Duell

So, we own a ’99 RX300 with approximately 92,000 miles on it. It’s my wife’s car and she got the car from a family member who has always been known for taking very good care of his vehicles. It was garage kept and obviously has low miles for the year. We are the 3rd owner of the vehicle and have owned it for about a year.
Soon after we got it (maybe about a month) the CEL came on showing a P0171 code. Then other codes – here’s a list of them:

• P0171
• P0300
• P0301
• P0303
• P0305
• P1133
• P0136

Here’s what I have replaced:
• Replaced MAF sensor
• Replaced all plugs
• Replaced all coil packs
• Replaced all fuel injectors
• Replaced OCV (on bank 1 – closest to fire wall)
• Replaced both Air Fuel Ratio sensors
• Replaced the fuel pump (not the whole unit, just the pump and strainer)

All the parts that we replaced were OEM Denso. My best friend is an ASE Tech with 20+ years of experience. He is normally the guy that figures things out when no one else can … although he doesn’t specialize with Lexus vehicles. This one has him stumped.

We have tested the ECM and it seems fine. We have swapped AFR sensors to make sure one of the new ones wasn’t bad. We have looked for vacuum leaks but cannot find one (although we didn’t do a smoke test).

I have an OBDII Bluetooth adapter and use the Torque app to see what codes are coming up and to clear them. I have also disconnected the battery and touched the + and – cables together for 30 seconds to clear the ECM. I have done this many times.

The vehicle runs rough, but is drivable. Gas mileage is horrible … about 10mpg. When I clear the codes, the first one to come back is always P0171 and lately the P1133 is quickly seen as a pending code. The vehicle has a “fish bite” kind of jerk to it (indicating the misfires) and then I will usually see one of the P0301, P0303, or P0305 codes first, and then the P0300 (but sometimes the P0300 is one of the first codes to come on after the P0171). And lately the P0136 code is showing up as well.

One other thing we haven’t done so far is a fuel pressure test, but I thought by replacing the fuel pump that I would not need to do that test

Any thoughts or suggestions would be greatly appreciated!

carguy07

Wow that is a ton of parts! I would concentrate on the first couple of codes that are popping up. So B1S1. Maybe the wiring harness to it has an issue or there is a crack in the exhaust manifold?

maxSteel

It seems really unlikely you needed all that stuff.

P0171 cause could be as simple as a loose hoseP1133 is B1S1 sensor, but the procedure says if there are other codes check that first

Z07

IMO start with the lowest code first.

P0136 Visually inspect the harness for the post cat O2 sensor and note that sensor's performance in Torque. It should be slower and lower magnitude when compared to the pre-cat O2s.

Using a non-contact thermometer, drive the RX for a short trip or let it idle for a while and compare the temp of the exhaust pipe before the cat to the temp of the pipe just after the cat and expect an 80-120 degree rise from the catalyst "burning" the excess fuel.

If the cat checks out then replace the post cat O2 sensor and clear codes to see if/what recurs.

----

The P0171 makes me suspect an induction leak and could be the root of all the other trouble.

Use starter spray in the area around the intake particularly between the MAF and the intake manifold. A rise in RPM here indicates an induction leak. Continue on to the vacuum lines until you've probed them all. Don't forget the huge vacuum line to the brake power booster.

Ref:

Duell

Thanks for the replies. I realize that I probably didn't need all of these parts, but it was done over time mostly through a process of hunting down the culprit. The good thing is that once I do get this figured out, I won't have to worry about these for a long time.

So I will do some more checking for a vacuum leak using the starter fluid and check the post cat 02 as well as checking the cat with a thermometer.

I'll post my results.