UMD GS400 Posted July 20, 2005 Share Posted July 20, 2005 Recently my 99 GS 400 stopped accelerating while I was cruising at 65 mph. The check engine light came on as well as the VSC indicator and VSC OFF indicator. After pulling off to the side of the rode in the middle of the night, I turned the car off a couple of times and tried to drive off with no luck. On the third try the trouble lights were still illuminated, however, I was able to accelerate at this point. Upon reaching 2 miles from home, the car failed to accelerate once more and I was reduced to driving 5mph the rest of the way home. The next morning I drove the car to the dealership for service hoping I would not experience the same problems because the indicators were still present. The dealership diagnostic indicated there was trouble initially with the throttle position sensor, then the dealer explained I needed a new throttle body replacement. Total cost to yours truly $1200. Does anyone know why it is not possible to clean the throttle body to reduce the sticking of the butterfly? What else can be done to avoid this $1200 rape?? All input is welcome. Quote Link to comment Share on other sites More sharing options...
indiasfinest Posted July 20, 2005 Share Posted July 20, 2005 i wish i could help srry man Quote Link to comment Share on other sites More sharing options...
GuyTelefunken Posted July 20, 2005 Share Posted July 20, 2005 It is most likely a problem with a position sensor, motor, or the electromagnetic clutch within the throttle body. Look for a used one on Ebay or at a salvage yard. You can buy the part Here for $740.44. You should also replace the throttle body gasket as well. Installation involves draining some coolant, removing the throttle body, installing, refilling coolant and bleeding, then clearing any codes from the computer. Quote Link to comment Share on other sites More sharing options...
new big400 Posted July 20, 2005 Share Posted July 20, 2005 Do some shopping around if you do truely need a tb.Did they say what was wrong with your throttle body?I know there seems to be alot of probs with the tps and the dealer always seems eager to replace the whole tb.I dont know if theres a reason for this or of theyre just makin$$.Id ask why you cant just try a tps if there is nothing else wrong with your tb.Please keep us posted as I have a 98 gs4 and Im just waiting for this prob.to happen. Quote Link to comment Share on other sites More sharing options...
UMD GS400 Posted July 20, 2005 Author Share Posted July 20, 2005 It is most likely a problem with a position sensor, motor, or the electromagnetic clutch within the throttle body. Look for a used one on Ebay or at a salvage yard.You can buy the part Here for $740.44. You should also replace the throttle body gasket as well. Installation involves draining some coolant, removing the throttle body, installing, refilling coolant and bleeding, then clearing any codes from the computer. ← The dealer said the throttle body was sticking and there was no cleaning or repair maintenance that could be performed. I just don't understand how this could be, but I guess the warning signs were there and I just didn't realize. The car had stalled on rare occasions, but nothing a turn of the key didn't solve. The problem went from minor annoyance to major pocket hit $$. I'll keep you posted if I find any cheaper alternative, but something is telling me that is not going to happen. Quote Link to comment Share on other sites More sharing options...
UMD GS400 Posted July 20, 2005 Author Share Posted July 20, 2005 It is most likely a problem with a position sensor, motor, or the electromagnetic clutch within the throttle body. Look for a used one on Ebay or at a salvage yard.You can buy the part Here for $740.44. You should also replace the throttle body gasket as well. Installation involves draining some coolant, removing the throttle body, installing, refilling coolant and bleeding, then clearing any codes from the computer. ← Thanks for the link. Wow, this is an expensive part and it's not even an upgrade. Quote Link to comment Share on other sites More sharing options...
TurboGS300 Posted July 20, 2005 Share Posted July 20, 2005 Earlier I wrote re a problem w/ loss of acceleration on my '98 GS300. The CEL & VSC lites came on & it went into limp mode. Auto Zone read the codes as a throttle position sensor (P1120 & P1121) which I then had replaced at my local Toyota dealer for $160 parts & labor. Ran great for 2 wks...then problem recurred. Took it back to Toyota & they said it needed a whole new throttle body...to the tune of $1200. (They said it showed same codes as before. Didn't have an explanation for that..) Decided to go back to the local indie Lexus shop I used for my '92 ES, Davenport Motors in Plano, TX. Good people there... should have gone there first. Took a day & $500 but they fixed it...said they had never replaced a throttle body on a GS. They'd seen this problem before... faulty pedal position sensor. Car even seems a touch zippier now...maybe just happy not to be limping Also, sensor Quote Link to comment Share on other sites More sharing options...
