Fluctuating idle 99 Passport

I've had a fluctuating idle for a while now, but its gotten to the point of stalling sometimes. It will go from about 500 rpm's to 1500 rpm's back and forth. I have recently changed spark plugs (ngk) and cleaned my egr. Seemed to get worse after the egr cleaning, but at least the pinging is gone. I just got a CEL P0171 O2 sensor, but this is the first time I've had the CEL go on, and the problem as been around for about 6 months to a year. Little wary of buying an oxygen sensor if it might be something else. Any advice would be much appreciated.

I had the exact same problem a few months ago. I did all you did, and it seemed worse. I had the same code and the idle fluctuation over many months. I got the code after moths of the idle fluctuation. It turned out to be the intake manifold gasket. I bet the house on the intake manifold gasket being your problem as well.

sounds like a classic case of intake gasket failure. your dealer should replace this for you (I think) free of charge. search "intake manifold" in the forum for more threads on this issue, and check out the FAQ's at the start of the forum.

Is this the case with a1997 Rodeo as well? With the 3.2 L V6

sounds like a classic case of intake gasket failure. your dealer should replace this for you (I think) free of charge. search "intake manifold" in the forum for more threads on this issue, and check out the FAQ's at the start of the forum.