How old is your O2 sensor, and what brand is it?

 

Not sure the age of the O2 sensor. Couldn't find a branding on it, but did see 1212ae on it. Replaced the cap and rotor today. They were a little corroded, but didn't seem to fix the issue. Hooked it up to the oscilloscope and am getting a high voltage reading on 1 and 8. Pulled the wire off of 1 and tested the ohms. Got no reading on it. Tested a new plug wire and got a solid reading. I'm thinking 1 and 8 plug wires are shot. Ordered some new wires tonight and I'll put them on tomorrow evening after work. Fingers crossed.

 

So I replaced the wires. They were definitely overdue. Still having the hesitation issue. The O2 sensor still seems to be responding as it should(or at least I think), from .08v up to 1.0v fluctuating back and forth quickly. Not sure where to go from here.

 

I would try a NTK O2 sensor. Yours may be working, but with age, they don't always read correctly. Some Seafoam or cleaner of your choice for a couple tanks of fuel wouldn't hurt.

 

So I replaced the O2 sensor. The old was a NTK and so is the new. No real noticeable difference. I do have a whistling sound coming from the engine (sounds like a turbo spooling when I accelerate). Looked around and didn't find a turbo haha. I will poke around the vacuum lines to see if I can find anything out of sorts. Would a plenum gasket failure cause a whistling sound?

 

In my case like that it was the airhat gasket or a bad PCV valve. Check them if it's hard it's no good. A good way to check for a vacuum leak is get a can of steering fluid and spray the lines, when the engine revs you found where your leak is.

 

I replaced the PCV when I did the spark plugs (I broke it when I put the CPS back in after the tranny rebuild). I sprayed carb cleaner all around the air hat and didn't notice any change in rpms. Cruise control and my air vents are all working properly, so I don't suspect vacuum issues in those common areas.

 

Interesting I don't think carb cleaner is as flammable thought. Do you have an aftermarket intake?

 

I've heard you can use water as well. Will cause it to drop rpms, but not as much risk of fire. I have a stock airbox.

 

Have you tried taking the air filter out, putting the hat back on, and running it?I Do you hear the noise while your under the hood or is it just when you're driving? If it just when you accelerate, might check your fan clutch. I would check/test your ignition coil. Long overdue plug wires can toast them.