can't directly answer your question cuz I don't know whether the dealership you're dealing with has somebody with diagnostic skills and knows how to professionally use an oscilloscope as I do. Unfortunately not all dealers are staffed the same. The capacitors that you referred to are probably the drivers that are bolted to the side of the ECU case. I have seen them overheat and Bubble Up and cause the injectors to spray erratically or not at all. It's worth popping the computer open and taking a look at them but if you don't have the time to do this you need to find a good diagnostic guy that can step by step go through all of the inputs to the computer that could cause extended fuel injection duration or mismanagement of the injection time vs. The spark. All of these inputs should be monitored with the scope I typically pick the top four and put it on a 4-channel scope and monitor it and record it when the problem occurs. This works great with vvt-i systems amd so on
as as I mentioned before I think it would be worth having the dealership that put the timing belt on take a look to see if maybe they didn't get one of the sensors or reluctor wheel for the cam and crankshaft timing. Something is very suspicious if this was never an issue prior to the work that you just had done. You cannot Overlook the basics and the obvious things that they were under the hood playing with.
I'll be around let me know what they say. What part of the country are you in?