99 GS400 - 282k miles - First Post

I promise I've scoured the forums. If this issue is there, maybe I'm just not describing it right, thus I'm not searching for the right symptoms. I've read dozens of posts and I'm not any closer to figuring this out.

The car runs really good nearly all of the time. It seems like sometimes when I hit bumps, the engine just turns off. It's like the key was turned off. 99% of the time it will bump itself back started since I'm rolling. Occasionally it does it on the highway, with cruise control on, it will hesitate like it was missing or fuel cutoff, sometimes several times in rapid succession.

It's done it when the car was sitting idling. Sometimes this will cause a check engine light, and the VSC warning light to come on.

Codes: P0100, P0420 ( I know P0100 is a MAF code and P0420 is "catalyst system efficiency") When I got the car smogged I put a tank of that guaranteed to pass and it went away. I think right now both are pending codes, My CEL is off.

The thing is, I've replaced the MAF. When replaced it didn't make any difference, I've cleaned it, no change. I've tried disconnecting the MAF and the car doesn't seem to drive any different. The other day I pulled the OCV VVT solenoids to have a look and they are fine. They work. No vacuum leaks that I can tell. Spark plugs are new. Air filter is new. Oil has been changed.
Is it possible I got two bad MAF's in a row? I have the factory service manual, I'm going to check resistance today.

A few months ago I was watching the fuel trim and it seemed like one bank was high. Also, the O2 sensor voltages were not in alignment with things I read here in the forums. I don't recall what kind of numbers we're talking about anymore, so this may not be as relevant.

I've got a laptop with the Toyota software so I can check whatever. Completely comfortable getting my hands dirty.

Much appreciation in advance.

 

I guessing here, but I still suspect you have a leak somewhere. It explains most of the symptoms you describe and will cause the P0420 code. How are you looking for the vacuum leaks? A pinhole size leak can be difficult to detect.

 

I went over everything today, misting the all over the engine with both water and starting fluid, and i'm not detecting anything. I've worked through random misfire codes, the result of giant vacuum leaks, and this car isn't running like that. It's never stumbling or struggling to maintain idle. I'll try poking around tomorrow with a vacuum hose to hear if I can hear anything.

I'd like to emphasize how intermittent/random this is. A couple months ago I drove from San Diego to Phoenix and did not experience a single symptom. I even got decent gas mileage. Drove the whole way on a single tank. By contrast, around town, I'm getting around 15mpg, and I'm really not lead footing it. Lot of short couple mile trips.

 

It is very possible to get a defective MAF these days. Especially if you went with a Duralast or other cheap parts store part. They seem to have a hard time getting them right. I've had up to three defective in a row from Autozone, and on more than one occasion trying to repair cars at my shop. Napa is your best bet for quality control, but still not great. Not saying yous is bad, but it is not a far stretch to say it's defective depending on what you put in.

 

I will investigate this possibility. I bought the MAF from ebay, it was described aftermarket new, but I suspected it was oem used. Both it and the original have the correct resistance per the specs in the factory service manual. One thing I thought interesting though, is the car will die immediately if I unplug the maf and throw the code with the vsc light.

 

Update; I went around the engine compartment with a hose up to my ear and I can't hear any vacuum leak. I've gotten the code again, at slow driving speeds, that didn't seriously interrupt my driving. Oddly though, I just drove from San Diego to Phoenix and back, and then to Irvine, without even a single symptom.

I'm going to get a MAF and maybe O2 sensors from a low mileage car at the junkyard, when I can get around to it. I've read others seem to have a low opinion of aftermarket Amazon o2 sensors, is that the consensus?

 

Went to the junkyard today. No cars with a compatible maf sensor have a readable odometer without turning the key on. i compared the resistance on the e2-tha pins on various specimens until i found one that seemed higher than what i had in the car. it wasn't much, couple hundred ohms. swapped it in the junk yard parking lot and no issues driving home. seemed a bit peppier but for whatever reason i swap a broken mirror out and the car feels like it runs better. no judgement yet. i'm planning a trip from san diego to el paso in a week so that will be a good test. i'm averaging 16.5 mpg city and about 24 highway. i feel like i could get a bit more out of it, but one thing at a time.

 

Drove from San Diego to El Paso yesterday. Was making great time except for a blew out tire in Tucson. Left 8am-ish, arrived just after midnight.

The car seems to like the newer maf, saw a couple new mpg, but the hesitation showed up almost immediately, and popped up intermittently throughout the day. Seemed to show up when the road was rough the most. Smooth parts of the road were like sailing.

