Over the last few days, my LS430 has started running rough, and economy has plummeted. Idle speed can vary. Sometimes it will idle very slow, and run very, very rich. Rich enough to smoke. I found a pipe that had come out of the rubber tube connecting it to another pipe, so I joined them back. No change, MAF and Throttle body were cleaned about a couple thousand kilometres ago, as was the air filter. Not that they were dirty, they weren't, but just general maintenance. I was on about 1/4 tank of fuel, buit have filled it up, so it is most unlikely to be bad fuel. The trans is also not quite as smooth changing as usual, but it wouldn't be noticed by anyone else. The exhaust smells, which I assume is the Cat working hard. I have disconnected the battery for 30 minutes, to reboot the system, then run a 40km or so trip to try and reset the computer. Tried that 3 times! I hjave a HUD plugged into the diagnostic port, and it normally shows the same instant fuel consumption as the dash. However, at the moment it shows a bit higher consumption than the dash. There is no Check Engine light showing.

Any thoughts what else I can try?

Thank you.

 

O2 sensors, maybe?

 

I would look at all the vacuum hoses, maybe one has come loose or cracked. Is there anything clogging the air passage from the intake to the air filter, such as road debris, leaves etc.?

 

Does your scanner read live data? You need to see short and long term fuel trims (stft, ltft) and O2 outputs. Could be lots of things like other vacuum leaks, failing/sticking fuel injector(s), failing fuel pressure regulator, etc.

 

Same experience with my 01 LS 430. No MIL on dashboard. Checked spark plugs, vacuum hoses/lines, ignition coils.
It turned out to be the VVTI valve, was packed with sticky kind Tar of oil (must be improperly maintained by previous owner).
Cleaned it up, and the car runs great again (But need to change that valve after a year.)

 

Thanks for your reply.
I have only just bought a scanner today, so haven't tried it yet. I used injector cleaner about a month or two ago. I imagine there are lots of vacuum hoses scattered throughout the engine bay? Is it possible all this running rich might harm the cats?

 

Howdy. How would one check the VVTI valve? Take the front covers off? What would I look for?

 

HI. No reason why there should be anything blocking it like that, but I will check it. This has happened before, and just a reboot fixed it very nicely, and quickly.

 

I have just bought a scanner today, so hopefully it will work on this car (some appear to not work on Lexus). So it should tell if it's O2 sensors, when I get time to have a look at it.

 

I mean VVTI solenoids, there were two of them
(Left and right bank).
They are right up front adjacent to the upper timing belt cover fastened with a 10 mm bolt, (unplug the elect. connection remove the bolt then pull out the solenoid).
The left side is right behind the air intake tubing and box- need to separate it from the engine air intake filter box to get a good view of the solenoid.
When these solenoids malfunction, it causes a really rough idle, intermittent lean/ rich.
It happened to mine without even throwing a check engine light.

 

Check your PCV Valve and PCV Hose. Also, replace the MAF sensor as cleaning them is just a bandaid and even if they look clean, they most likely aren’t. My 439 was doing the same thing. Replaced those three and problem solved.

 

Replacing ignition coils on my girlfriend's Nissan Versa with 135K miles resolved this exact issue. I also replaced the spark plugs since I was there since you have to take off the intake manifold to do this job on a Versa, but they looked fine.

There were no engine codes but it was evident the Cylinder 4 coil was on its way out and it was showing misfire counts. On Nissans, there's a section on a lot of their coils that effectively melts when the coil is bad. Cylinder 4 was starting to show those signs. She went from consuming almost 1/2 a tank of gas to drive 1.5 hours to just 1/8 of a tank (highway). I filled her up when I was out test driving. She sent me a text of her gas gauge after her drive home (a 1.5 hour drive, she lives that far from me). She filled up before she came to my place and when I started work on the car her tank was only half full. The improved mileage is continuing, as she says, and the engine is running far better in all aspects.

With your new code reader, look at all cylinder misfire counts. If one of the cylinders is counting obviously higher than the rest -- at least change that coil. The fuel in that cylinder is not being burnt (or not being burnt cleanly) and that'll eventually foul your cats and you'll either be replacing the cat on that bank or attempting a high-rev cat clean exercise with a chemical flush of some kind. I used Seafoam to do this on a Toyota Camry that was driven with two bad coils for probably 30K and ran a whole can through the intake vacuum (slowly). It wasn't a fan of breathing in Seafoam, of course, but after letting it sit for 30 minutes I did some high rev accelerations out on the highway and all of a sudden a poof of white/light gray smoke spewed out of the tailpipe and after that it ran like butter for another 100K. That was years ago. Now I would probably opt for a BG product instead of Seafoam but... it worked.

If you don't know what you're doing with chemical cleaning... don't do it. You'll ruin sensors or hydrolock your engine.

The aforementioned PCV valve/hose and MAF clean is a good idea. Be GENTLE with the MAF sensor cleaner. Don't spray the MAF like a firehose. Short bursts. You won't use or need to use the whole can on one MAF sensor.

 

I am now back to normal! There were no codes, so I took it to a mechanic/engineer guy, Richard, who has a professional scanner, still no codes, apart from one for the heater which fault I knew about. The fresh air/recirc flap doesn't work. So we removed the wiring plugs from the VVTI solenoids and applied 12 volts to them to see if they clicked and appeared to work. They did click, so we clicked them on and off a few times to make sure they were clear. Put their plugs back on and started up. Appeared okay. He then said they have a Suzuki Swift that occasionally does similar, so they do that solenoid trick, and all is good. It appears that because the vehicle is only used carefully, never given its full potential, the solenoids are not getting to do any work. Likewise with mine, rarely give it its head.
Anyway, after that I drove home. Everything appeared good. Idle speed, idle fuel consumption, idle smoothness, driving fuel consumption, smooth move off from a standstill, all gear changes as smooth as the proverbial, HUD consumption agreed with the dash readout, instead of reading quite a bit higher.. In short, everything is now great. Exhaust pipe was still black when I got home, but rather less so, but I figured that was probably what was still in the exhaust pipes and mufflers etc, and would probably burn off, That has happened. Now I need to cane it occasionally, give it heaps! Richard, said the oil is cleaner than he's ever seen. I think he thought it must have just been changed. But no, it's done 3500km. That surprised him. So I guess there ain't no wear!
I have previously cleaned the MAF Sensor and throttle body with proper cleaners. One time it appeared to make a slight difference, other times it hasn't, and those times, the MAF always looked clean anyway.
So, thanks everyone for your suggestions, much appreciated.

 

You need to thrash all internal combustion engines every so often. I give mine the beans at least once per trip, even if it's just a 2 mile trip to local stores.
The VVTI solenoid won't switch unless you get to at least 4k Rpm, although the "Intelligent" part of the control may switch it sooner depending on throttle position, speed, load etc.
Glad ya got it sorted though. Now go enjoy the upper reaches of the Tachometer, but in a safe and legal way ;-)

 

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