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98 Ls 300 Accelerator Position Sensor Fix


fjstl
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the check engine light came on to my 98 LS 400 with 115K. My dealer said it was a bad accelerator position sensor. I had them change it along with a new battery. The cost to install and replace the sensor was around $525 and the battery was 175. The price was high but I had nowhere else to go for the repair. Prior to bringing in the car for repair it idled in neurtral at about 650rpm's when warm. It now idles around 980 when warm. I advised the dealer of this and they checked it again on their equipment and then advised me that it was within specs for a car this old and with 115K. They also said that there weren't any other adjustments that could be made to lower the rpm's. I'm afraid this could damage the transmission. Any suggestions?

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It now idles around 980 when warm. I advised the dealer of this and they checked it again on their equipment and then advised me that it was within specs for a car this old and with 115K. They also said that there weren't any other adjustments that could be made to lower the rpm's. I'm afraid this could damage the transmission. Any suggestions?

Hmmmm, the factory specs for the car actually say Idle speed (Transmission in neutral, all loads off, No A/C): 750 ± 50 rpm. Your transmission will be fine even at the higher idle, but the cause for concern is them not knowing any better. My $10 says they have not set it in the correct position, as per the attached PDF file. Take it back to them and say the power of the internet is on your side!

The technical background is ;

The 98 year was the first to incoporate the electrically controlled throttle. The idle speed is controlled by the Electric Throttle Control System (ETCS).

ETCS is composed of the throttle motor to operate the throttle valve, the magnetic clutch to connect the

throttle motor with the throttle valve, the throttle position sensor to detect the opening angle of the throttle

valve, the accelerator pedal position sensor to detect the accelerator pedal position, the ECM to control the

ETCS and the one valve type throttle body.

The ECM controls the throttle motor to make the throttle valve opening angle properly for the target idle speed.

If the accelerator position sensor is not set correctly the car will be given a false position. Not much, but probably enough to raise you idle rpm.

Hope this sorts it.

SF_42_Throttle_position_sensor.pdf

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Sounds like you took it to the local dealership around my parts! :blushing: haha Why is it that these dealerships that charge an arm and a leg for service and repairs don't know anything about what they're doing, and DON'T care either! It's ridiculous! anyways back on topic.... my 97 LS400 when warming idles around 1400RPM and when warmed idles around 800RPM are the idling stats for the 98 the same as 97??

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It now idles around 980 when warm. I advised the dealer of this and they checked it again on their equipment and then advised me that it was within specs for a car this old and with 115K. They also said that there weren't any other adjustments that could be made to lower the rpm's. I'm afraid this could damage the transmission. Any suggestions?

Hmmmm, the factory specs for the car actually say Idle speed (Transmission in neutral, all loads off, No A/C): 750 ± 50 rpm. Your transmission will be fine even at the higher idle, but the cause for concern is them not knowing any better. My $10 says they have not set it in the correct position, as per the attached PDF file. Take it back to them and say the power of the internet is on your side!

The technical background is ;

The 98 year was the first to incoporate the electrically controlled throttle. The idle speed is controlled by the Electric Throttle Control System (ETCS).

ETCS is composed of the throttle motor to operate the throttle valve, the magnetic clutch to connect the

throttle motor with the throttle valve, the throttle position sensor to detect the opening angle of the throttle

valve, the accelerator pedal position sensor to detect the accelerator pedal position, the ECM to control the

ETCS and the one valve type throttle body.

The ECM controls the throttle motor to make the throttle valve opening angle properly for the target idle speed.

If the accelerator position sensor is not set correctly the car will be given a false position. Not much, but probably enough to raise you idle rpm.

Hope this sorts it.

thanks for the reply and I'll go with your suggestion. thanks again

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I don't know how much difference there is between the idle control of your 98 and that of my 96....but adjusting the idle on mine is not possible by tweaking the throttle position sensor. It is more a matter of controlling manifold pressure thru use of an idle air valve.

Check the vacuum hose connections to your intake manifold. I had a broken hose going down to the power steering pump idle-up valve which cause an abnormal idle in mine. The hose was brittle with age and had cracked at the barb fitting.

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  • 4 weeks later...

My 98 LS is finally fixed. When I mentioned about the suggestions from this group on the web I was advised to drop it off and it would be fixed once and for all. They cleaned the throttle body and what a difference this made. The idle is now about 730 and it runs fantastic for a car with 115K on it. The mpg has also improved from about 26 on the hiway to about 28.

Thanks for the suggestions.

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My 98 LS is finally fixed. When I mentioned about the suggestions from this group on the web I was advised to drop it off and it would be fixed once and for all. They cleaned the throttle body and what a difference this made. The idle is now about 730 and it runs fantastic for a car with 115K on it. The mpg has also improved from about 26 on the hiway to about 28.

Thanks for the suggestions.

Just another example of the power of LOC!

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