2008 LT 97k miles just had transmission replaced and when I picked it up noiticed a hissing vacuum leak like noise from the drivers side dash area, could swear it was coming from extreme left ac vent, which stops when I lift my foot from accelerator. I have checked everything, found a tear in the air intake hose, and made a temp repair, but still persists. Don't think it is wheel bearing since it stops as soon as i let up on the accelerator, while wheels are still turning.

Anyone have any ideas? Thanks in advance for any advice.

 

Check the flex pipe. Don't argue, just do it.

While you are under the hood check the vacuum hose that goes to the MC booster.

 

thanks i will!

 

Flexpipe X2, also this hose

 

SO...flex pipe no leaks, vac hoses no leaks...anything else i can check for? 2008 LT 97K miles noticed when i picked it up from transmission shop after having trans rebuilt. ALSO...trying to solve rough idle problem, does not get noticably better with ac compressor off. installed new MAF on Wed and by friday had check engine light code P0171. does anyone know what we may have done wrong?

 

Re the P0171 - Are you sure the new MAF is properly installed? You can put the original MAF back in and see if that alleviates the code.

Why did you not take it back to the Transmission shop when you found problems?

 

As per

https://www.obd-codes.com/p0171

It’s because of a faulty MAF sensor, now you have a new one double check the wiring to it, all tight and no bent pins!

 

Turns out hissing noise was engine noise coming thru fire wall where steering column goes thru, rubber boot had come loose. So excited to have my quiet car back!!

 

Glad you found it, thanks for updating!

 

Awesome, a no cost fix! That boot is tough to get installed correctly