vishesh

Hi all,

Been poking around on this forum for several years now, and running into a real head-scratcher. If anyone can help, I'd really appreciate it. I've got a 1999 RX300 with about 160k on it. I'm getting a CEL and the following codes:

• P0171 - bank 1 too lean
• P0300 - multiple random misfires
• P0301 - random misfire on cyl 1
• P0303 - random misfire on cyl 3
• P0305 - random misfire on cyl 5

Symptoms

The car idles a little rough (i.e., slight vibration), but at high speeds / high RPM, there's no noticeable effect on car operation. I think there was a slight smell of unburnt fuel in the cabin on my last trip. Other than that, car operates normally. The CEL does not blink (i.e., it is solid).

Work

I popped the hood and decided to take a look around. I didn't see any obvious problems, so I opened Bank 2, just to have a look. I know 1, 3, and 5 are the Bank 1 cylinders (i.e., nearest to the cabin). Coil packs 2 and 4 looked perfectly fine, but 6 was covered in soot and smelled a little like gasoline (see picture below). I tested each coil pack with a multimeter, and the resistances of 2 and 4 were the same as 6. Just for good measure though, I replaced the coil pack for 6. I also replaced the plugs in 2, 4, and 6, since those are easy to do.

I reset the CEL, just to see if replacing the coil pack on 6 would solve the problem. Car was fine for about 15 miles, then CEL came back on, with symptoms as described above.

By way of background, I got a P0171 a couple thousand miles ago, but it went away after I did some simple cleaning of the MAF.

Here are my thoughts:

• Random misfires can't be related to bad plugs or bad coil packs, because it's highly unlikely that 1, 3, and 5 would all go bad simultaenously.
• Since 1, 3, and 5 all started reporting misfire simultaneously, the source of the problem must be something related to Bank 1, not to any particular cylinder.

I found another guy who encountered similar codes, but it sounds like his symptoms were different.

Other than that, I'm stumped. I've spent a lot of time reading these forums and searching the web. I'm starting to think that it might be a bad air/fuel sensor (replacement instructions described here), since that would affect all the cylinders on bank 1, and would explain the fact tat the random misfire code appeared for cylinders 1, 3, and 5 simultaneously.

Do you guys have any thoughts? Any ideas on how I can narrow down the problem before I start to replace parts? I have an Equus 3130 OBD reader, so if it would help, I can read some live data from the engine and report back.

Also, I'm curious about your thoughts on what might be wrong with cylinder 6. Why was the coil pack covered in soot? Does this imply a bad seal somewhere? Could it be related to the random misfires?

uss1814

I just bought a 1999 RX 300 and had the same problems you are having

This is what I replaced.

Front bank CMP
Both right and left VVT Oil control valves (cleaned both filters all so clogged)
All the plugs and rear coil paks
IACV and Throttle Position Sensor

I dumped the oil and made sure it was 5W-30W the oil journals are very small and many times they put in 10W-30W and end up starving the VVT Oil Control Valves which lead them to operate irregulaly.

I found two vac leaks one on the vacuum control module at the base of the throttle body and one on the top of the throttle body where they Y off.

It runs like it was brand new just took a day for everything to settle in

I had a problem with the idle after everything I did but it never pulled a code and just corrected it self and a drive.

Hope this helps

You can get the oil control valves from Park Place Lexus in Dallas for $65.00 and everything else I got from Advance Auto. Little un-advertized special at Advance auto if you find a part on the internet for less than they sell it just give them the web address and they will match it.

You have to get the VVT oil control valves from Lexus as they are still dealer only parts.

Hope this helps.

John

vishesh

Hey John

Appreciate the advice. A couple questions (apologies if some of these are novice questions):

• What / where is the CMP?
• What / where is the IACV?
• Where is the throttle position sensor?
• How did you find the vac leaks?
• Were you ever able to isolate the source of the problem? Or did you just replace everything you could?

uss1814

Vishesh,

The CMP = Cam Magnetic Position Sensor - very easy to get at rear of the head by the transmission it sits right on the bend at the end of the head and little below.

The IACV and Throttle position valves are located on the throttle body itself and you need to remove the throttle boby to get at them.

The vac leaks you will see a diaphram once you turn the throttle body over this is where I found th hose cracked just for years of heat and cold.

The other you will see when you pull the throttle body off there will be to vac. lines that mount to the top of the throttle body these also were cracked just from heat.

The throttle body takes five minutes to pull off a couple of minutes to change the valves and another 5 to put it back together.

The VVT conol valves and filters are easier to change and clean with the throttle body out of the way.

John

iamhere9

I have P0171 , P0300, P0302, P0304 , P0305 and p1150 codes in my 2000 RX300 with 137K miles.
I have changed both A/F sensors, MAF and IACV, treated with Seafoam , doesnt seem to have any vacuum leaks. rough ride, high idle and bad gas mileage (14 MPG).

It started with P0171 but saw other after seafoam treatment.

any idea what I should do next ?

Lexmex

Is the check engine light flashing when you drive?

I'd zero in on the P03XX codes as that indicates an issue with the ignition coils.

How many miles have you gone since the seafoam treatment?

vishesh

For those who might be interested, I ended up just giving up and taking it to a mechanic last year. Cost me a pretty penny, as it turned out a number of components had failed over time. Air/fuel sensor ($300+ if I recall correctly), ECU had to be reprogrammed, some engine seals had to be replaced.

salimshah

Thank you for coming back and posting an update.

There are many who just ask and then we never hear back from them. Only when the OP takes time to post a final answer, we get a closure.

Salim

vishesh

No problem. If anyone wants more details on what the mechanic did, just ask. Happy to share, though my memory may be spotty since I had it done almost a year ago.

Leines

I had a similar issue, but i believe mine was different banks... i had a 171 and random misfires, i ended up replacing both OCV, and the issues went away... i also checked plugs wires, coil etc along the way... but the OCV sticks leading to misfires from my understanding.

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 (usually shown as a pending code)
• P0136 (I have only seen this one time and it was a “Pending” code)

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).

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!

Duell

For those reading my previous post I finally figured out what the problem was. It ended up being the downstream heated 02 sensor located under the driver's seat after the catalytic converters. Doesn't make a lot of sense considering the codes it was throwing versus the codes it should have been throwing if the 02 sensor was bad. But for about $50 and an hour or so, it was the solution for the nagging problem. If you want to see how to change that 02 sensor, check out the post by Lexmex on it. Great post and it made it very easy.
Cheers!

vishesh

Could you link us to Lexmex's post on replacing the downstream O2 sensor? Thanks!

Macmasdad

Go to the " Sitcky List of RX300 DYI's" and it will amongst the many great links in post #2 by Lexmex. That set of Sticky list has helped me on a number of issues.

Or copy/paste the following URL:

https://www.clublexus.com/forums/rx-...sor-2-diy.html

Duell

Here's the link to the Lexmex post on changing the heated O2 sensor: https://www.clublexus.com/forums/rx-...sor-2-diy.html

It took me about an hour ... it's not that hard if you are mechanically inclined. Good luck!