trdsw20

please help..

does anyone know what's going on? my 99 lexus rx300 with 92000 mile , the check engine light comes on and i check OBDII CODE 0171, what can it be? i try changing the air/fuel oxgen sensor but it still come on after 20 mile..

second, my rx300 is making strange sound under the car , i will only hear it when it get to 20-30mph sound knid of rattling sound, but it's not the heat shell..what can it be..my mechanic told me cause of the gas that i put in, but i only used 93 on gas, never used cheap one..

please please help..thanks alot

Lexmex

What I would do is take it to a place/mechanic that has an advanced OBDII scanner that can read the readings off the 2 A/F sensors. I just did this the other week with a more advanced scanner to check some readings in my own RX...worked like a charm. Sometimes a bad connection with the O2 sensors can be the issue if you are still getting the light. Dirty MAF sensor will also do it. I won't go into the removing the battery cables/pulling the efi fuse in the fusebox with the vehicle off trick as I have mentioned it too many times already in a lot of my old posts.

That rattling underneath the car could be suspension related, but you might have to try to see which side. A good idea is with some one following alongside you to hear the area where it is coming from.

I don't think it would off hand be that accordion like piece that typically likes to break on our 99s as it would make something different than a rattle. I just had a broken shock fixed last week and before that it made a rattle underneath.

However, another possibility is a gasket that sits just in front of the main catalytic converter and at about the speed you are going it can make a rattle. In addition, any little piece that breaks off from the cat or into the big resonator can also make a rattle that you can't get rid of easily. I have had each of these issues.

VVT-i

You have a bad Air mass flow meter. P0171 system too lean is common for the RX300.

zombie

iTrader: (1)

yup yup! my rx still has this problem. they ran out of maf sensors at the nearest dealership to my house.

trdsw20

Air mass flow meter, where does it located?is there anyway to tell if is good or bad? how much does it cost? will i lost horse power or waste more gas?..also did anyone ever used those unerversal oxgen 02 sensor? how are they? do they work the same as oem? thanks

zombie

iTrader: (1)

the maf sensor is located near the airbox and is attached with two small hex screws. there is another thread that shows how to clean it on this forum w/ pictures.

But here is a quick version:unplug your neg battery cable, unplug the maf sensor cable, remove the two hex screws, and pull it from the airbox. use electric contact cleaner to spray the visible big wire and the two little wires hidden down the maf sensor shaft (be careful wires are fragile). let it dry completly and reinstall.

if this doesn't work then your gonna have to buy one from toyota dealership for about $150. if you continue to have a dirty/broken maf sensor then loss of power and decrease on mpg will occur.

my maf sensor looks completely clean, but friend at toyota dealership did a scan and showed it wasn't reading an increase of air when the gas pedal is applied.

trdsw20

thanks for the reply..so after you change it, no more check engine light now? before you change it, does your car make any kind of ratting sound under the car around 25mph? i try to disconnect the battery, but after i plug it back, it felt no power and can't go up to 40mph for the first couple minute then back to normal..why does this happen?

Lexmex

I don't have my stock airbox on the right side of the engine bay anymore, but look for this rectangular piece in the lower right of this photo on the intake tube. I clean this piece every week with computer keyboard cleaner.

If nothing else is wrong then the light should go off.

The rattling sound and the MAF sensor are 2 distinct, unrrelated things.

The reason when you pull the battery off and then have the hesitation is that the vehicle's computer is adapting to your driving pattern. After disconnected, it basically has no information on the outside world and needs input in order to know how to function based on where it is. This is the reason I eat a lot more MPG because of the high altitude (less oxygen content, about 25% less) due to the way the sensors read this information.

Actually, by my count it takes about 15 minutes to get fully warmed up by driving, but at the track after doing this, I need at least 1 to 2 runs to get back to where it should be.

trdsw20

thanks for the insuruction, i will try that today and hope it will works...also do you know what's the different between the oem oxgen sensor and the after market ones? now my car has an 01 lexus is 300 oxgen sensor( the one on the mandifold), i bought it by mistake and they don't take exchange cause i already install it..will this harm my rx300? or it's okay?

Lexmex

With those sensors, I generally recommend sticking to the OEM Densos as some issues have cropped up with not using OEM. Usually the issues show themselves within a week or so after installation. A bad/dead O2 sensor will just force a CEL, a fault mode. I woudn't panic over it but the only real way to tell if the O2 sensor is really functioning is to have it checked out with an advanced OBDII scanner that can read the 2 banks of those sensors and see if they are picking up readings from each of them.

trdsw20

i got it all clean, it runs excellent for the first 100 mile then the check engine light came back on..then i felt it's loosing power ..

Lexmex

It may not be the MAF, it might still be that O2 sensor and a mechanic that has an advanced OBDII scanner that can read the readings coming off each bank can examine this. You don't need to go to Lexus/Toyota for this. Lots of independents have these types of scanners. My uncle's brother has one of these and I used it the other week just to see readings. Basic OBDII scanners which are often less than $100 USD won't do this.

trdsw20

I bought a new air mass sensor at dealer cost me $150 and it was perfectly fine for the first 3 days and the engine light cam back on with code P1153... what could be wrong again

Lexmex

As I said the advanced OBDII scanner tool is your friend here. In Mexico, some charge as little as $2 USD, though I here U.S. rates are about $10 to $25 USD just to see whats up. If you want to see what I am talking about see the page of this thread in the GS forum, where we were discussing tranny coolers. There is a good picture of this device, https://www.clublexus.com/forums/sho...=280158&page=4

trdsw20

i will try to find a shop that has the scanner..thanks alot