High rpm on startup

[bryris]

4.0 motor, 2006 EB.

On a cold start, it'll idle about 1,500rpm or so for about 2 minutes. If I put into gear it'll behave normally. If I let it idle, after the two minutes it'll slowly drop down to regular idle. Intermittently, during this initial phase, if I turn on the AC, it'll surge to near 2k rpm for a second.

Seems strange. I know cars will idle a bit fast on cold start, but 2 min?? Usually only for 15-20 Secs on most cars.

 

[BrooklynBay]

It usually does this in cold weather.

 

[corkey]

until the engine reaches a certain temp it will do that,,

other reason for it would be oxygen sensor heatup times,, going from open to closed loop,, that takes time,,,

 

[BrooklynBay]

Sometimes it could be caused by a vacuum leak from a hose or intake gaskets.

 

[MotorCityFats13]

if it did this all the time I would suspect a bad IAC valve, that is if they still have those on the TB after the 3rd gen.... from my understanding you have 2 sets of O2 sensors ones that heat them selfs up and ones that need to get warm the ones that heat up take over open loop until the other set get warmed up by the exhaust so there would be no need to run the EGT's up with higher RPM's

 

[Jimmy69]

I wonder why everyone is forgetting how important the ECTS is. This is worth a try. First check this sensor for resistance because this particular sensor affects your egr evap startup and a lot of different things that has to do with the engine. It will cause you rough idle, hesitation, stalling, rich condition. All you need is ohm meter or multimeter.

 

[Jimmy69]

If you have a faulty ect sensor that stuck in hot it will send signal to your pcm to reduce the fuel mixture because the signal sent from a faulty sensor is that the engine is in its operating temperature while infact youre only about to start you car and this will cause you a lean condition, hesitation and even stall. While a faulty sensor that is stuck cold will cause rich condition, High rpm at idle rough idle, black smoke and will affect the egr valve not to open because the the signal sent to pcm is that the engine is still warming up. Hope this will help.

 

[BrooklynBay]