EZ-EFI stalling on decel

[rich22]

Guys,
I have an issue that has been plaguing me for months. SBC, 425hp, nothing too radical.
Fuel pressure set to 43, accel is great, starts right up everytime, awesome on top end, etc. Idle bounces between 750-800rpm, right where I want it when warm. I have a manual transmission, and when I clutch it from a cruise, the engine wants to stall. If I'm lucky, it will dip down to 400-500rpm, 'catch' itself and recover to 800rpm. Most of the time I actually have to bump the throttle to keep it from stalling out completely. I have actually gotten into the habit of doing this at every redlight - clutch it, knock it out of gear, switch clutch foot to brake pedal, then bump the throttle. Sometimes Ill just pop the clutch a little right before I stop to bump the motor back up (or restart it before I lose momentum). Very annoying.
I am using a hydraulic booster for my brakes, so the obvious leaking-vacuum-booster scenario is out. It doesn't seem to matter if the engines warm or cold, if its 30 degrees outside or 99, it has the same behavior. TPS reads 0 with my foot off the throttle, and doesn't jump around at all. Any suggestions?

Thanks,
Richard

[SoCal]

As you probably know, the air the engine uses at idle comes from two sources - around the throttle blades and past the IAC motor. It might help to alter that balance so that the IAC's contribution is smaller. That way when the throttles are closed, no matter what the IAC is doing, the engine will have more air to work with.

With the engine at full operating temperature, look at "IAC" on the handheld's live display. Its best to do this after some driving. It's range is 5-180. It is normally somewhere in the 20-30 range at idle. If that is the case here, use the idle screw to open the blades a little bit. The "IAC" reading should decrease. More air around the blades means the IAC motor won't need to be open as far. You can try adjusting the blades until "IAC" drops all the way to 5-6 to see if it helps. After the throttle blade adjustment, turn off the engine and go into the Advanced Options menu in the handheld and use the Calibrate TPS function. This is necessary because the resting position of the blades has changed.

[rich22]

I will give it a shot this afternoon.

Thanks,
Richard

[Curby]

I would like to know if this fixed the problem.

[rich22]

I tried adding more throttle blade opening and recalibrating the TPS.
I now have it where at idle, the IAC reads 5-10 counts, and the engine is running at 900rpm.
The stalling issue seems to have subsided, but the side effect is weird.
When I let out of the throttle and clutch it at 3000rpm, the motor falls to 2500 and floats there for a few seconds before falling down to idle. Thoughts?

[SoCal]

Great. Glad to hear it is better now. Thanks for reporting back.

The hanging on to revs thing may be related to a function known as "throttle follower". It forces the IAC motor open as you apply throttle. It is meant to prevent stalls when you jump off the throttle. The idea is that if the IAC is already partially open, it should help keep the revs up. Then RPM can be eased down to idle speed as the IAC closes. When a throttle follower is set aggressively (IAC commanded open farther), it can have an effect like you are describing. You can rev it up fine but it takes a while for RPM to drop afterwards. Like a lot of things, it is a balancing act. You want plenty of stall protection without hanging the revs for too long.

Adjusting your throttle blades to get a lower IAC position may have simulated making the throttle follower more aggressive. As an example, lets say your idle IAC reading was 40 before. And now it is 10. And lets say the throttle follower kicked IAC open to 100. Before when you got off the gas, the IAC would have to move from 100 down to something close to 40 before it was in position to start controlling engine speed. Now it has farther to move - from 100 down to 10. These numbers may be off, but hopefully they help show where the delay could be coming from.

If you have some room between your current throttle resting position and your original setting, you can try easing the blades closed a bit to look for a happy medium in there that works on both fronts. Again, remember to redo the TPS calibration after any throttle adjustment.

[harry_427]

Did you fix the rpm "hanging on" problem, because my vortec ecu v8 s10 does this as well?