twinengine

Well, I'm new to this board, but I have a few issues now with my 1999 RX300 at around 126k miles. It's been a great car (we bought it at around 80k in 2003)...little, if any, issues!!

The problem that I am having now is that my car is getting bad gas mileage (around 11-12 miles per gallon in the city), and upon computer check, the code read-out says CODE: P0171. I've read on this board that it could be a few things, and not necessarily the sensors. The check engine light has been on for a looooong time (yes, I know that's bad, but I continued ignoring it, knowing that it wasn't life threatening, and I didn't have the money to fix it then, I know STUPID, HUH?! ), and the car knocks when I step on the gas pedal to accelerate really fast (it doesn't knock if you accelerate really slowly though). I really, really think the problems are connected. The system is either running too lean or too rich.

Here are items that have been recently fixed or updated:
-fuel injectors cleaned
-new water pump
-new thermostat
-2 new radiotor hoses
-2 new serpentine belts
-new radiator coolant
-new timing belt
-new timing belt tensioner pulley kit

So, I am wondering if anyone has encountered this problem. I need to get better gas mileage for understandable reasons!! I haven't had the spark plugs replaced yet, but I doubt this is the whole problem. I am also scared my car won't pass inspection (I'm in TX)....don't want to fool with that, so I'd rather get it fixed.

The shop my dad talked to (and he has to reallllly trust a place before he will give them a car to work on, and he knows his way around an engine) said they could likely fix it for $110-$200....hopefully meaning that it isn't a big problem (and that includes parts + labor).

BTW- I am totally clueless when it comes to this stuff, but I am a single parent and don't have the time, patience, or MONEY $$$ to fool around with this, so my dad did me a favor to call around (and he's 5 hrs away, so it's hard to get there to get it fixed).

PLEASE HELP IF YOU HAVE ANY IDEAS!!! Thanks!

salimshah

Are you a DIY? If not then go for thr $100-$200 solution. You will recover your cost by saving gas.

If yes, then the MAF sensor needs attention. There could be other sensors too, but start by checking and cleaning the MAF. Reset the light by disconnecting battery for 30mins or so. The problem can also be in the AirFuel ratio or the knock sensor.

Salim

twinengine

So, it sounds like the mechanics should go with the MAF sensor first? I hate to play hit-and-miss.....is there any way they will know for sure what it is first time around?

And what is the MAF sensor?? Sorry, I don't know!! I am clueless!!

Thanks!

LiqrSicc

Do a search, theres a bunch of threads on the MAF. At your mileage, you're due to change your spark plugs. I had the same problem recently and it was a bad ignition coil.

Lexmex

Here are some MAF pictures.

The location is just behind your airbox on the right side of the engine bay. A Philips screwdriver should be enough to remove it. I have highlighted the location in yellow.

Lexmex

Once you remove it, you will see this diode. It may have some accumulation (dirt or other) and should be read and clear if clean. There are two things that I find clean without issues (I used to use brake dust cleaner but not anymore): Electrical contacts cleaner or Computer keyboard cleaner.

Clean off the diode with this.

Lexmex

And then the two threads. These are located in side the sensor. Just squirt the contacts or keyboard cleaner into this slot.

Afterwards shake it and let it dry for a bit...like 5 to 10 minutes.

salimshah

When you pay some one then you should not diagnose it for him/her. The right appraoch is decipher the code and sequentially follow the itmes as the sensors/engine_condition are all inter-related. These days mechanics start replacing itmes one by one till the problem is solved. They never take anything back (for mulitple reasons ranging from labor time to resale of used part etc).

Your are faced with DIY or pay the mechanic, There is no point in overthinking it.

Salim

Luthor

Off the wall I know, but it sounds like my 92 LS400. At 245000 my check engine light has been coming on, and I put electrical tape over the little light that 3D its way onto my dashboard. Except that I got part of the TRAC light so it only said TRA. I just kept on pulling my fuse out and reseting the light. It will be minor Im sure.

I almost bought a 99 RX300. I had a bad day just like the Daniel Powder song, except I took 2 others with me. No one was hurt, so I can joke. A couple traded in a 99 RX300 and a 95 LS400 for an 07 RX350. After totalling the 92 I just wasn't ready to say good bye to the sedan. And my dog is a Minuture Schnauzer; but Buddy the German Shepard/Border Collie mix (the Dog that I sit for, and he loves me more that I like him, and I like that dog alot. Maybe he was my dog in a past life, J got him from the pound, so who knows) gave me the most pathedic said eyes I have ever seen as I took J to go car shopping, and we were in the two door Accord with my Grandma already in the back.
SO I almost got the RX just for the space. (Buddy's favorite rental car was the SRX)
But as I said my Schnauzer doesn't need space. I have been spoiled by the LS and I cant imagine the RX riding as smooth and having as much power, but I pay for it in gas. OR they may be actually pretty close, assuming the RX runs on premium.
So I will wait till something Bad happens to the Two door Accord for the RX.

I am sure that yours is minor.

When I changed the sparked plugs at 215000, the car ran alot better. The check engine light came on to, but it would go out by just turning off the car and reseting it.
Best of luck!

SteveH

I had a similar problem poor gas mileage sluggish and intermittent CEL I cleaned the MAF and it seemed to clear for awhile but just recently it appeared I got a sound like the muffler rusted out but only really noticeable at low speed. Come to find out after a search here that the 99's were prone to having a poor design exhaust manifold, which they fixed in 2001. Lexus replaced the manifold and got me for the O2 sensor, it appears to run better amd I will be checking to see if there is an gas mileage improvement. Really too bad that the problem didnt show up sooner or someone caught it during the normal inspections and service and save part of the $1400 now to fix it.