Thread: New Front O2 leads to issues...

Hi all, Im hoping someone can help here. I have limited time at home and need this car to be reliable when I am gone. Car is an '03 GT with 138k.

We recently did the following repairs: Rebuilt transmission 07/15/09, new catalytic converter (due to clog) 07/15/09, new front O2 sensor, air filter and oil change 09/12/09.

Two days after installing the new O2 sensor, we were still enjoying the newfound performance when the SES light came on. I had it scanned and it showed PO171 but was still driving fine. I wondered if swapping the front O2 sensor and leaving the old rear one in was causing it to run lean, but that didnt really make sense. I checked that the new O2 was in tight, also inspected the vacuum lines and the pcv/egr/manifolds for leaks. The only thing I noticed was the rubber seal on the sensor plugged into the top of pcv housing (map sensor?) was slightly torn.

This morning, on first start, the idle is fluctuating between 700-1000rpm every few seconds and it will occasionally surge higher and/or die. It does this in and out of gear. It doesnt hesitate under throttle, however. It has normally idled at 900rpm for the 2+yrs we've had the car. I am going to scan it now to see if a code other than PO171 has been stored.

Any ideas or similar experiences that will shed some light on this today would be much appreciated. I am an otr driver and am leaving out soon. Thanks much!

Update:

Code PO171 is gone and PO131 showed up. So we went from reading lean to having low voltage readings on the new sensor. I am going to replace the O2 sensor I installed (Borg Warner) with an AC Delco unit and monitor it. hopefully it was just a case of you get what you pay for... Also slathed some black rtv on the map sensor gasket since that slight tear may create a vacuum issue later on.

Anyone ever experienced a faulty O2 sensor causing idle fluctuations and surging/dying? I suppose if the readings were far enough out of spec in closed loop, then yeah it might throw the ecm for a loop like that. Im hoping this corrects it...

ok so the Delco O2 sensor has been in for awhile now. Apparently it is much less sensitive than the Borg Warner unit. No codes thrown yet but the car seems much less responsive. Fuel mileage is still horrible, though, and there is a slight smell of coolant. So im looking at doing an intake manifold job to try and resolve any possible vac leaks. Are there any other known vac leaks i should be chasing?