Noise From Throttle Control Motor?

snx37 · August 25, 2011

'99 GS300, 97K miles.

For the past 2 days, after the car has been on the road for 15 minutes or so, the acceleration begins to lag. At first it becomes unresponsive to small pedal inputs, then eventually it is necessary to push the pedal to the floor to get any acceleration at all. Check engine, VSC and VSC OFF lights come on.

From what I've read here and in the manual, it sounds like there's a problem with the electronic throttle control system. I have checked the resistance on the throttle position sensor, pedal position sensor and throttle control motor. All check out OK. (The throttle control motor was .1 ohm high, but it was also above the temperature specified for the test. It dropped down to the highest allowable reading, once it cooled off.)

The manual also calls for operating the pedal position sensor (with the ignition on / engine off) and listening for the operation of the throttle control motor. It does operate when the PPS is moved, but there is also a continuous high pitched buzzing from the throttle control motor when the ignition is on (even when the PPS is not operated.)

Is this noise normal? I've never listened closely under the hood with the ignition on and the engine off.

I suspect the problem is one of the two sensors or the throttle control motor, but I don't want to start simply throwing parts at the problem!

If anyone has any other insights, they would be appreciated! (The one other test I have done is turning the AC on and off at idle. The manual says the RPMs should rise from 700 to 750 with the AC on, but they actually drop a little.)

Thanks in advance!

1990LS400 · August 25, 2011

As you are finding, the TPS and/or PPS can fail erratically and gradually. Works sometimes, doesn't work other times. Mine (on my 2000 LS400) failed gradually in 2008 at a bit over 100,000 miles. I don't remember mine making a noise when it was failing. I was mainly glad to limp the car home and then to a repair shop.

snx37 · August 26, 2011

As you are finding, the TPS and/or PPS can fail erratically and gradually. Works sometimes, doesn't work other times. Mine (on my 2000 LS400) failed gradually in 2008 at a bit over 100,000 miles. I don't remember mine making a noise when it was failing. I was mainly glad to limp the car home and then to a repair shop.

Yes, I've been doing a bit of reading, and it seems to be a very common problem. Unfortunately it also seems that it could be any one of the three components on the throttle body, and none of them are cheap... It doesn't make sense to try and fix it by throwing parts at it.

I wish I had spent some time listening to my throttle control motor, so I would know if the noise is normal or not.... or if only I had a known good one to listen to!

If anyone knows whether that noise is normal or not, it would be a great help.

Thanks!