Mystery Stumble

[Rick Simons]

This weekend I re-installed the JLT CAI, making sure that there was a good seal between the intake tube and the MAF- a leak here is what caused an intermittent full-lean condition that I mentioned in a post last year. I also loaded the appropriate tune for the CAI. With the CAI the engine has a stumble/hesitation when I blip the throttle quickly enough from idle. If I blip it fast/far enough, I'll get the hesitation AND a backfire. Note that this is only from idle; from 1k rpm and up it responds perfectly. I've checked every possible vacuum leak source I could think of, and nothing. No CEL either. If I put the stock air filter setup up back on and load the tune for it the throttle response is perfect everywhere. I've reached out to Lito to see if he has any ideas.
Open to any suggestions; thanks!

 

[Juice]

You are describing a "lean pop". And since you changed the airbox out for the cai, the tune is too lean, atleast off idle.
Time to check fuel trims STFT & LTFT and see how much the pcm is adding fuel. With the pop on blip, IMO it is just a matter of time before a system lean code pops up.

 

[Rick Simons]

You are describing a "lean pop". And since you changed the airbox out for the cai, the tune is too lean, atleast off idle.
Time to check fuel trims STFT & LTFT and see how much the pcm is adding fuel. With the pop on blip, IMO it is just a matter of time before a system lean code pops up.

Good info. I do have a separate tune for the CAI, which hasn't been altered since the last time I had the CAI on. I've put the stock setup back on for now and loaded the tune for it, and all seems to be well, except for a rev-hang issue which Lito is looking into.