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Today I noticed something annoying on my 01 UL LS430, The RPM rate drops to around 500 when I set the transmission to "D" along with a slight vibration and strangely. If i change that to P, N. or even Reverse. It jumps back to 700 normally. Above numbers are while no AC/Headlights on. If i turn on the AC, the headlights or the seat heater. those 500 jumps to 700.

What I tried so far:

  1. Cleaned Air filter, MAF, Throttle body and those throttle upper tiny holes (dunno their name).
  2. Spark Plugs are brand new, didn't even reach 20.000 km yet.
  3. Hooked up an OBD2 comprehensive tester and it showed absolutely nothing wrong.
  4. Un-plugged the MAF sensor while the car is idling and it immediately shut off (Saw it somewhere, that this can determine if the MAF sensor is working or not).

Any suggestions?

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    Welcome to Motor Vehicle Maintenance & Repair! – Pᴀᴜʟsᴛᴇʀ2 Aug 22 '18 at 0:08
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    Welcome. How many miles are on your LS? – Nick Aug 22 '18 at 15:20
  • 127.000 miles so far – Mohamed Hussien Aug 23 '18 at 0:44
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Hello fellow LS 430 driver. My car also drops to "around" 500 RPM. It's actually 600 RPM when in drive. It does not shake though. If the idle air valve (or whatever Toyota calls it) is broken (at least, in a way the ECU can detect) you would get an OBD code. So, ignore the RPM difference for the moment.

Check the motor mounts for wear -- a broken motor mount will cause the shakes.

With modern cars (and especially Lexuses) most electrical issues related to the engine will be reported via the OBD system. But, other mechanical issues could occur that will cause issues that cannot be sensed by the ECU.

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  • Thanks Nick, Really appreciate it. I got your point. So fixing the mounts will make that issue (if it really is) less noticable by removing the vibration. – Mohamed Hussien Aug 23 '18 at 0:48
  • No problem -- yeah I would check the mounts before doing anything else. Just hit 190,000 miles on my LS. Good luck. – Nick Aug 23 '18 at 1:52
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Did you really clean that throttle body shutter. They can be stubborn, and even a slight dirt ring on the back can interfere with air intake. The fact that your idle jumps when your IAC valve is activated suggests the throttle plate.

The next most likely culprit is the PCV valve (which can be seen here).

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  • Not sure really, maybe it needs another go of cleaning. I'll check that out during the weekend – Mohamed Hussien Aug 23 '18 at 0:48

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