1999 Lexus RX 300 with check engine light on

I have this car for about 7 months and has 55,000 miles when I got them. Now about 60,000 miles and the check engine light was on for a week and off.... Well I took to the dealer and had them replaced charcoal canister and clear the codes. After a week later the check engine light came back on. It was happened for a month and the technician at the dealer could not know what it cause to the check engine light to come back. After the third visited to the dealer they assumed that might be a Vacuum Switch Valve be a problem. How do I know if this is a problem? Can you do it yourself? Please I need some help.

we'll need a code first.

I just got a code from a local AutoZone. The code is P0171, it's has to do with MAF sensor or bank 1 ( the fuel was too lean). After filled up some gas surprisingly the check engine was off. Do you think it has to do with a vacuum switch valve in the gas tank? ( that what's the dealer thinks). Can you do this by yourself? Please help!

I'd be looking at more like a dirty or malfunctioning MAF versus an evap component for that code on that car

How can I clean the MAF? Where it located? Any suggustions.

I think that the dealership is heading the wrong direction in this case(given the information available to me). For a P0171 to set, the fuel trims would have to be unable to add enough fuel to compensate for a perceived lean condition. A leaking carcoal canister wouldn't do that for this reason: The purge valve would be closed(and no Evap vapors would be drawn into the engine) so the leaking canister wouldn't figure into the fuel strategy. If the PCM did command a purge, it would simply draw in outside air via the canister leak rather than the fuel tank(like it's supposed to) but the engine doesn't care where it's from.
No, I think that it's something else, not an EVAP problem. To have that lean of a condition, so lean that the PCM can't compensate, therre has to be a large unmetered vacuum leak, or a sticking o2 sensor.

So do you think it's a large unmetered vacuum leak or either a sticking O2 sensor. where they located? How much do they cost to replace? It's DIY kind of thing. If it does DIY, please go step by step to me. Thanks.

Visually check for any vacuumleaks, then use search feature and there's many posts explaining how to check vacuum leaks

I was just quoted $813.60 to replace the evaporator canister on my 1999 Lexus. Is that price in line or not?

Thanks in advance,

for a Lexus? Not sure!

we have exactly the same car, and just experienced exactly the same situation: CE light came up and threw P0171 code. i looked it up and it said: clean MAF sensor.
easy enough. it is located right on top of the air intake hose that comes out of the filter housing. is held in place by 2 phillips screws. i pulled it out. it looks like a long plastic tube with perpendicular hole on the end and a small compartment on the side, housing what looked like a tiny light bulb. indeed, that bulb was all covered with gunk. few shots of electrical cleaner "cleared the view". i wiped it all with a clean rag and reinstalled.
i have code reader that resets codes, so i did. will know in a day or 2 if it got fixed for good.

I too have a '99 RX300 with a studdering/misfire problem. It showed up as a P0300 and P0303 CEL, so I replaced the coil pack on the number three cylinder. It ran fine for a bit, but then started to misfire again, causing the CEL to flash, but then the engine would clean up and drive smooth, the CEL would go off, then it would act up again.

After getting a fresh tank of good gas (thought it might be bad gas), I drove a little bit and then I got a few more codes: P0300, P0303, P171. So, at this point I'm guessing it's either a bad fuel injector, a problem with the MAF, or possibly the spark plug itself. I went for the easy fix first, and cleaned the MAF. Afterwards it drove better, but there was still a faint feel of the hesitation/misfire, but not enough to trigger the CEL. I will drive it a little more, but since cleaning the MAF changed the driving characteristics, does this indicate the problem is in the MAF? Or could cleaning it just reduces symptoms caused by something else?

I'll drive the vehicle more tomorrow and report on if the hesistation gets worse again.

I'd at least check the spark plugs and see what codes return

I've been monitoring my engine for a while, and also exporing many posts online. I keep having a problem with the engine stumbling, but then it'll clear up, then stumble again. After tracking the codes I know it's either the plugs, the coil packs, or the fuel injectors. I know this because the symptoms initially all pointed to the OCV (Oil Control Valve) for the rear head (#1,#3, #5 cylinders). I just changed out the OCV yesterday and it drove wonderfully around the block. I took it for a test drive today and got a bunch of codes back. Here's what I got from a 23 mile drive in to work:

P0300
P0301
P0303
P0305
P0171
P1133

These are all pretty indicative of an OCV failure, except for getting the OCV code itself. So, I guess I'm now focusing on the fuel injectors. I highly doubt it would be the plugs (and have it throw back so many codes), but it could be.

Anybody have any other insight into what this could be? The vehicle has been getting good gas mileage, it runs very nicely for the most part, but I get sporadic 'fish bite' jerks of power loss with the CEL popping on and flashing, then symptoms going away and it running smoothly. At first I thought it was bad gas, but the more I drive it, the better it seems to be (and it runs well when the temperature is hot out). It's a strange problem. Any other ideas before I start replacing parts?

Thanks in advance!!

So I recently changed all my plugs out (and double checked to ensure they were gapped properly) with OEM equivalent NGK Iridium plugs. So far, I've replaced a couple coil packs (and rotated them), put in new plugs, replaced the OCV on the rear bank, cleaned the MAF, and ran some fuel injector cleaner in the gas. After all that, the engine runs much better now, but I can still feel it stumble and studder. I drove it to work today and by the time I got to work I had codes P0300 and P0303... random misfires and cylinder #3 misfires... same codes that started when I first had these symptoms. The vehicle always drives nearly flawlessly on the way home, but stumbles on the way in to work... seems like the symptoms may be affected by outside temperatures.

These symptoms came on out of the blue on a vehicle with 134K on the odo. I've been trying to track down the problem for the past couple weeks. I guess I'm down to the problem being a fuel injector. I can't think of what else it could be... possibly the crank position sensor?