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High Idle Speed After Engine Is Warm


James925
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I just bought a 1990 LS400 with 89k miles and it's very clean. I have 2 problems though. The first is the idle speed whem warm. Most of the time the idle speed is about 1100-1200 whem warm and only sometimes will drop all the way to a normal 700-650. I have been looking at different postings and have cleaned my IAC and have replaced and adjusted my TPS. After cleaning the IAC no change was noticed. After changing the TPS it idled normal at 650 but after the engine cooled down and I started it it would only go down to 1100 agian. Could it be a bad water temp sensor? The second is when I'm driving with the overdrive off around town at about 35-45mph and take my foot off the accelerator pedal the car will slow down as if it was a manual transmission and in gear. It only does this sometimes. Is it because the torq converter is locked up causing engine braking? Any help for either problem would be greatly appreciated. I'm trying to find a factory service manual to find out more info.

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After changing the TPS it idled normal at 650 but after the engine cooled down and I started it it would only go down to 1100 agian. Could it be a bad water temp sensor?

Could be a the temp sensor or a dirty ISC valve.

The second is when I'm driving with the overdrive off around town at about 35-45mph and take my foot off the accelerator pedal the car will slow down as if it was a manual transmission and in gear. It only does this sometimes. Is it because the torq converter is locked up causing engine braking? Any help for either problem would be greatly appreciated. I'm trying to find a factory service manual to find out more info.

Lookup NC's posts. In one of them, if I can recall correctly, he mentions something about off throttle shock creating reverse torque. I didn't bookmark the post, but I did download the Toyota TSB for this. You'll find it here:

http://us.lexusownersclub.com/forums/index...ost&id=8682

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After changing the TPS it idled normal at 650 but after the engine cooled down and I started it it would only go down to 1100 agian. Could it be a bad water temp sensor?

Could be a the temp sensor or a dirty ISC valve.

The second is when I'm driving with the overdrive off around town at about 35-45mph and take my foot off the accelerator pedal the car will slow down as if it was a manual transmission and in gear. It only does this sometimes. Is it because the torq converter is locked up causing engine braking? Any help for either problem would be greatly appreciated. I'm trying to find a factory service manual to find out more info.

Lookup NC's posts. In one of them, if I can recall correctly, he mentions something about off throttle shock creating reverse torque. I didn't bookmark the post, but I did download the Toyota TSB for this. You'll find it here:

http://us.lexusownersclub.com/forums/index...ost&id=8682

Thanks for the info I think I'll replace the temp sensor. But, I guess there are two temp sensors. One I think is a temp sendor and the other is the temp sensor not to sure which one tells the ECU when it's warm or cold. I think it's the temp sender. not sure.

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