Since I had the intake tube off yesterday while changing out the spark plugs, I decided to go ahead and clean the throttle body/butterfly. I used CRC cleaner and went to town, being careful not to tweek the butterfly, etc. Got a good amount of black buildup out of there.

My question is regarding the idle speed. Is it normal that the engine will run at a higher idle speed for a while after cleaning the intake path? It initially ran at around 1,000 RPM or so yesterday and this morning, but has now settled back to its normal 750 RPM or so. Should I have simply disconnected the battery for a few minutes following this?

We have also had a few days of weather in the low teens, but that would not explain the high idle after some extended driving.

Again, all seems well now, but I'm cuious what may have caused this temporary jump in idle speed.

Andreas

 

Fishing for your thoughts...

Andreas

 

I have had the same thing happen on the Runner and other vehicles after a TB cleaning. Do I know the physics behind why it happens? No. But, I can tell you that all the vehicles are alive and kickin to this day.

 

As far as I am aware it is caused by the ECU adjusting idle (there is no idle screw on a 3rd gen......so the ECU uses the Idle Air Adjustment valve, located just under the throttle body to compensate for the slight restriction the carbon buildup has created) for a certain amount of airflow at idle which is allowed to pass by the butterfly plate. When you clean the throttle body and remove the carbon buildup that has accumulated, you are now removing a tiny bit of restriction that was there. So now when you start up the truck, the ECU needs time to readjust to the new amount of airflow, realize this is now a permanent change and move the IAC into the proper position to maintain 750 rpm with this new air flow rate.

Very technical I know, but I hope it helps.

 

Jamie,
That's exactly what I thought may be happening. Not too technical at all. Thank you.

Andreas