Less than a year ago and less than 1000 miles, I put a new AC O2 sensor in the vette. The car seemed to run much better. All this time, I have continued to work on a rough idle problem. Today, I ran a scan on the car and found the O2 to stay (locked) at .18 volts and the air fuel ratio to be about 22 to 1. Has anyone had problems with a new AC O2 sensor? Any idea on what caused the sensor to go bad? Headed to the parts store tomorrow!

 

Dead O2 and a warm motor should throw a Code and have it running on backup. I know you've been chasing the rough idle for some time. Coolant will kill the O2 and you have an '89. If you haven't checked #7 yet for a leaking head gasket, you might want to do so now.

 

SunCR: I am a relatively new vette owner and am not aware of the #7 cylinder problem. Would you mind providing more information on this issue? How should I check for a coolant leak? I do have a coolant pressure checker and to the best of my knowledge I am not losing coolant! I just finished learning about Multec injector disease on my 89 and now this??? Thanks in advance for your assistance on this! :confused:

 

A victim of #7 here. What happens is that when aluminum heads were installed on our cars (87 and later) the coolant would cause galvanic corrosion of the head gasket to occur between the iron block and the aluminum heads. It's quite common. Not changing the coolant on a regular schedule aggravates the issue.
Look for white steam clouds coming out of the tailpipes, vanilla milkshake lookin' oil, a gurgle sound in the radiator. Mine literally hydrolocked when it happened. Motor would not turn over as water does not compress.

 

As best as I can tell, mine started leaking at about 25,000 miles. Symptoms were cruddy coolant within 6 months or less and very few miles; aux fan coming on in cool weather though temps would cool down to about 220; plugged heater core; #7 plug was always a little cleaner than all the rest; compression 170 all around; radiator pressure normal, and because the coolant got dirty so fast, I never had it in there long enough to notice any loss. Idle wasn't bad, but it wasn't perfect - ECM would target 575 and idle would skip around 590 to 610, so I replaced a ton of good parts. GM's Bulletin wasn't issued until '90 - dealer consistently missed it under warranty - the best I ever got was "boy the coolant is really dirty". Multiple complaints on file by other owners with NHTSA, but none of that was online in the early '90's - about 5 still posted today. Finally let loose at about 50k. Pulling the heads was a real eye opener and one of these days I'll take some pictures of the old ones and post them. Gasket materials and heads redesigned, but only the '91 L98 has them. You should pull #7 & #5 plugs and compare them. If you use oil on the plug threads, it may be washed away on #7 if the problem exists. Now that I've fixed it, idle is better than it ever was (though I replaced the injectors too); aux fan never comes on even running stock thermo.

 

Forgot to mention it did kick out a 44 or 45 once or twice, but lacking a scan tool, I'd simply replace the O2 and that would clear it up. That being the case, I didn't look into any further.

 

My engine was rebuilt 3 years ago, I'm guessing the engine builder would of used a good set of gaskets instead of the factory crap ones.... I hope :rolleyes:

 

Sam, had the car gone into "CLOSED LOOP" already when you saw the static O2 value? A static O2 value in closed loop is an immediate sign of either a failed sensor or a failed connection back to the ECM. At idle you should see the O2 swinging from 999mv to 000mv over and over and over with the crosscounts steadily going up. I had one fail in under 1000 miles on my own car. It happens sometimes. Thankfully the one i bought had a lifetime warranty.