Hello all and thanks in advance.

Moderator,, (i post this also under transmissions, not sure which forum would be best)

I have a suburban 5.7 TBI and 4l80.I thought the knowledge on this forum might be the best place to post.

My issue is when decelerating, my motor surges +/- a few hundred rpm. It's like someone it pulsing the brakes. I use WINALDL and have a MSD trans controller and nothing looks abnormal.
My first thought was the convertor locking and unlocking or the IAC controller going crazy but nothing shows up when data logging.

Has anyone experienced anything like this. My motor is basic, 9.5/1, small lunati cam, header, etc. I am running a OEM small block 4l80 convertor.
I do not believe vacuum is the issue, I have ~18 at idle and this problem was not there a few months ago.

The set up runs smooth as silk the rest of the time.

All help is greatly appreciated.
Chris

 

Update,

It was a leaky injector. Apparently the TBI cuts the fuel at some point on decel and with the small drip it would boost my RPM.

 

Interesting. I would not have thought of that.