Reciently whenever I start my truck, both cold or warm, after about 2 minutes the RPM will drop and start sputtering and a loud sucking or whistling from the IAC, this lasts for about 20 seconds and then it will return to normal, I just replaced my front O2 sensor suspecting this was the problem but it is still the same, although not quite as severe, but seems to be going back to the same severity as each day passes.I checked my fuel pressure and it is steady at 48/49 psi, any ideas?

 

Did you disconnect the battery for a while after replacing the sensor?

 

yes I did disconnect the battery

 

Plenum is fixed, o2 replaced. What if anything was done about the cat?

 

The cat is gutted, but now that you mention it......I had a muffler shop gut the cat last fall on the road when I was pulling my trailer and thought it was plugged (due to low power and a #8 missfire....which i believe since then turned out to be crap in the injector screens) anyway they cut the side of the cat out, gutted it and welded a cover back on, the weld job that they did isn't quite "air tight" and I get a little bit of exhaust leaking out of the weld....could it be getting air sucking in and messing up the O2 reading until it heats up the cat?....just a thought

 

I'm surprised a shop would do that. I'd check it to see for my self.

 

You mean gut the cat? or do a bad weld job? I watched them so they definatly gutted it, there is no emission testing anywhere near the town I had it done in.

 

I'm surprised because it's a federal law to have a working cat on a vehicle that came with one. Most shops wouldn't touch that with a ten foot pole.

 

small town Canada doesn't seem to know about such a law, or maybe just different laws up here ? the only emmision testing that I know of is in larger Canadian citys....either way, it's gutted.....let me reverse this conversation a bit and just say that I did it

 

Just checked with a shop today about doing that and he said it was a $10,000 fine for him and a $2000 fine for me. That's down in the US though.