Spencer55

Hello to all. Not too long ago, I purchased a 2002 Rx300 AWD with 115k miles. I bought it knowing it needed a transmission! Upon inspection, he told me that it also has an intermittent idle problem.. but I don't like going home empty handed. Fast forward weeks of headache, I'm still puzzled, and there's a few hints that make this case actually susceptible for forum diagnosis. The hardest part of this diagnosis is not knowing which problem came first or if they're intertwined like a bad ecu.

Keep this in mind the entire time reading my symptoms.. the erratic idle, low idle, high idle will settle and PUR like a kitten when my OBD2 monitor is hooked up. Even before I power the monitor on, it acts better with a blank OBD2 hooked up. Also, there are never stored codes, only manufacturer specific pending codes for the following:

Vvt/camshaft bank 1 (P1346)
Vvt/camshaft bank 2 (P1351)
Misfires on every cylinder 1-6 (6 separate codes)
A/F sensor (p1150)
And occasionally, a shift solenoid B electrical (P0758)

This set of codes came on together the most consistently after several erases. The engine light won't even come back on until I unplug my monitor lol. However, it has before just shown bank 1 with 2, 4, and 6 misfire. Vise versa, I've seen it only throw Vvt bank 2 with the 1, 3, and 5. I've also seen misfire codes for all cylinders with no Vvt codes, only the A/F along with them.

I'm aware Vvt solenoids can cause an entire bank to misfire, I changed closest VVT with an O'Reilly''s part but from now on will use OEM..but I'm getting codes for both banks. I have cleaned the filters underneath the Vvt solenoids. I swapped A/F sensor to see if the code would also transfer banks.. it didnt. I took off and wire brushed the grounds, I'll double check to make sure I indeed hit them all.. I can't even think straight knowing the car runs like crap, runs fine the second I plug up an OBD2 , and resumes running like crap the second I pull it out. No transmission differences driving with OBD plugged up, acts like I solve a vacuum leak once I plug it up.

There's nothing else to do but to throw parts at it because I'm not experienced to read and understand the live data output. Not competent enough for wiring specs input and output..

The last time I fooled with it, I just let it run well for a while while plugged up... didn't work. Then I tried again but a little longer.. didn't work. I sat there dumbfounded and before I gave up, I unplugged it and it didn't surge. It continued idling fine and a check engine light didn't come back on for several minutes after unplugged, and that's where I left off, but the transmission still presist.

Transmission is taking way too long to go into 2nd, then punches it into 2nd, too firm, too much pressure. THEN, right as you anticipate 3rd, the transmission fully disengages for about 5 secs before bumping into 3rd. It's like it's in neutral, I can float the tachometer during this "drop off" between 2nd-3rd. For diagnosis purposes, I've been Rev matching it before it eventually shifts lol. First thing I did was drop the pan and change fluid with filter and Toyota fluid. The fluid looked and smelled fine, the magnets just had that typical sludge, and the filter was typical, little heavier than the new. Thats the reason I was in the market for a 100k mile lexus needing a transmission, I had a hard time believing a lexus transmission ate itself up. I gave a thousand bucks for it..

I can't even imagine what advice someone could give me that I don't already know.. if nothing else, I want to have a thread that's more helpful than I've been able to find, and actually update it when I fix it. I havent checked the timing because monitor connection wouldnt correct a jumped tooth intermittently. I think anyone would suspect an ecu at this point. And also, my battery has been dieing overnight every night since I purchased it. I'll swap batteries and see if that helps.. maybe that's why it finally ran fine after it ran so long the other day. will keep this updated. Thanks for the read.

Audiqv8

The car only runs well when you plug in the code reader. Get an ohm meter and check pins 4 and 5 of the OBD they both should be ground with zero ohms. There is a chassis ground and a dedicated signal ground. My guess is that the signal ground is missing or has a high ohm reading. The OBD is bridging the two grounds. You can clear the code and drive around with the OBD plugged in to see if the codes return and to see if performance improved along with transmission shifting. HTH

Spencer55

That's incredibly helpful and insightful. It's also smart. I have an ohm reader, just didn't know what to check for and at least now I have a lead, so thank you. More than likely I'll have results before the days out. The only part I'm confused at is:

If the monitor plug-in was bridging the ground..in electrical terms, I'm assuming this means it's sharing a ground. And if it requires a bridge to be grounded, when it obviously wasnt meant to be bridged, what exactly would I trace if my Pin 4 or 5 showed current. I notice pin 4 is for chasis ground, but what is a signal ground.. ecu, right?

