Gx470 Rpm Surging

[Crazymedic]

Hello all, searched for days and can't find a solution to my problem hopefully someone can help. I have an intermittent surge in RPM. Smooth idle at about 500 RPM surging randomly to 900 rpm. No AC on and nothing added or changed that would be calling for an increase. I've done the obvious air filter and cleaned the MAF sensor. I also cleaned the throttle body (removed and cleaned well) and replaced the spark plugs with iridium Denso. My initial thought was an idle air control which I planned on removing and cleaning or replacing, but I'm not seeing a traditional IACV on mine so assuming it's part of the electronic box riveted to the right side of the throttle body. Additionally I've searched for a vacuum leak using propane but found no love that route either. It runs smoothly no misses or rough idle but the random surge is just enough that if I'm at a stop light for example and am not diligent about applying the brake well it will move the vehicle forward.....I'm stumped. Thanks in advance for any advice anyone might have.

[Steve]

Hi and welcome to the Lexus Owners Club

I take it you have not had any lights on the dash?

Have you checked the air intake housing between the MAf Sensor and the engine?

If air leaks in to this then this bypasses the MAF sensor and leads to the engine getting more air than the Air Sensor is is telling the ECU.

Hope that makes sense.

Just check for cracks or loose parts.. slightest crack can cause surging.

[Crazymedic]

Thanks for the reply. No dash lights and everything is tight without cracks or defects. I had it all apart from air filter to the throttle body cleaned and inspected it Found nothing. I also used propane to check for leaks assuming I will get a response with any kind of Crack or loose seal on the entire intake. Again, nothing. Also, when I did spark plugs and the initial throttle body cleaning I disconnected the neg bat terminal so the ecu would reset everything when I was done. Made no difference.

[mn83985]

I have the same issue. This surge in RPM happens to me occasionally when I am stopped at traffic lights or drive thrus! Its not a crazy acceleration but enough to make sure you apply enough brake pressure to keep from rolling into the car in front of you. I believe this is an issue with the torque converter possibly