ill take a look when i get out of work and let everyone know. thank you for the help. Im going with your logic and i assume it would be the same part. its the same engine. the only difference is the 6 speed trany which i seriously doubt would change the TPS. I'll keep everyone posted.

 

The 6-speed tranny is in the 2004 model year too, so it's not really a difference.

Rough idle can be caused by clogged fuel injectors too, but I assume you're confident that the gas treatment you put in last June resolved that possibility. The acceleration symptom you described strongly suggests TPS. Odd acceleration doesn't typically occur with clogged fuel injectors.

 

Well it's raining so I didn't pull the engine cover off to look at the TPS physically, but I did hook the code reader up and let the car idle for a while. I believe you nailed it. Thank you. I graphed the absolute throttle position which as far as I know would be the reading the TPS is reporting. With everything off. Engine idling. No air conditioning, no seat heater, no lights. The tps slowly jumps between 14.1% and 14.5% the idle is smooth. Then it starts jumping between 14.1 and 14.5 quickly (several times in a second) and the idle goes to crap. It's definitely not the computer making a throttle adjustment because with the engine off and key on it see the same thing happening. I took readings while the car was cold and it showed 14.5% constantly. It didn't show 14.1 until it warmed up and sat for a while. So I'm going to go ahead and say it most likely is the TPS.

 

Well... Christmas eve, visiting dad. Ah let's take a look under the engine cover... and the reason the throttle position sensor only fits 01-04.... there isn't one. Son*@&$*%?! Left hand side of the throttle body is the actuator which must have position feedback built in because on the right hand side where the sensor would be is a brass cap plugging the hole where the stem attached to the butterfly flap would come throguh. So the dealer wasn't bs'ing me. Why in the world they would make the change and do away with it is beyond me, but now what? I guess it is time to have a fog test done to look for vacuum leaks. And I guess I'll do a set of plugs too. Heck I just hate throwing random money at it unless I feel pretty sure it's going to help. Part that scares me, if it is the "TPS" I guess I'll have to replace the whole throttle body :-/

 

Rather than throwing parts hoping for a random solution, get it professionally diagnosed, then fix it yourself.

 

I agree that will probably be my end solution, but I was hoping for a miracle. thinking maybe if im specific enough with my symptoms, someone on here would recognize them and go "ah ha mine did the same thing and it was ___"


as a last ditch effort to have that happen I have one last symptom. I left my in-laws house last night. its a 100 mile drive home. the first 35 miles of the drive the car drove like it was brand new, all kinds of power climbing hills like no ones business. real time gas mileage was showing low 20s on inclines and upper 20s- low 30s on level road. the car never ran so well. we made a 10 minute pit stop for the wife to run to the rest room. and upon restarting the rough idle was there and it drove the last 65 miles like a dog, lacking power, shifting rough just like I've been complaining about. gas mileage on similar inclines were now low teens or single digits and the highest I got was 23 on a straight a way. even driving down hill slightly it only registered low 30's. and felt like something was holding it back. so whatever is going on is made much much worse by re starting the car while it's warm.

 

Took a gamble and replaced the MAF. idles like silk. Runs like a raped ape. I'll give another report in a week. After I put it in I had to turn off "power mode" because it was so jumpy. Hopefully gas mileage goes up. The only difference I noticed between the old and new sensor is how fast it reads
Even after cleaning the old one it was sluggish compared to this one.

 

Hopefully congratulations are in order, my3uzfe!

I had the exact same issues with my 1990 LS400 and my 2001 LS430. In both cases the Fuel Pump Resistor ( PN: 23080-50090 and available for $60.44 from Lexus of South Atlanta here ) was faulty. I don't recall what the measurement was precisely on my LS400 (I did that a couple years ago), but my LS430 resistor was testing THREE times the resistance at 68°F (1.1 Ω vs .30 - .34 Ω (point-three-zero to point-three-four Ohms)). As the temperature goes up, resistance goes up as well and the engine gets starved for fuel at part-throttle. This might explain why in your case, like mine, you sometimes get great performance, turn the car off for a bit, go to drive it again while it's still hot and get terrible performance and mileage.

