PSUSkier

So I noticed an interesting behavior now that I've been running around with this H.O. kit for about a month. If I'm cruising for a decent strip (lets say a mile or so) and leave off the gas to coast, my A/F ratio shoots lean by anywhere from 16.5 to pegging the gauge at 18. If I put it in neutral or push in the clutch the idle will sometimes stutter a bit between 500 and 750 for about 3-4 seconds at which point the engine will suddenly jump back to normal AFRs. Is that normal behavior for this kit or is this a tune issue? Cruising, normal idle and WOT are spot on where they should be.

jahudso2

When the throttle is closed, there is no fueling. That is how you get engine braking. You should definitely see high A/F ratios with no throttle input, because your A/F ratio is 1/0 or infinity.

Simon1

Your AF will vary greatly in normal driving. It will dip into real rich or real lean on start up and slow down. Don't worry about that.

With my trubo the AF bounced around alot even at idle. It only settled down under WOT.

With the KB it is more steady.

If you are not throwing codes, your fuel trims should be within the recommended specs, if it was running too lean or rich, then the car would throw codes.

The RPM control when getting off throttle is most likely something that can be adjusted with tuning. Sometimes a cam or a vacuum problem, or letting unmetered air in or out will cause the fluxuation.

Is it different with the AC on or off?

Simon1

Generally with the throttle closed, foot of the gas, your AF will be high 17s or better. Not a concern. Some tuners hang the RPMs a little bit depending on what the customers wants.