idle/stall issue.. help?
 

Ok. 05 Monte SS. Mods are as follows:
cai
zzp high flow tstat
zzp coil packs,
zzp plug wires,
tr6 plugs
zzp catted 2.5 dp
zzp pcm


before we installed the pcm it was throwing rear o2 codes. I told them at zzp that I had them and they said it was no problem because those codes were already removed in the tune. I installed the pcm and still had rear o2 codes. I just put a new rear o2 in it, and the cel came back on in 15 minutes of driving. Its now completely randomly having idle problems. On startup, sometimes it will idle anywhere from 1300-2000 rpm until you give it a rev and it will immediately settle down. Other times, it will the the extreme opposite. It will bounce from 300-500 rpm sounding like it has a giant cam. Sometimes it will stall sometimes it'll keep doing it. If you shut it off and start it back up, 9 times out of 10 it will run fine. Now when it comes to the after driving for a while problems, it NEVER idles high. Sometimes if theres light wheel spin, as soon as the traction control hits, it will just die immediately. Other times it will just shut off as soon as you hit the gas. Then other times it will start doing the loaping until it stalls. Now it has front and rear o2 codes. The only recommended thing I haven't done yet is get a case learn. I'm hopefully getting it done in the next couple days. Do I need an upstream o2? All vaccuum lines look good other than right on top from the Tb to what I think is the boost valve. They're pretty dry rotted, but I don't feel them sucking air anywhere. Could this be related? It sounds like a maf iat or iac problem to me, but its only throwing o2 codes. I'm not sure where to go from here other than wasting money on sensor after sensor.

I know when I had my pcm done I had to have a crank relearn done at the same time, this could be part of your problem. Your downpipe would cause the 02 code, you can also buy a bung extender from zzp that should eliminate the problem but in my case the pcm tune eliminated the code from coming up. I would also pick up a can of maf cleaner and give it a good cleaning, they are particularly prone to failure on these cars and it doesn't hurt to do it periodically. The other thing is you may have gotten a bad plug wire or coil or there is a bad ground on the coil causing the stalling issue, I know it is not likely but it does happen from time to time. Also check your throttle position sensor they are another known issue that can go wrong from time to time.

Maybe pick up an 02 from a wrecker and check it before buying a new one, I know it's an added expense but I personally don't know of any way of testing them other than the computer telling you it is bad. The zzm tune should have taken the rear 02 out of the equation so there is a possibility the front 02 is gone bad.


Symptoms of a Bad Oxygen Sensor
When you have a bad oxygen sensor, your vehicle will run less efficiently, it can sometimes have a poor idle, erratic jerking at steady throttle, hard starting problems, cause the check engine light to come on, and will cause high fuel consumption.

There is a chance your egr could be gone as well giving you some of the issues you are experiencing, although when mine went it threw a code showing bad egr, but worth checking to ensure it is sealing properly, it is only two screws holding it in

This article tells you how to check the 02 sensor with a multimeter

Part 1 -How to Test the Front Oxygen Sensor With a Multimeter (2.2L GM)

I thought vacuum problem even before I read your mentioning of it. You can take a can of carb cleaner and mist the area around lines and if the idle changes there is a leak in that area.

A bad 02 sensor can cause your pcm to cut fuel as it thinks it is running rich. Since you say the o2 sensors have been replaced, how do you feel about the connectors? Okay condition, crusty oil soaked? Are you getting as low voltage code? I mean for some reason they were bad already before the pcm upgrade. Perhaps clean the connectors with a good electrical component cleaner.

Perhaps ZZP needs to have your PCM returned at their expense to remove the ability to read that code. I mean you did mention it to them, they said they had it covered and you are using a fair amount of their components. Wonder if they need to go through the whole tune to see if one or more of the tables are corrupt and causing your new problems, I mean one thing is bad with what they said already. Never hurts to inquire with them, they have always treated me right.

They wanted me to send it back if the problem didn't go away after I got the case learn done... but not at their expense of course...