I am wondering what it causing my 3.4 v6 to NOT rev High on cold start up. When I turn the key it starts but shuts down unless I step on the gas a little and hold the idle. Normally it fast idled for warm up and "kicked down" on its own to a warm idle of 800RPM. Now it just idles at 3-400 RPM right from the start. (after I hold the gas and let it get warm up a bit). What components are responsible for the fast ide warm up and what would cause their failure? Sensors? I really know nothing about EFI. I am a 4 bbl and headers kind of guy. I can do the work myself along with help from the Haynes book, but I can't identify this problem. This truck usually makes this intermittent short humming noise when sitting. Now it does not. Is this part of the problem? It comes from the box in between the Master cylinder and the circuit box under the hood drivers side. Don't know what it is or why it does that but it always did but now it doesn't. Any takers? Thanks so much

 

That humming noise has nothing to do with this. That humming noise is simply the fuel EVAP system relieving pressure. Mine does it too. I assume you have a 96 or maybe a 97?

Did this problem you're describing gradually develop, or was it a sudden thing?

 

im new to this 3.4 thing so bare with me. the older efi engines had a the efi time delay switch that would idle up until the engine reached temp. its worked together with the tps and coolant temp sensor. I also have that intermitted buzz/hum in the same location i thought the previous owner place a bomb in there some where i wonder what it could be.

 

It was sudden

 

It is a 96 xtra cab 3.4 A/T 4x4

 

I grew up in Sayville LI by the way!

 

A while back I had an O2 sensor go bad and found out by going to Auto Zone and the guy plugged into theport under the dash. If they do that agin even thought the check engine light is not on will it discover the problem via a code?

 

Probably not unless a code is stored. It never hurts to have them plug the OBD reader in again just to see though.

This could be a number of things, however I do not have the FSM in front of me so it's hard to say exactly what I would test first and how I would determine if a part is faulty. I am willing to bet the testing procedure will lead you to where the coolant passes through/under the TB and possibly the IACV or a similar part, but that's just a guess at this point.

 

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