What are the things that could cause poor gas economy? I just put new ngk plugs in about 1,000 miles ago

 

If I replaced iac but did not reset pcm when I did, so k though it wasn't the problem and returned it, would it be wise to replace iac again but reset pcm and see if it makes fuel economy go up and vacuum leak stop? And will it always throw a code? I have a code reader

 

1) Make sure your air cleaner is clean.
2) Make sure your plugs are gapped correctly.
3) Cap and rotor.
4) Clogged Cat.
5) Plenum gasket blown.
6) Fuel Injectors worn.

 

Also what should the voltage be on my o2 sensors? My code reader gives live data for the voltage on #1 & 2 bank 1

 

It will throw a code when the engine gets to normal operating temp. The check engine light will be illuminated and stay lit until you reset.

My IAC went out too, the truck would stumble at idle and idle really low - there would be a vacuum sound from under the hood and the Check Engine Light stayed lit.

 

I didn't replace cap and rotor, just plugs. Should I start with that for fuel economy? And if it is my plenum gasket, how long does it take to replace?

 

Here is a good read on O2 sensors: http://www.mr2.com/TEXT/O2_Sensor.html

 

Mine is doing the same thing, but my check engine light isn't on. Is there a possibility that thats the problem?

 

I would start small first, while replacing the plug wires, grab a flash light and look in the TB, look for standing oil in the bottom of the intake. This usually points to a bad plenum gasket or a really bad PCV valve.

If you find a blown plenum gasket, you may also have a clogged cat as the oil is sent through the engine and absorbed by the mesh in the cat.

This can cause a serious issue with power ect.

To check the cat, pull the forward (upstream) O2, start the engine and see if the engine seems more powerful. That little bit goes a long way if the cat is clogged...

 

Sounds like a bad IAC, if you already replaced it and it's still doing it - it could be the sending unit or something down the line that's telling the IAC to open when it should be closed.