If it weren't for the fact that I had discovered it on my LS400 and learned how to test it, I might have fallen into that trap we all do at some point, especially early on, and thrown parts at it out of sheer irritation until fixed! And as we all know very well by now the Lexus mantra 'Pursuit of Perfection' of their Profit Margins with the "What can we build for a Yen and charge the customer ten?" business model; or my all-time favorite, the "You can't get that one, single part you need without buying ten other parts you don't need because it's an 'assembly'" excuse... Seriously, take the cost of any OEM Lexus replacement part such as the fuel pump resistor ($60.44) and divide it by ten ($6.04) and you will just know that is more likely the total cost to produce the damn thing. $1.45 for a plastic clip? I don't think so. More likely 14.5 cents once you figure in research and development, tooling, materials, labor, advertising... Honestly, it's a wonder my Lexus parts department hasn't given me a stroke or two over the years. Any sensor installed in a high temperature environment should automatically be suspect after a few years anyway and tested in due course just to be sure it is functioning properly. Common failure items employing heat-sensitive components are mass air flow sensors, ETC sensors, ambient temperature sensors, ECU's, the ubiquitous fuel pump resistor...you name it. This applies to all modern electronics in high heat applications, as well. It's just logical reasoning based on the preponderance of the evidence. just look at how many models on this site alone are having the same exact problems we've had, and Toyota has been using fuel pump resistors and the like on nearly every fuel injected model going back to 1985. Anyway, I just might have the cure for what ails your baby, and saves you a whole lot of frustration and money! I'll even give you and future generations the Lexus factory repair manual documents for reference.

1. Take the engine bay cover in front of the master cylinder off and look for an aluminum "heat sink" with two wires coming out of it.

2. Notice the end of it will be stamped with the part number and an Ohm (Ω) value. Unless the temperature of the resistor is 68°F, take it off the car and either warm or cool it before testing with a multimeter. It should register between 0.30 − 0.34 Ω at 20°C (68°F). If it doesn't, replace it and reset your ECU. Simple as that! The resistance will just get worse with age and the hotter it gets sitting under that pretty plastic heat trap.

Now, you can test whether this will actually solve your problems before buying it with the method I have used on both my LS's and simply bypass the onerous thing with a jumper wire. Just unplug it at the clip and insert a small gauge shielded jumper wire, (not a paper clip unless it's wrapped in electrical tape) such as a short piece of electrical wire with each end stripped, insert it into the female sides of the connector and go for a drive. You might even do as I did and drive it that way for a few days, letting the computer relearn, just to be sure. I created a bypass from cutting the wires about two inches past the clip joint of the resistor itself and soldered/heat shrink tubed them together on my 1990 LS400 and have been driving it like this for over two years now with no ill effects whatsoever. After all, we're talking about taking a negligible .30 Ohm spec load down to a naught ohm load. But keep in mind that as asinine a part as it is, it does serve a function (albeit a marginal one in my humble opinion), and theoretically allows for longer fuel pump life by throttling, or governing the pump to a lower voltage draw and therefore lower speed and volume when demand isn't required, i,e, part-throttle cruising (Toyota's explanation for it...personally I think it's pre-planned obsolescence). This usually isn't a problem unless you are climbing slight inclines, maintaining speed on inclines, or otherwise accelerating at less-than-full throttle (to the ECU's interpretation, anyway) and experience a lack of power, indecisive ETC shifting, poor mileage, rough idle, and poor emissions to boot!

So, in my final analysis I deem the thing practically useless myself, but replaced it anyway while my local Lexus parts people most likely cursed me as I walked out the door with the cheap solution to what otherwise might have been a reason for them to celebrate my predicament by piece-meal-selling me a whole new fuel system, as an 'assembly', of course! It's probably one of the three main sensor fixes they typically do to trade-in's with similar symptoms before reselling it after the owner was most likely quoted some outlandish amount like $10,000 to rebuild their car's entire fuel and emissions systems to force them to 'trade up'. Please do yourself a favor and test your fuel pump resistor before doing anything else or buying any more parts. You seem to have covered all the bases anyway, but if this does not fix your problems I will be more than happy to assist you further with whatever help and documents I can provide. Good luck, and please keep us all updated, especially for posterity!

