JHagan88

I have a 1999 RX300 with 101,500 miles. I've owned it for about 4 years now and I've always serviced it when needed. I haven't had any major issues with it other than the starter going a few years back, but now I am having nothing but issues recently. I've been researching for solutions, and replacing parts, but to no avail.

This all started about a month ago. I got trapped in a HUGE storm and was driving down the highway (only going about 30MPH) and then suddenly hit a huge body of water. The highway was flooded in that spot. Everything SEEMED okay up until later that day. When the storm cleared and I got back in the car, my CEL came on for the first time ever on this car. I ran the codes and I was getting misfires on 1, 3, and 5. I couldn't actually hear any misfires though, so I was confused. Then when driving, I noticed an exhaust leak. I got under the car and noticed the 02 sensor (after the cat) was hanging down. It seems that when I hit the body of the water, the studs that secure the 02 sensor in place snapped off.

So I then installed a brand new catalytic converter and 02 sensor. Drove much better after that, obviously. The CEL was still on, though. Still getting misfires on 1, 3, and 5. So I turned to the OCV (VTT Solenoid). I took out the bank 1 OCV and cleaned it. It drove perfectly fine for 200 miles and then the CEL came on again. Now it was driving fine, but on the highway going about 60MPH it would be running at 4K RPMs! So I replaced both OCV's on bank 1 and bank 2, today actually.

Now this is where I am. I still have the CEL, still reporting misfires on 1, 3, and 5. However, now I am getting fault codes for "Bank 1 Too Lean" and fault code P0125 "Insufficient Coolant Temperature for Closed Loop Fuel Control." It's idling fine, and the engine seems to be working perfectly normal up until I hit the highway and the RPMs get higher than they should (still around 4K). I am standing in front of a wall right now, with no clue on what to do. I don't know if it's my bank 1 02 sensor, MAF sensor, thermostat, ignition wires, I have no clue what to do. That's why I've turned to you guys, I could really use some advice and suggestions.

I greatly appreciate it in advance.

carguy07

That sounds like an air/fuel sensor to me. What code are you getting that says it's too lean?

JHagan88

Code is P0171 "System Too Lean (Bank 1)"

JHagan88

I'm still confused on the bank 1 misfires, though. I had them since before the P0171 fault code.

So right now these are the fault codes that I have:

P0300 - Random Misfire Detected
P0301 - Cylinder 1 Misfire
P0303 - Cylinder 3 Misfire
P0305 - Cylinder 5 Misfire
P0171 - System Too Lean (Fuel Trim)
P0125 - Insufficient Coolant Temperature For Closed Loop Fuel Control

maxSteel

I would usually say clear the codes and then start with the first one that shows up.

Reading the below and given you had an exhaust problem maybe you still have an exhaust leak.

The diagnostics guide says

Priorities for troubleshooting:
If troubleshooting priorities for multiple DTCs are given in the
applicable DTC chart, these should be followed.
If no instructions are given troubleshoot DTCs according to the
following priorities.
DTC P0171 System too Lean (Fuel Trim) (Bank 1)
DTC P0172 System too Rich (Fuel Trim) (Bank 1)
DTC P0174 System too Lean (Fuel Trim) (Bank 2)
DTC P0175 System too Rich (Fuel Trim) (Bank 2)
CIRCUIT DESCRIPTION
Fuel trim refers to the feedback compensation value compared against the basic injection time. Fuel trim
includes short–term fuel trim and long–term fuel trim.
Short–term fuel trim is the short–term fuel compensation used to maintain the air–fuel ratio at its ideal
theoretical value.
The signal from the A/F sensor is approximately proportional to the existing air–fuel ratio, and engine ECU
comparing it with the ideal theoretical value, the engine ECU reduces fuel volume immediately if the air–fuel
ratio is rich and increases fuel volume if it is lean.
Long–term fuel trim compensates the deviation from the central value of the short–term fuel trim stored up
by each engine tolerance, and the deviation from the central value due to the passage of time and changes
of using environment.
If both the short–term fuel trim and long–term fuel trim exceed a certain value, it is detected as a malfunction
and the check engine warning light lights up.
DTC No. DTC Detecting Condition Trouble Area
P0171
P0174
When air fuel ratio feedback is stable after engine warming up,
fuel trim is considerably in error on RICH side
(2 trip detection logic)

• 
  Gas leakage on exhaust system
• 
  Air intake (hose loose)
• 
  Fuel line pressure
• 
  Injector blockage
• 
  Mass air flow meter
• 
  Engine coolant temp. sensor
• 
  A/F sensors (bank 1, 2 sensor 1)

P0172
P0175
When air fuel ratio feedback is stable after engine warming up,
fuel trim is considerably in error on LEAN side
(2 trip detection logic)

• 
  Gas leakage on exhaust system
• 
  Fuel line pressure
• 
  Injector leak, blockage
• 
  Mass air flow meter
• 
  Engine coolant temp. sensor
• 
  A/F sensors (bank 1, 2 sensor 1)

HINT:

When DTC P0171 or P0174 is recorded, the actual air–fuel ratio is on the lean side. When DTC P0172
or P0175 is recorded, the actual air–fuel ratio is on the rich side.

If the vehicle runs out of fuel, the air–fuel ratio is lean and DTC P0171 or P0174 is recorded. The check
engine warning light then comes on.

If the total of the short–term fuel trim value and long–term fuel trim value is within ± 35 % (80
C (176
F)
or more), the system is functioning normally.

The A/F sensors (bank 1, 2 sensor 1) output voltage and the short–term fuel trim value can be read
using the hand–held tester.

The engine ECU controls the voltage of AFL+, AFR+ and AFL–, AFR– terminals of the engine ECU
to the fixed voltage. Therefore, it is impossible to confirm the A/F sensor output voltage without hand–
held tester.

maxSteel

DTC No. P0125

Detecting conditions

• After engine is warmed up, A/F sensor output* does not change when conditions (a), (b) and (c) continue for at least 1.5 min.
• *: Output value changes at inside of engine ECU only.
• (a) Engine speed: 1,500 rpm or more
• (b) Vehicle speed: 40  100 km/h (25  62 mph)
• (c) Throttle valve does not fully closed
• (d) After starting engine  140 sec

Trouble area

• Fuel system
• 
  Injector
• 
  Ignition system
• 
  Gas leakage on exhaust system
• 
  Open or short in A/F sensor circuit (bank 1, 2 sensor 1)
• 
  A/F sensors (bank 1, 2 sensor 1)
• 
  Engine ECU

BTW google RX300 Diagnostics pdf

AnthonyMtz

First of all you're getting the lean codes from the misfiring, would I suggest you to try is swap the coil packs with the ones in the front and vise versa, also inspect the spark plugs.

JHagan88

So I have been killing myself trying to find out what could be the problem here. I've narrowed it down to a possible electrical issue. I've cleared the codes and the car is driving perfectly normal at the moment. The CEL has not come back on yet. What I did notice today was this....

1) Windshield washer fluid is not working on front or rear.

2) Rear driver-side door not locking/unlocking

I've checked the fuses and they are all good.

maxSteel

I don't think those systems have any relationship.

The windshield washer pump is in front of the right front wheel. Same pump for front and rear. Maybe the connector or motor got damaged by the flood.