Engine wants to stall after deceleration...


New Member
Sep 30, 2001
Hi guys,

So I'm making progress with the FAST tuning. But as usual, I have a question.

When I'm driving along and come up to a stop, I'll generally engine brake the car by leaving it in gear, then press in the clutch right before stopping. Well, for some reason when I do this, the engine wants to stall. It will stumble and idle around 600-700rpm until I blip the throttle, and then it will recover and idle fine.

Any idea what might cause this? Or what setting in the FAST ECU I need to change to fix this? Nothing is jumping out at me from my data logs. The only thing I can think of is the IAC is closing down while decelerating, and maybe that's causing the problem. But using the throttle follower table, there isn't anything I can do.

Any thoughts would be appreciated!

I've found that it's very tough to tune the VE numbers for decelerating. The problem is that the exhaust takes a long time to reach the sensor- you have very little airflow, and a relatively dynamic engine situation.

If your A/F numbers are about those that you'd be idling at, then the next thing I would do is just fool around with the VE numbers (keeping in mind the very slow reaction of the O2 sensor). The best way to tune those VE numbers is going fast on the highway, let off the throttle in top gear and give the O2 several seconds to figure out what is happening. Hopefully in the time you slow from 65 to 50, you'll have a decent enough idea how to adjust those VE numbers. If that doesn't work, then do some trial and error.

If you get good results while decelerating, I have a feeling it will return to idle better.

Just my guess, hope this helps-

-Bob Cunningham