LS430 Fuel Pump Resistor Diagram.pdf

LS430 Fuel Pump Resistor Test Procedure.pdf

 

MRLexus90, that is some great information! I, like you, try to diagnose problems till I know for sure that the part or parts I'm buying will likely fix the problem. It gets very frustrating at times but when you take the time and have the resources to diagnose a pesky problem, there is great satisfaction in knowing that you didn't just waste a lot of money throwing parts at at it. Could you get lucky and buy the right part the first time, sure, especially if you research great forums like this because so many may have had the same issue and have proved that a particular fix does truly work.

So many shops now are parts swappers until one of them fixes the issue. Or in many cases they swap a bunch of parts and it still doesn't fix the issue, then they start to diagnose the problem only to find the parts they just changed didn't need to be done in the first place but it doesn't matter to them. Usually the customer is happy for the most part as long as the issue is fixed but they unknowingly just spent a lot of money on parts and labor that weren't needed at all. From my personal experience, this comes from owners trying to save money on labor with the hiring people that aren't qualified or capable to diagnose problems. They rely on scanners and other avenues (alldata, etc.) to find the likely fixes and swap parts. I'm not saying those aren't great and useful tools. They should definitely be used and many of them are very accurate in pinpointing what may need to be replaced. The problem lies when the parts swapper doesn't even fully know what the part he's changing really does and may not be able to think to themselves that maybe this isn't the right part to change due to the symptoms the car is having.

I'm not in any way faulting anyone who for whatever reason cant or doesn't want to work on their own cars. For many people, that's a good thing. I consider myself very lucky that my dad, although he worked in an office job and wasn't a mechanic, a carpenter, plumber, electrician, etc., taught me to not be afraid to get your hands dirty and learn how to fix things yourself and not be afraid to fail. I'm following in those footsteps myself. Not because I couldn't afford to have someone do it for me. But as long as I have the time, tools, resources, etc., why shouldn't I? It's almost a form of therapy for me.

Undoubtedly ten of thousands of dollars (or more) have been saved by the members by doing research on this great forum. Thank you to the many members on here that take the time to share their knowledge to help others.

my3uzfe, I hope your problem is finally solved!!!

Have a Happy New Year!

 

I know this is an old thread, but trying to solve a Code PO115 problem. Is changing the "engine temp sensor" the same as changing the engine coolant sensor?
I wish I got such great mileage! .... mine usually shows getting 16-18 mpg around the neighborhood - I don't do long distance driving. I have 94K miles on an 01 LS430 UL.

 

Yes it's the same thing.

 

My 04 LS430 has the opposite problem. With the AC off the engine idles rough at 400 rpm and with the AC on the engine idles smoothly at 600 rpm. My car has 171km. The motor feels smooth and strong during normal driving. I recently took care of a lot of codes that came up. Cleaning the MAF and throttle body took care of #101, #103 and #104. Found 5 of 8 coil modules had cracks on them. All even bank modules and number one were found to have cracks. 2 of the coil modules had cracked the full length of the unit. After replacing all coil modules code #300 was taken care off. I also replaced the breather pipe and PCV pipe as well. Drove the car for a week and no other code came up. Now the engine has this rough idle problem with no detectable codes.

 

Massive thread resurrection.

I have the same issue as described above. Did anyone get to the bottom of it?

I have:
- new spark plugs
- changed coils
- cleaned MAF and TB
- Replaced Vac hoses
- checked the brittle plugs
- run a full scan with TechStream, no codes.

Appreciate any help.
-

 

I don't know how much it affects idle, but there's a chance that your VSV for the ACIS no longer functions. When the VSV no longer functions it vents to atmosphere which will create a small vacuum leak. This requires removing the intake to get to. I would put this only as last.
My intermittent misfire/stumble at idle was due to a coil pack going bad. It would only misfire sometimes and not enough to trigger codes or even enough to get it to save long term codes. I had to actively watch the misfire counters to catch it.

​​​​​

​

 

what mileage are you at? I changed my motor and transmission mounts and things got really smooth in the powertrain. I did mine at 220k miles but probably needed it a LOT sooner, maybe even after 150k.