2001 SS 3.8L:

started stalling at idle and sometimes surging, got trouble code rich bank 2, then it went thru some coolant and I changed the LIM and UIM gaskets. After gasket change still stalling at idle and sometimes surging, replaced IAC solenoid still happens so I am thinking this is either the CAT or O2 sensors. After changing LIM/UIM gaskets haven't seen a new code yet, hooked up scanner and am getting reading from about 25 to 860 on the first O2 sensor and around 250 to 860 on second O2 sensor, ST trim pretty steady at -12 will go to 2 though and LT trim holds at -25, fuel pressure at 40psi. Thinking its the CAT but don't know if the O2 sensors could be bad, I'm sure it swallowed a gallon of coolant until I got it home and found out about the leaking IM gaskets. Also now after IM gasket fix when I start it up in the morning it makes a ticking noise until it warms up, drives fine when cold also, no stalling or surging. Thinking that it is a bad CAT and making that noise until it warms up? Don't know for sure, Anyone have an opinion on this? Thanks ahead of time for any responses.

Kurt

 

The O2 sensors could be damaged from running that much coolant through the engine. You may also want to pull the spark plugs to make sure they are ok. A damaged plug or one that has build-up on it could be causing the ticking noise when cold and then start working better as it gets hot. I would hit those first as this doesn't yet sound like the plugged convertor. When that happened to me, the car would lose a lot of power and 'chug' above 2000 rpm. It also would run hot during the summer from lack of flow.

 

Ok, thanks I will check into those first

 

Kef, My car had a similar problem at idle. Stalled was sporatic, and it would chug along sometimes at any speed. My issue ended up being my MAF sensor, over oiled my K&N air filter, and it took me 2 new MAF sensors to determine what it was (now I'm back to stock). So if you have an aftermarket air filter, be cautious b/c a faulty MAF sensor will do what it seems your car is doing. I just forget the exact code I was getting though but it did seem to want to run rich if I can remember correctly.

 

The fuel trims are awfull if they are that negative, the rear o2 sensor should hold steady at about 450mV-650mV when the engine is fully warmed and cat is lit off. MAF is definate possibility if you have a scanner, not just a code reader, watch the MAF reading and tap it with a plastic handle from a screwdriver lightly and see what happens. At idle I think around 8-14 g/second is about normal quoting specs, I hate doing that in case I'm wrong. The #'s for the o2 sensor are good for the front sensor but anything below 100mV is kinda low. Check for fast steady switching no flat lines for B1S1 when it's at operating temp.

 

Well I checked the MAF sensor with the scanner and it reads around 14 and doesn't move when tapped on, getting codes P0300 and p0172. Still getting those bad fuel trims and the O2 sensors are jumping around, Sensor 1 still from less than 100 to 920ish switching steady, second sensor doesn't hold steady ranges are all over the place from 200ish to 920ish holds steadier than #1. Any more advice would be appreciated, would bad injectors in bank 1 cause the O2 sensors to be giving these readings or would bad O2 sensors cause the misfiring?