UMD GS400 Posted July 20, 2005 Author Share Posted July 20, 2005 Earlier I wrote re a problem w/ loss of acceleration on my '98 GS300. The CEL & VSC lites came on & it went into limp mode. Auto Zone read the codes as a throttle position sensor (P1120 & P1121) which I then had replaced at my local Toyota dealer for $160 parts & labor. Ran great for 2 wks...then problem recurred. Took it back to Toyota & they said it needed a whole new throttle body...to the tune of $1200. (They said it showed same codes as before. Didn't have an explanation for that..) Decided to go back to the local indie Lexus shop I used for my '92 ES, Davenport Motors in Plano, TX. Good people there... should have gone there first. Took a day & $500 but they fixed it...said they had never replaced a throttle body on a GS. They'd seen this problem before... faulty pedal position sensor. Car even seems a touch zippier now...maybe just happy not to be limping Also, sensor ← You definately sound like you were experiencing the same problem as me. What is the difference between the throttle position sensor and the pedal position sensor? They sound similar to me? Have you had any problems since? Quote Link to comment Share on other sites More sharing options...
TurboGS300 Posted July 20, 2005 Share Posted July 20, 2005 It seems to be a rare, however common problem, the quote was from member MDCRABCAKE with a similar problem. I'm betting the Pedal position sensor is on the throttle pedal. . <_< Quote Link to comment Share on other sites More sharing options...
new big400 Posted July 20, 2005 Share Posted July 20, 2005 What exactly was happening that caused you to go to the dealer?This sure sounds like a tps or pps.Im not sure whrer your pps is but I was under the impression it was part of the tb.Not sure though.I think my car is developing the same prob. Quote Link to comment Share on other sites More sharing options...
TurboGS300 Posted July 20, 2005 Share Posted July 20, 2005 Alot of newer vehicles no longer use a "cable" to connect the accelerator to the throttle body. It's all connected by wires. A faulty PPS would cause the car to behave erratically when concerning throttle. Look at the accelerator pedal near the top or middle and see if you see any wires. Quote Link to comment Share on other sites More sharing options...
new big400 Posted July 20, 2005 Share Posted July 20, 2005 I know this has been argued back and forth alot and really wont help much in this case but is just a bit of usefull info.The guys at SRT told me a gs4 was drive by wire and also had a back-up throttle cable in case of a system failure. Quote Link to comment Share on other sites More sharing options...
GuyTelefunken Posted July 20, 2005 Share Posted July 20, 2005 I know this has been argued back and forth alot and really wont help much in this case but is just a bit of usefull info.The guys at SRT told me a gs4 was drive by wire and also had a back-up throttle cable in case of a system failure. ← They were correct. The throttle cable controls the Pedal Position Sensor on the throttle body. The signal from the PPS goes to the ECU. THe ECU determins how much to move the throttle motor to open the throttle. The amount of opening is reported back to the ECU via the Throttle Position Sensor. There is a electromagnetic clutch between the PPS and the throttle butterfly. If there is a problem or descrepency between the sensors the ECU commands the throttle motor off and engages the clutch to provide conventional, cable-operation of the throttle valve. Quote Link to comment Share on other sites More sharing options...
TurboGS300 Posted July 21, 2005 Share Posted July 21, 2005 So guy if there's a problem with the PPS and the TPS, the electromagnetic clutch may not kick in and you'd get a problem similar to the one UMD GS400 described. I'd call davenport motors in TX and ask them exactly what needs to be replaced, as it sounds like they're only replacing the PPS. Quote Link to comment Share on other sites More sharing options...
GuyTelefunken Posted July 21, 2005 Share Posted July 21, 2005 If there's a problem with the PPS and/or the TPS the clutch would be engaged. This is the purpose of the clutch; to engage when any fault is detected that may impeed proper acceleration or speed control. The MIL (Check Engine), VSC, and VSC Off light would illuminate. The clutch is a very rare item to fail since it is virtually never engaged during the life of the car. Note: The reason the VSC indicators illuminate is due to the fact that the VSC system cannot operate without electrical control of the throttle. In mechanically-linked mode, VSC operation would not be possible. The way I read the original post is as follows: There is a mechanical reason that the throttle butterfly is sticking. It may be crud in the throttle body, corosion on the butterfly shaft, wear in the throttle motor or valve drive geartrain. Something mechanical is causing the TPS to vary from the expected position the ECU is looking for via the input from the PPS. As each component, motor, sensor, valve, etc. is dependent on one another, it is difficult to ascertain which component is the root cause of the problem. If you were very familiar with the throttle body assembly, it could be taken apart and closely examined to narrow down the exact cause. Certain components of the throttle body assembly are available as replacement parts, most are not. Keep in mind, whenever the throttle body is dissassembled it must be realigned (calibrated) electrically with a scantool. It's not difficult but it is necessary for proper operation. The Lexus garage most likely wishes to err on the safe side and replace it all as a unit. If there was a code that specifically pointed to the PPS or TPS, I would think they would have recommended replacement of that component only. Each garage has their own work ethic. Lexus generally wants to get the job done right the first time. Replacing one component at a time is not always the most effective way to do that. It would be interesting to me to know exactly which codes were in the ECU the first time this problem was diagnosed. Quote Link to comment Share on other sites More sharing options...
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