Tjackson

I have similar problem. 2001 rx300, p0301, p0303, p0305, then eventually a p0300 and a p0758 shift sol. B electrical. Initially vehicle had knock sensor codes which I replaced, twice and those codes never returned.I have changed oil controll valve, ocv filter, plugs, coils, shift sol. Checked wiring and grounds, cleaned maf sensor and even changed the ECU, which also controlls the tranny. Severe misfires on startup untill engine dies. I have to give it some throttle to get it to idle and then it idles smooth and accelerates ok. Transmission has a delayed 1-2 shift that then bangs into 2nd gear and the 2-3 seams to neutral then bang into 3rd 2 or 3 times untill it is engaged. I also changed valve body. Pan was clean, fluid was great. I am stumped.

Spencer55

Wow.. I was wondering if I should try an ecu next.. now I'm even more hesitant. Now that I'm stumped as well, I'm forced to back track and doubt little things.

Which parts did you use for the VVT valves? Did you use OEM Denso or aftermarket? I truthfully forgot what bank has what make of part, but I know they're not OEM and now I'm tempted to buy OEM VVT valves, and these RX''s have a A/F sensor on the manifold, looks just like a o2, that I also replaced with duralast or something. You'll notice that the front A/f sensor is somewhat linked to the wiring for the VVT. I'm looking at close to 400 bucks if I re-buy all the OEM sensors though.. and throwing parts at it was never my style..

And although I cleaned under the grounds, tried scraping the paint off underneath, ect, doesn't change the fact that my battery terminal is slightly corroded.

Do you have any similar characteristics? Also, it would be interesting to see yours also run better with an obd2 monitor hooked up to it. Was your transmission problems and idle problems synomenous? I bought mine like this, so I don't know how linked they are.

Audiqv8

You can skip to 13:25 to see how AF sensors are tested. Why not change the battery terminals if they are corroded?

thomas1

that was very interesting, like the comparison on the O2 sensors.

Tjackson

I got it fixed!! There are two grounds on the back of the intake. A previous mechanic had failed to attach the smaller one and it was tucked back where you couldn't see it. These are very hard to get to since they are against the fire wall. Once I connected the ground all my codes wnt away and the car drives perfect, no malfunction lights or anything. Weird how that particular ground caused a shift solenoid code and misfires on 1 3 and 5 and that weird 2-3 shift. Btw all parts i used were aftermarket, from pep boys. They all work fine now. Hope this helps ya'll out!!

maxSteel

That's awesome news. Best kind of fix.

Spencer55

Man, that's good news. I'll be checking back there near the firewall again, I doubt I'm completely missing a ground wire though, I won't get so lucky. I'm going to tackle mine tomorrow because I finally got a new ohm reader. It would be cool to find a diagram for all the grounds. Maybe post a pic if the ground that was so hard to see.

Spencer55

There are descriptions under the photos.

I've been hooking the black wire to a positive and reading the ground points. Every ground point read neg (-)10. ??



Prong number 5 is indeed "missing". Looks like a lot of them are missing. My number 4 prong for chasis ground seemed to have a reading. My voltage gauge apparently doesnt have the proper setting for DC? But i dont believe it was suppose to show numbers on prong 4.

This is prong 4. This meter wouldnt read anything but this setting. This setting read 12 while hooked up to a pretty dead battery.

Audiqv8

Not the way I would test for ground, hooking to the battery and probing the OBDII connector. Instead I would use the Ohm setting on the meter (one click from the Off Position) and instead of hooking the black wire to the pos battery side I would hook the black wire to a chassis ground and probe the OBDII connector. The meter should read 000 if there is a ground. If there is no ground it would read OL. By hooking the meter to the positive battery terminal you could be sending 12v to something that might only be used as a signal wire. Yelp you are missing ground on pin 5 which explain why the car needs the OBDII to make it run. BTW that is an Amp Clamp meter usually used in measuring amps and high AC (alternating current) voltage like in an Heat pump or Air conditioning unit not really that useful for DC current.

Audiqv8

Ground location for a RX300 AWD. The triangle indicates ground location.

Spencer55

Yeah, didn't take long to realize I didn't have the right meter.. I never did check the ecu output with the battery, I was using a ground in the door jamb and was reading those numbers on prong 4.. but those numbers mean nothing bc I dont have the right ohm meter for DC. I am confused as to why you assumes my 5 prong would be missing, and it is. It doesnt have a metal prong inside the fitting, does that mean someone has removed it or tampered with it?

Spencer55

I realized which ground you were talking about hours before going on a trip out of state. I'm just going to take the plenum off. I can tell someone's been in there before. I bought it from someone who took it to a mechanic that couldn't fix it... so that middle ground is my number one lead. I'll have the plenum off in 15 mins with that electric milwakaki.