2000 RX 300 running rich

Problems started a few months ago. Firstly the smell from the exhaust in the morning has changed and started to smell like unburnt fuel. I then used a cheap scan tools and it showed up MAF sensor and O2 Sensor code. My mechanic then replaced the MAF sensor and found the O2 sensor wire were broken so he has that replaced too. My car used to be able to do 300 miles to the tank and now it can barely hit 180 miles to the tank.

Scan data are showing
Short FT #1 3.05%
Long FT #1 30.42%

Short FT #2 3.01%
Long FT #2 30.42%

O2FT B1 S2 99.01%

No fault DTC.

Any suggestion? Perhaps vacuum leaks or exhaust leak before O2?

TQqqqqqq

Wow, 30% long term with no code? :ohmy: This thing is taking it's time to turn the light on!

What conditions were your trims taken? Idle, or driving? Knowing that will help us pick a good diagnostic direction. Also, you can safely ignore that O2FT B1 S2 PID. That's a default value, and not an actual fuel trim correction. Another user actually asked this same question earlier .

If those trims were taken at idle, then a vacuum leak is suspect. We'd want to compare those trims to the values seen at 1500 and 2500 RPM, to determine if we're truly looking at a leak. An exhaust leak is unlikely, IMO - the upstream leaks would have to be HUGE to cause this kind of trim problem.

Get back to us with your fuel trims at idle, 1500 and 2500 RPM, and we'll figure out the next step!

@Tyler thanks for your quick reply. I just drove to my friends house to get the scan data. Below are the data for idle, 1500 rpm and 2500 rpm.

@Idle
Short FT #1 3.09%
Long FT #1 30.42%

Short FT #2 3.87%
Long FT #2 30.42%

@1500 rpm
Short FT #1 0.74%
Long FT #1 28.86%

Short FT #2 3.09%
Long FT #2 30.42%

@ 2500 rpm
Short FT #1 -2.38%
Long FT #1 27.30%

Short FT #2 3.09%
Long FT #2 30.42%

Looks like the Long FT #2 isn't moving

Also.. Not sure if this relates to the fuel trim problem or not. As this problem started a few months ago, something strange happened every time I am at the pump. I just couldn't fully depress the gas pump nozzle. If I fully depress it will shut off on me and so the only way of filling the tank now is to do slow fill.... Very very slow. My mechanic is suggesting the charcoal canister is bad.

Hi…
I would look at the PCV system and if that checks out Move to the purge solenoid and test for vac leaks and make sure its working like it should. I would also check the vapor pressure sensor in the gas tank this can be best done with a bi-directional scanner…


Just some starting points!!!

Let me know how you make out…

Doc n2mx

jefrileang wrote: @Tyler thanks for your quick reply. I just drove to my friends house to get the scan data. Below are the data for idle, 1500 rpm and 2500 rpm.

@Idle
Short FT #1 3.09%
Long FT #1 30.42%

Short FT #2 3.87%
Long FT #2 30.42%

@1500 rpm
Short FT #1 0.74%
Long FT #1 28.86%

Short FT #2 3.09%
Long FT #2 30.42%

@ 2500 rpm
Short FT #1 -2.38%
Long FT #1 27.30%

Short FT #2 3.09%
Long FT #2 30.42%

Looks like the Long FT #2 isn't moving

Yeah, the total trims never get much better, do they? I'd move away from a vacuum leak, then, and go towards fuel delivery.

Does this thing feel like it has low power? 'Cause I'm wondering if the MAF sensor is overreporting, causing a lean condition across all load ranges. Could you grab some more data? I'm interested to know what the MAF reads at a hot idle. Theoretically, it should be just above 3.0 grams/second.

I know that your MAF was changed recently, but I'm somewhat suspicious of the replacement part.

I wonder what the upstream o2s are doing...