Ok here'* the deal..I have a 1995 Bonny SSE and am unable to find the cause for the lean signal from my O2 sensor. I have gone through ALLData several times, forums, everywhere. No Luck. Vaccum is fine, fuel pressure 41 psi, idle 750(minor stumble), check injectors, new fuel filter, plugs, wires, maf sensor, IAC, air filter, FPR, battery. Have checked all grounds and cleaned. Any suggestions would be really helpful.

I had the same problem with my 94 SE but the code for mine was a low voltage O2. It ended up being a bad brake booster. It was somehow letting air in (Vaccum Leak). Try checking your EGR possibly I know that can mess with your idle.

Thanks for the response..so there'* alot i didn't mention that ive done..didn't want to overwhelm everyone. I have checked the EGR and cleaned it. Originally I had a code set for it. EGR FLOW and PINTLE codes. Those have since disappeared. I checked the brake booster..plugged the vaccum to see a change on o2 mv readings. stays steady around 0-4 mv but seems to oscilate lean/rich with a bit of throttle or while driving. Everytime I think ive figured it out nothing seems to change the low voltage reading at idle. Maybe a bad coil? It seems to run fine on the road. Just stumbles at idle.

how many miles on the car, when was the last time the oxygen sensor was replaced, and if it was replaced by you, what brand was it.

168,000 mi, oxygen sensor new, few days ago, bosch...heard they can be bad for bonnys, new intake plenum as well about a year ago. got coolent into my cylinders and hydrolocked...terrible mess. ended up putting new head gaskets in then found out the plenum issue. not sure if my cat was effected by the coolent. The thing that gets me is that the sensor will read between 150 mv to 900mv+ on acceleration or throttle over 2000 rpm.

alright. they're not bad for bonnevilles, they're bad period. they suck. you need a delco or denso, otherwise we can't rule out that its not the sensor in the first place.

also, are you getting this code from the upstream or downstream sensor (i can't remember if you have a downstream sensor or not)

cats and o2 sensors are two things that dont like coolant. if you ingested coolant...your cat probably needs replacing. that and the bosch...

Im going to get delco o2(only one) and see if that helps...then comes the Cat. Need to check on prices usually not cheap. Thanks for your assistance. Ive spent about 20+ hours diagnosing this problem and am running out of steam. Tracing wires and checking connections can make you go blind.

I belive the 95 does not have a downstream O2, but I could be wrong. If the cat is bad ZZP has them for about $70 or $80, then you just need it installed. But the cat wont make you run lean. So lets fix one problem at a time. Here'* alink for O2 sensors. http://www.rockauto.com/catalog/raframecatalog.php?

So I have some new info I was unaware of I was just checking my scanner while driving...safely of course, and I was looking at my KS Counter and it was climbing throughout my drive home. I know that the engine is not in prime shape ie plenum failure, but i was wondering if my KS would affect my O2 Mv? I ended up pulling that bosch sensor and put my old one back in. A local shop has delco and am getting a price and stock verification any minute. Also the two gauges in my dash Volts and oil pressure haven't been quite right since plenum failure. They seem to work half the time jumping all over the place the other half. I was thinking maybe a instrument panel voltage regulator, but am not sure. Along with that track of tempermental guages is my scanner. It seems to disconnect for no apparent reason while im checking my readouts. It doesn't happen alot but I'm thinking it shouldn't be happening at all. Oh, and not to write a grip load here, but while im on that topic i noticed that my a/c when turned on will engage and disengage every three seconds or so. Not sure if these things are related, but thought I'd give you as much info as I can.

KS won't affect O2 readings. They're both symptoms of the same problem.

Running lean will cause knock. (KS).