So, I made a mistake when I tried fixing another small issue under the hood. Long story short, I have a Paxton S/C and while I was re-assembling the intake tubing leading up to the TB...apparently a small vacuum line popped off that runs from the bypass valve (which is connected to the intake piping leading up to the TB) to a small 3 way nipple that has other vac lines connected to it. I didn't know this at the time, and I drove the car less than 1/2 mile and noticed something was jacked up. Engine didnt want to rev above 2K RPM, etc.

Fast forward, I reconnected that vacuum line and the car now runs, but it runs very rich at idle and bogs down to about 500/550 RPM when slowly approaching a complete stop. Once completely stopped, the RPM will recover. I have also noticed, some black soot coming out of tail pipe on the first initial cold start.

What I have done so far, took it to a local speed shop and they believe the tune got screwed up and there is nothing they can do about it without completely starting from scratch. ($1,100.00)
Talked to original tuner, and they too cannot really do anything other than either doing a tune in-person (4hr drive), or a custom e-mail tune ($650.00) from Brenspeed.

Pulled TB off and cleaned it (pretty much clean), pulled MAF sensor out and cleaned it, cleaned air filter. Next, relearn procedure.
Performed the idle relearn procedure and believe that helped, but still bogs 1/2 the time.
No check engine lights, even plugged in obd2 scanner to see if anything was stored, nothing.....no pending, etc.
My Cobalt A/F gauge will read 16 when slowly approaching, then go back to normal 13ish.

I am not familiar with readings for data logging, such as what voltage the O2 sensors should be at, etc.

Any help would be appreciated.

 

 

Just now got a Pending DTC of P0153 O2 Sensor Circuit Slow Response Bank 2 Sensor 1.

 

Ok, so I did a little research and while the vacuum tee/hose situation is the 'seems like you need to check that over again' issue to me, the now pending P0153 indicates that yes, most likely you have a vacuum leak causing an air intake issue which is then causing the rich condition. The other two issues are an exhaust leak upstream of the O2 sensor(s), and then the O2 sensor itself, or the wiring thereto.

It's not likely the tune, I'm guessing, since it was fine before the tee went silly. I'd suggest getting a smoke machine run on the car to find any intake issues, or even exhaust (just plug up one tail pipe, smoke machine the other, see where smoke comes out). Could even be some sort of evap issue, maybe a line has cracked... who knows. I'd also recommend an actual scan tool that'll get all kinds of data run on it, pay for the diagnostic. You can pull lots of hair outta your skull and spend quite a few bucks shotgunning parts at this problem, where an otherwise relatively small amount of time and money to know the problem is 'this thing right here' would be worth it.

I hope that helps, even if it's not exact. Good luck!

 

Thank you for that information. I will try and re-check that fitting again....its such a PITA to get to it. You are right, I need a mechanic with a smoke machine to check the car out. Thank You!

 

How did the tune get screwed up? Did someone change the tune while this vacuum issue was happening?

Tunes do not change by themselves; so if nobody changed the tune, then I would not worry about that. Once you get the physical problems all sorted, a reset by disconnecting the battery might help make the computer relearn anything it might have learned that was wrong.

 

As mentioned above, that vac line was the only thing that happened, then corrected. So, I am currently unsure what is happening now. All I can think of is that something got fouled up and is messing with the computer, or a leak. The car is currently in the shop getting the smoke test done.

On another note, for those who replied to my belt tensioner deal/chirping. Had a new belt put on and the tensioner changed. New tensioner hardly moves at all compared to the old one. No chirping....some pullies had some gunk on them, but was told they all spun smoothly.