Motorheadno13

I've been having a strange problem with my 4Runner since all the rain hit southern California. First off, the truck idle's at about 2000rpms on a cold start. If I give the throttle a good blip during this time, it will bog out and blow a black puff of smoke out the rear. It seems like a rich bog actually. Also, there is an itermittent problem with the heater blowing cool air when it's set on the 4th speed, this is after the truck is at operating temperatur; but only happens on the 4th speed. This only happend to me once but it did happen. When the truck is warmed up everything feels ok. However, the temp gauge constantly fluctuates from center to the edge of temp sign whether I'm on the throttle or not.

I was thinking it could be the auxilary air valve, afm, thermostat, or coolant temp sensor. Then I thought maybe its the water pump or some kind of vacuum leak. Could it possibly be the tps sensor, or maybe even something as simple as low coolant. I do know the water pump, thermostat, O2 sensor and a bunch of other parts were replaced when the motor was rebuilt in 2003. I'm going to check the AAV and the coolant level here in a few minutes.

MudHippy

Yeah, make sure the coolant level isn't low. And from the list of things you mentioned, my gut feeling is the coolant temp sensor. When mine went out it acted in a similar fashion. Yes, I said sensor, not sender. And why the temp gauge went haywire when the temp sensor was bad and not the temp sender is beyond me, but it did.

Motorheadno13

Ok, I had to add about 3/4 of gallon to the radiator, so that could be the issue. It's possible that coolant wasn't making it's way up to the auxilary air valve and closing it. The truck wasn't fully cooled but I tried to test the AAV afterwards. I took a pair of flat nose pliers and pinched the coolant hose going in to the throttle body to check for a change in idle but nothing happend. So I'm assuming the AAV is fine? I'll test it again when it's fully cooled.

Motorheadno13

Just for reference in case someone has similar issues, the problem was solved:

It seems like the issue turned out to be the auxilary air valve. Its located in the throttle body with a coolant line feeding it. When the motor is cold, the AAV stays open keeping the engine idle high to help warm up the engine. When the motor gets to operating temperatures, the hot coolant causes the AAV to close therefore droping the idle. I added about a gallon of coolant, which means there probably wasnt any coolant reaching the AAV to properly close it when the motor is warmed. The low coolant level also answers the question for a fluctuating temperature gauge.

I had no idea being low on coolant would cause all this... From what I understand, the AAV on newer vehicles are electronically controlled.