Only 2 gas stops, yielding 17mpg for my "city" driving before leaving, and up to 25 mpg hwy.

No codes, I'm thinking fuel. This def has a fuel pumpy feel to it. I have the factory service manual and it's still a bit unclear where the fuel pump ecu is, I've read about that and this will be my first target.

I'm sure I'll have some downtime while I'm here in EP so I'll check out the junkyards here.

 

My 2GS had several system issues when I bought it last year. At 143k miles, it had an intake manifold gasket leak (could only find it via smoke test), gas tank valve leak (on top of tank, (low!) pressure test found it), and the multi-speed fuel pump was failing. The combination of these conditions threw many related CEL's, which I chased for months. Based on your symptoms, I would consider:

• Smoke test your intake (much more effective than spraying water/fuel). That's how I finally found the IM gasket leak. I replaced the VS Valve while I had the IM off. Might want to replace the starter motor too, if you go there.
• Smoke test your exhaust. Leaks before/at/near the O2 sensors will change the sensor values.
• Check that the rubber air intake bushing is seated onto the cast aluminum intake, and also on the plastic intake pipe end, and that the hose clamp it tightened.
• Remove your rear seat bottom (pull up the front edge, pops plastic fastener, 2X, one left, one right) so that you can hear your fuel pump while driving. It's a 3 speed pump. My pump worked, but was failing (made periodic grinding noise). The fuel pump ECU is behind the back seat upper pad (remove 4X bolts, 2 nuts behind headrest), but I wouldn't mess with it. Prepare to replace the short length of fuel tubing coming from the top of the fuel pump cover, if you kink it like I did.
• Use Torque app to monitor Short and Long Term Fuel Trims on banks 1 and 2 (that's four gauges). If the LT FT rises (positive numbers, indicates lean condition, so it's adding fuel), you may have a vacuum leak or MAF problem; maybe fuel injectors are clogged. If the LT FT sinks (is negative, indicates rich condition, reduces the FI pulse width, ie: fuel), could be a MAF problem or leaky fuel injectors (internal valve leak-thru).

After thinking about all of this, I highly suspect you need a new fuel pump (and filter, filter o-rings, pump seat o-ring, etc). One of the 3 speed circuits could be failing.

Also, is you engine/intake/exhaust stock?

 

Plastic intake pipe end? Not sure I follow, but all the hoses are totally secure, I've zip tied almost everything. Are you saying the fuel pump ecu is behind the back seat against the trunk? Not on the driver side quarter panel?
I kinda wouldn't be super surprised if the fuel pump is on the way out, the previous owner had a stack of service receipts and I don't recall seeing a fuel pump in there, so that means I'm probably still on the original one, with 280k miles.

My cheapo code reader has bluetooth, I'm assuming the torque app interfaces with the code reader? I had a better code reader that could show the fuel trims and I remember they looked odd, but I never figured out how to interpret those readings. I kinda remember a positive trim that seemed a bit excessive, but it was a while ago.

Yes, everything is stock.

I just took a short trip to a cvs maybe a mile and a half from the hotel I'm staying at and I got a couple codes P0420 and P0763. The 420 code comes and goes, I understand 763 is a trans solenoid fault. I didn't notice the car shifting any different yet, hope I can make it home, it's a 12 hour drive!

 

The plastic intake pipe end, where it meets the aluminum intake/throttle body, has a rubber gasket that fits over the plastic pipe (has a radial slit, therefore covers the inner and outer diameter of the plastic pipe), and the gasket then goes over the aluminum intake/TB pipe. This junction is located just under the on the engine cover (cover has to be removed to see it). Make sure the rubber gasket is seated all the way around, and that the hose clamp is properly tightened.

Yes, the fuel pump ECU is somewhere just behind the rear seat back on the driver's side. I see no reason to mess with it (yet).

You may gain more by lifting up the rear seat bottom on your next long drive, resting the seat bottom tipped up, and against the rear seat back. Then you can listen to your fuel pump as you drive, and possibly detect any "grinding" or changes in the rhythm. The fuel pump speed should increase as you accelerate from a stop (at engine idle).

