Brett Jenkins

I recently replaced my original O2 sensor with an aftermarket sensor, which subsequently blows the fuel pump fuse. So, I swapped the original back in and am now having an odd idle problem. After the car warms up, the idle will fluctuate greatly, it will dip down to 200 and up to 1200 constantly, hunting wildly. As I drive, it runs fine, but when I come to a stop, the idle problem persists. If I unhook the O2 sensor at the fuse block, the car will run and idle fine. I have unhooked the sensor and battery and let sit for a while and then hooked them back up. Problem remains. I have unhooked the batter for a while and then hooked it back up with the sensor connected. Same result. I ran a decent amount of WD40 through the system to clean out the ICV.

Any ideas or suggestions? The original sensor wasn't bad, I was just doing preventive maintenance while I was in there. I guess I fixed it until it was broke. :-)

John Speake

Even if your old sensor seemed OK once, it seems not to be anymore. When engine is warming up, car is in open loop. When water temp rises to about 60degC (varies MY-MY) then the LH ECU switches over to closed loop.

The symptoms you observe appear to suggest the O2 sensor is toast.....

Jack Riffle

I would venture to say that when you installed the replacement 02 sensor, that you scaped some insulation from it letting it short to ground. This will blow the fuel pump fuse since they are on the same circuit. And as John said, even if the original sensor wasn't bad, it appears to be now. I think you need ANOTHER new 02 sensor. Just my .02 so to speak....