I have 2000 RX300 that I have been chasing codes with. It has 226K miles. Have replaced cat converters, fuel pump and filters, VVT units, both and have new coils and plugs. Lexus dealer replaced crank and cam sensors. Replaced timing belt, idlers and cam/crank seals. All OEM parts, no aftermarket component. It starts and then after 2 to 3 minutes it throws P0300, P0302, P0304,P0306, P0171, P0171,P01346, and P01356 codes and starts running rough. It has a exhaust pipe leak at the mid pipe in front of the 02 sensor at the hanger location. When I clear the codes it stops running rough and smooths out. I am beginning to think it is an ECU issue. Any suggestions would be appreciated.

 

Please be more descriptive in selecting the title as it would help other readers.

Try this link
Salim

 

Thanks for the prompt response. Will be more descriptive in my titling in the future. The video is informative; my plugs and coils are new, less than 10 miles on them, so will look at other things the guy said in the video.

 

Please can we get some more details and history on your repairs.

Were all these parts replaced because of the codes you listed or are these codes something new?
Any other details- rich fuel smell, clouds of smoke when starting cold, etc- anything that doesnt look or sound normal?
Also, if you have a vacuum gauge and can post video or let us know how your engine vacuum looks when engine is cold and when warmed up and if needle is steady at idle?

 

Hello, thanks for your assistance. I started to get misfire and cam sensor codes in May of 2019. I took it to the Lexus Dealer and they had it for 3 weeks before telling me that they only found low voltage on the cam and crank sensors so they replaced them. Driving it home (40 miles) the engine light returned and so did the misfire and VVT solenoid codes. They had also recommended that I replace the cam and crank seals for leaks; so I did a timing belt, water pump and idler kit since I was in there. I sat in the garage for about a year, then I started to work on it again. I got the plugs and coils and replaced the cats on bank 1 and bank two and both VVT solenoids. The fuel pump and filter were replaced before I took it to the dealer. There is no smell of gas or is there any smoke out of the exhaust. The dealer told me they checked all the vacuum hoses, however I will put a gauge on it as you suggest and run a smoke test. I got the coils on EBay and I have seen that some of the components they sell can be counterfeit, so I will test them too. It may be a few weeks before I can do the vacuum test and video, but I will be back on when I do. I have a 2002 RX300 too; its got 120K on it, really like these first editions. Thanks for reaching out to me.

 

Before chasing a code, make sure the battery is good and the charging system is working well.

Salim

 

I appreciate your help. I failed to mention that when the dealer found the low voltage in the crank and cam sensors they also told me that the battery and alternator were good but approaching end of life. I replaced them both in July 2019, and ran a test on the charging system which indicated All was good.

 

The more details the better- these are the worst kinds of repairs to diagnose. lol

From the added info it seems electrical- could be something as crazy as a voltage drop to ecu thru a cracked fuse, bad ground, wiring harness, Ebay fake parts, etc, etc. I will have a look at the electrical schematics to see if any of those sensors you already replaced have an intersecting plug/junction where wires are in common when I have time unless someone else chimes in.

To rule out some mechanical issues(ignoring the supposed "low voltage to sensors" for now) and see what we are working with I like the Harbor Freight vacuum gauge for $20- several videos on youtube but here is one.

 

Thanks for the video, it is very helpful. I appreciate everyone’s assistance with the problems I am having. I have some work to do with the gauge and component checks, certainly will get me a long way to learning more about what’s going on. I will post an update once I have run down some of the suggested diagnostics.

 

Cool. If if was in your position and because of all the electrical parts your replaced already I would want to know the engine is mechanically ok using the vacuum gauge to spot any red flags before going any further.

If mechanically ok then I would go back to chasing down electrical.