bchehab

Hi.

I've been reading and reading in this great forum and it has been a great help. but recently I came across a problem which I will describe.
I own an RX 300 1999. with 63500 miles. 2 weeks ago, suddenly the car jerked, and the overdrive stopped working and the fuel consumption got so high. the scanner showed the P0300, P0301, P0303 and another code which I don't really remember but saying something about "main relay 1"
the Mechanic changed the 3 coils located in the back and all the spark plugs. cleaned the injectors. the car ran smoothly. but 3 days later and unfortunately it was the weekend, the car did the same. as I was war from home and I didn't want to drive a long distance in this situation, it came to my mind to reset the ECU by pulling the battery cable for 10 minutes, and so I did, and the car came back to normal again.
I really don't know how to interpret this situation and why it worked again. but it is possible that the problem will occur again and again, but what is the real cause of this ? I really appreciate more info or ideas on this.


P.S: I live in Beirut - Lebanon and the fuel we have in this country is regular 95 octane and premium 98 octane.

Lexmex

Welcome to the Club.

You'd have to really check the codes and see what occurs the next time. One of my theories, and it's NOT supported by the service manual, is that a misfire causes a batch of unburnt fuel to go directly out into the exhaust fries the precat (that has happened to me, but the coil was okay) and causes an A/F sensor to get partially damaged (hasn't happened to me, but I have seen this on other cars). Reading the A/F sensor in turn shows it isn't functioning quite as normally as the other A/F sensor on the undamaged bank, but on occasion say one of the A/F sensor OBD2 codes related to degradation of the sensor, like P1153 for example (I got that once as a pending error), might or might not show up, or shows up as a pending error.

In short, there might be some partial damage to an A/F (air fuel) sensor that may not show itself, but could be causing a repeated symptom. With a slightly damaged A/F sensor, this would in turn cause the amount of fuel to vary ever so slightly entering the combustion cycle with an inappropriate amount of air, and thus a misfire. such as P0300 which is a general across the board misfire, not tied to any cylinder in particular.

Main Relay 1 might have been something related to the ABS (Antilock brake) sensors. You would know there is a problem here because you would feel some jerkiness on the brakes as you came to a stop (when under 10 km/h or so)...feels like the brakes are disengaging for a second. Certain OBD2 sensors might bring up the codes differently for this, but it sounds some very similar to ABS.

What pulling the battery does is reset the settings in the vehicle's computer. This is a good idea any time you get something like a misfire, in order to let the vehicle get a fresh start with new readings, not the old ones that caused the problem.

I had a college roommate at Georgetown who was from Lebanon and he also confirmed to me the higher octane gas. That should not be a problem with your RX300. I used to experiment with 100+ racing gasoline in Mexico and even at high altitude (where lower octane gas should be run but the lower octane stuff in Mexico was not as good in quality as the Premium) I had no problems whatsoever, the engine timing can adjust to that gas without issue. Since you near sea level that's even better for the higher octane gas.

Where I live now in Florida, we have 10% ethanol in the gas and that actually raises the octane in the gasoline a few points. I use a 93 octane Chevron here, but the only drawback with 10% ethanol is that we lose a bit in km/liter, but you will not have to worry about that in Lebanon.

bchehab

Thank you Lexmex for your big help and Support.
Although the car is running smoothly still, but today I took it to the mechanic and the scanner showed the following codes:
- P0125 (Insufficient Coolant Temperature for Close Loop Fuel Control)
- P1135 (A/F Sensor Heater Circuit Malfunction Bank 1)

I would like to mention that my gas mileage is not bad. an average of 18.5 mpg.

one more thing to add, here in lebanon mechanics have a bad habit of removing the catalytic converter and mine was removed and replaced by just a regular exhaust of the same size. what effect does it have on the car ? since it was removed the CEL is always on.


once again thank you for your support

salimshah

Although I dont recommend clearing the codes blindly, but there are cases when the first error code recorded causes a chain reaction, and more codes are thrown. If such is the case, one should try resetting the codes and read on first CEL.

The catalytic conv, tries to capture/neutralize unburnt gasses. We share the same environment, you are in Beruit and I in Texas. By removing the cat. you get improved exhaust flow and more power. The exhaust sensor for you may be missing ... in any case yiur ECU is registering a value which is causing it to give you CEL. Worse still, the ecu would be trying to adjust and skew your fuel to air mixture. May be some one can tell us if that would increase the gas or reduce it.

Salim

Lexmex

Salimshah already touched upon several of good points, and I'll add a few things as well.

18.5 mpg is not too bad. I run over 20 mpg on 93 octane Chevron, but my RX is quite modified as most people in this forum will attest to.

Now in relation to your codes, P0125 is probably a complementary error to P1135, which is related to the A/F sensor bank 1 sensor 1 (shown in the photo below) and it is behind the engine block. In the U.S., they go for under $200 USD each.

Now, here is what I would do. I would have a mechanic with a scanner examine the readings off both Bank 1 and 2 (sensor 2 is visible in the engine compartment just behind the radiator and on the front of the engine block). See if both banks, especially bank 1, have readings that do not deviate too much from each other. That is too confirm that you don't have a problem with the A/F sensor itself. In my experience, if both banks are showing readings, don't spend $200 USD, because at 18 mpg you're doing okay.

Second, I take it the mechanic took out the catalytic converter beneath the vehicle and replaced it with exhaust pipe. The reason I ask is that there are also 2 precats, catalytic converters that are before the main catalytic converter. Removing those precats will not cause an error (there is a vehicle sold in the U.S. known as the Toyota Solara that has a similar 1MZFE engine and the non-California spec vehicles run no precats). However, there are a few possibilties that can occur without running the main catalytic converter under the vehicle.

1. P0171 (lean error and also occurs if there is an exhaust leak)
2. A/F sensor error (that is what you have)
3. P0420 Catalytic (Converter) System efficiency below threshold

P0420 I know well from vehicles my uncle and I worked on in Mexico, bad, high sulphur gas, thin air and worn catalytic converters can create this nice little code.

P0171 I have seen recently when we had to repair some damage to my exhaust pipe caused by a tire place just recently.

However, A/F sensor error right on the rear bank is also one such possibility. Given that you are getting 18 mpg, I think you are probably okay.

Now, having the catalytic converters stripped off will indeed as Salimshah pointed out give you more power. There is a small scavenging effect that will pull some gas through the exhaust faster than normal, but this caused through natural scientific laws and not the vehicle's computer.

So to sum it all up. Have the mechanic if possible check the readings for banks 1 and 2 for your A/F sensors (sometimes they call them O2 or oxygen sensors) and see if they both have readings and do not deviate too much from each other. Let me know if this is possible to check this.