If you've never used the Torque app on your phone, you should look into it. You also need a ($15) OBDII bluetooth module. I also have the Torque app on my android car stereo (larger screen), and the information it displays is very useful. You can watch several different ECU signals at once, all updating in real time, displayed as a moving line, needle dial, digital dial, number, and so on. You can also log signals over time and download them later, and set high and low values for your virtual gauges that will warn you if the signal reaches the set threshold (ie: coolant temp: 260 deg F!).
Google image search Torque dashboard. This information is very important for troubleshooting these problems. It may not only help you find the source of the P0420, but it will show you if you fixed it or not.

Regarding the P0763, the factory manual says, at DI-351:
Shift Solenoid "C" Electrical Malfunction (Shift Solenoid No. 3): Shifting from 1st to 5th is performed in combination with ON and OFF of the shift solenoid valves No 1, No 2, and No 3 controlled by ECM. If an open or short circuit occurs in either of the shift solenoid valves, the ECM controls the remaining normal shift solenoid valve to allow the vehicle to be operated smoothly (fail safe function).

The troubleshooting sequence calls for inspection the ECM (resistance between specified terminals and ground), the wire harness (for continuity), and then the Shift Solenoid (for resistance and making an operating noise).

The transmission may continue to operate normally without any problems, however you should get it checked out whenever convenient. It may be as simple as dropping the transmission pan (and oil!), and plugging the solenoid back in (loose plug), or replacing the solenoid. I believe the whole valve body drops down, and can be inspected and troubleshot on a workbench, and even replaced with a high performance valve body (with high performance shift solenoids?); I digress.

 

Did you ever get this figured out? It seems like a fuel pump cutting in and out would have some drag to it, like it would take a few seconds after initially feeling a loss of power til it died and maybe it could fire back up if it was quick. But more likely if it was just straight dying that would point to an electric problem somewhere. I am not quite picturing the sequence of what is happening.
Fuel trim is the increase or decrease of fuel pressure being adjusted by your upstream O2 sensor. So the engine uses air intake temp and volume is the initial value for determining how much fuel to put thru the injectors. And and then the Upstream O2 sensor can adjust it while trying to achieve a perfect 14;7-1 air fuel mixture. If it’s rich the O2 sensor will reduce the fuel. If it was running perfect all the time your Long term fuel pressure would be at 0% and then if it needs to briefly make adjustments it will register in the short term fuel trim. After a certain time or mileage or whatever the LT trim becomes the amount it’s always having to adjust it. And the short term is what it’s recently having to adjust. So if u had a leak in the intake duct after the MAF, and air was going into the intake and not being accounted for, then the O2 sensor would be adding fuel to match the extra air. Over time it will be able to measure this extra air by the amount of additional fuel. So if it had a leak that requires an additional 25% more fuel than what the MAF is calling for, over time the engine will just expect it’s going to need the extra fuel and it will account for this by recording the LT fuel trim at 25% and then the smaller adjustments that occur from elevation changes or other variables will be accounted for under the short term fuel trim. If it keeps requiring more/less short term trim then the 25% it’s already automatically adjusting it. I don’t recall the specific factors that are used to decide when it swings from ST to LT.
Hopefully I didn’t make it to confusing, I am not the best at explanations like this.

 

Drove home with little issue, although a P0420 code came up immediately. I occasionally and concerningly experienced the hesitation issue, which while intermittent, seems to be getting worse in the sense the hesitations are longer. I'm going to replace the fuel pump.

Question, denso vs walbro vs kemso? The walbro 255lph pump is on ebay for $60, while the kemso 340lph pump is $40. Seems like Denso and other "oem" pumps are even more, while the Bosch pump is $30. The Kemso seller has good feedback.

I got great mileage, btw. Going 80+ mph, got 25mpg. I spent a day cruising southern New Mexico at 50-60mph, and got over 30mpg! This car tours well =)

 

Good to hear 400gs99! Whichever fuel pump you get, make sure you get a kit that has a new filter, and o-rings. Look for the pump-tank o-ring too.

 

Spent a good amount of time today looking for a fuel pump assembly, it seems the IS300 2001-2005 are the same one ( even though on youtube the LS and RX assemblies look identical, the IS300 assembly actually is per lexus dealership info ).

Decided to pull up the back seat and have a look. The fuel pump, per the factory service manual, tests pins 4&5 at 1 ohm, within spec. I drove around for an hour or so listening, and it's quiet. I couldn't hear it clicking driving around, at idle yes, at speed no. I think
I may have noticed symptoms, sometimes it corrects instantaneously, not sure. I thought maybe I heard some grinding at one point but cannot confirm.

I'm kinda stumped. I think I'l change the fuel pump anyways because it was ******ing filthy under there, I'm sure it's still the original pump.