I've been trying to find this for some time. Disconnected all sort of things (IAC, MAF, Set timing, etc.) and it still surges.

Tonight, tried to run with out the O2 just to see. Without the O2 connected it hunts from 500 to 1000. With the 02 plugged in, it hunts from 650-800. So it is worse without the O2 input.

This is backwards as to what I expected. I figured the idle would have been better without it, but I am not sure what it does.

So it is a lazy O2 sensor? Or is the O2 doing what it should, but the problem is really fuel delivery and the O2 is just trying to compensate for some poor flowing injectors?

Anyone with a bad O2 and symptoms?

Mark.

 

Have you checked for vacuum leak?

 

Yup - I have looked for a vaccum leak.

I have no EGR. Re-torque intake bolts, actually replaced them all. Installed new upper and lower TPI gaskets. The only vacuum thing I have hooked up is the AFPR. Everything else is blocked.

I suppose it could be a leak, but I am surprized by the symptoms. I've isolated most things that can cause the idle to change, all except fuel. So even if I had a vacuum leak, it still would not surge in all the cases I tested.

rather frustrating.
Mark.

 

If it idles badly when cold and warm, the o2 sensor is not the problem, although changing it will not hurt anything. Vacuum leaks are easy to find, so if you haven't found any by checking with water or something combustable there aren't any. Have you cleaned your throttle body and IAC out?

 

When it is cold and the idle is 1000+ it idles fine. Even with the scanner hooked up and the engine warm, in the diag mode it idles at 1000 and it is smooth. It only does the idle hunt thing once it warms up enough that the idle drops to the 650 range ... I assume this is closed loop.

Mark.