ourbudd

I'm trying to help my sister on her RX, she couldn't pass the emissions test and it was running like ____. I drove it and it seemed fine at 1st but when it warmed up it started stumbling on acceleration and missed a lot . I had replaced the coil packs 6 months ago due to 2 failures and that doesn't seem to be a problem here? I smoke tested the vac/emissions and all seemed good, I checked the fuel pressure and it stays around 58 psi while running and 30 mins after turning it off it was still at 45 psi so that seems good. AT this point after test driving it it was still running bad so I pulled the wires off of each coil to check and the front 3 seemed real good but all 3 on the back hardly changed at all. At this point I'm thinking the VVT oil control valve for the rear bank is bad, I ordered both but am open to suggestions. Below are the codes that were on it when I started. I cleared them and ran it some but have stopped and am waiting for the new VVT oil valves.

P0171 System too lean
P0303 Cyl 3 misfire
P0305 Cyl 5 misfire
P0301 Cyl 1 misfire
P0300 Cylinder misfire random
P0172 System too rich bank 1
P1133 Air/Fuel ratio sensor circuit response malfunction bank 1 sensor 1

fastnoypi

I would consider looking at the the condition of the timing belt and/or confirming if the marks still line up.

carguy07

Pop in a new A/F in bank 1.

salimshah

If we have misfires, then the we will get rich (unburnt) fuel. My recommendation would be to trace misfires first.

One way to confirm would be to clear and read the first code.

Salim

carguy07

Agreed, see what code you get first, but I have seen plenty of misfire codes due to a bad A/F sensor but not the other way around.

jbtvt

The O2 sensor is only factored into the equation after the vehicle has been running for a short time, car defaults to preset maps (open loop) until temps reach a certain point. I second that sensor. You can test them with an analog voltmeter, or at least you could on obd1. I'm sure there's still a way if you crawl under there but can't say what leads go to which wire or what the voltages should be.

You can check the vvti solenoids as well, just unbolt and give them juice. Pretty simple, and if it wasn't working I don't think it would give you codes anyway, just less hp. I made a vid on cleaning them though if you've got them out, search YouTube.

ourbudd

Well, I installed the oil control valves and reset the faults and tried driving again, needless to say it ran like ____ again, The new codes were similar. I will look at the timing belt soon especially I seen all 3 on bank 1 again. Is there a way to test the A/F sensor? I would hate to waste the money, either way I will look at the timing belt 1st an go from there.
P0303 Cyl 3 misfire
P0305 Cyl 5 misfire
P0301 Cyl 1 misfire
P0300 Cylinder misfire random
P0172 System too rich bank 1

Thanks for the help, Tim

Baetke

There is a way to test the A/F sensor but you will need a scan tool to do it because these are narrow band sensors and you can't just look at them with a voltmeter or oscilloscope. You need a scan tool to display the response times of the sensor. As an alternative you could try swapping the bank1 and bank 2 sensors and see if the misfires follow the sensor.

jbtvt

You can check narrow band with a voltmeter. You'll need an extremely responsive digital or any cheap analog to see the bounces though. https://axleaddict.com/auto-repair/H...-Oxygen-Sensor

ourbudd

So I had some time tonight and I took the covers off of the timing belt and checked it out, the marks are dead on from the crank and both cams. That would have been a sure one if it was that but no luck. I do have a handheld scan tool so I will try to see if I can tell what I'm looking for on that. If nothing else this weekend I can swap the 2 as suggested and see what happens? Thanks and back at it.

Thanks Tim

salimshah

Cam posiiton sensor can be a culprit too. You can try swapping them.

Also is there any history before the onset of problem and what could have triggered the errors.

Salim

carguy07

Err........this

jbtvt

^!

Cam sensor has it's own, different code.

salimshah

Correct, my bad

Salim

Drcoffee

wow just Wow. I spent the whole weekend changing the timing belt, water pump, seals etc and when I test drove the rx it kept throwing codes p0171, p0440, p01133, p0125. It was a real mess. For a while I thought I had installed the belt wrong. I changed the O2 sensors (they were old anyway) swapped maf sensor. But nothing fixed the problem and the engine light started to flash. I finally gave up and took it to lexus. It was a $7 vacuum hose on the evap system that had crumbled and was leaking. I could hear a slight hiss but could not find the source. I tried spraying started fluid everywhere and got nothing. So after 2 days at the dealer, they found the problem and ordered the hose. No more codes. Now he added that the evap hoses were not routed correctly. I changed those hoses when I first bought the suv, but did them one at a time so they were just as I found them when I was done. I can only think that the service station that did the tranny rebuild for the PO didnt reconnect the hoses properly when he installed the tranny. Lexus re-routed the hoses and now its back to factory spec.

the point here is that a vacuum leak could be the source of the p0171 code. I saw another post where it was the brake booster that was his leak. At the end of the day, Lexus only charged $300 for the parts and labor. I fully expected a $2,000 labor charge. What a relief to get it set right and not go broke.