EvelBist

iTrader: (1)

Idle is good @650 at start, but as soon as the throttle is tapped, idle hangs at 1500. Cable is not stuck and goes back to the throttle stop.

TPS is at .59, and I've done the IAC reset procedure.

Help please!

ULTM8Z

What year car? Everything stock?

Edit... nevermind... I see your profile. It doesn't show up on the mobile phone version of the board... only the desktop version.

Maybe the IAC passages needs to be cleaned. Have you recalibrate the ECM for your mods? Did this Just start recently but was ok earlier on?

EvelBist

iTrader: (1)

Well, no. This is a '90 corvette TPI, transplanted into a '56 GMC truck.

It's an AUJP bin, no VATS, turned off EGR by setting "EGR %TPS Disable threshold" to 99, and "EGR %TPS Enable threshold" to 99, "EGR Diagnostic Minimum Vehicle Speed" to 255 and unchecked the "EGR Diagnostic" flag. Everything else is the BIN is stock.

There is no EGR and the manifold passage is blocked off with a plate.

Is there something I'm not doing or doing wrong to causing the high idle jump?

ULTM8Z

YHas it been doing this from day 1? Do you have access to a scanner or are able to run tuner pro?

EvelBist

iTrader: (1)

today is day 1. Just started it today for the first time.

Is there a setting I'm overlooking? The truck is still on jackstands, and the trans is always in Park, could that have something to do with it?

ULTM8Z

I don't think so.

Is the engine fully warmed up when this is occuring? Does it occur only at cold but gets better with temperature? Or vise versa?

Frankly I hate the IAC. What I did on mine was to open the throttle blades until I have 0 IAC steps at idle in neutral when fully warmed up. Which means the IAC is not supplying any of the air. But you'd need to be able to see the data stream to watch the IAC steps in order to do that.

I had similar issues as yours and other issues with the IAC on my Miniram. I also zeroed out the spark correction vs idle speed tables. Doing those things resulted in a much more stable idle and allows the rpms to come back down without hanging up.

You can also play around with the throttle follower settings as well, but I'd try to do these other basic things first to see if that solves it.

EvelBist

iTrader: (1)

Engine is fully warmed. I have TunerproRT. The IAC is old, but I did clean it and the TB itself. Your issues were similar, like the hanging idle?

ULTM8Z

yeah, that, and when coming to a stop, the engine wouldn't want to get down to idle speed until a second or two after coming to a stop.

If you do a search on throttle follower steps, you can see what people have done in that regard as well.

QwkTrip

iTrader: (22)

Engine is getting too much air with throttle blade at idle position. Probably a combination of your throttle blade position and the IAC hold position off idle.

EvelBist

iTrader: (1)

Ok, too much air makes sense, but its only after blipping the throttle. On startup, the idle is good, around 650. So maybe there's a problem with the IAC? All the IAC settings are stock AUJP 8E, I havent messed with them.

QwkTrip

iTrader: (22)

I'm no expert but I would guess the throttle blade is too far open. I suppose a vacuum leak could do this as well.

ULTM8Z

Do this...

Take note of the IAC steps during stable idle. Blip the throttle and then watch the IAC steps. If the reduction in steps coming back down hangs up like rpm before returning back to the original value, then you know it's the IAC that's causing the issue. After that it's jus a matter of figuring out what's making the IAC behave that way.

Dyno Don

iTrader: (7)

I too have been fighting this issue for many months.
I have changed throttle body a couple of times, I have changed the IAC several times retuned the chip a couple of times and still the problem exists.

When pulling up to a stop the idle hangs, if I wait long enough it will come down. If the car is still rolling it will never come down.
Sure would love to find the answer.

ULTM8Z

When I get home today, I'll go through and gather up all my idle settings and post it up.

Don, my car still will not idle down to 600 rpm if the car is rolling (which doesn't bother me). But when I come to a stop, it'll drop down immediately.

ULTM8Z

Ok, here's where my tune differs from a factory $8D tune (as represented by AUJP and ANHT)...

(Actually not that much is different)

In the table "IAC Manual Throttle Follower Offset vs MPH", I zeroed everything out. I think what this did was to avoid adding any IAC steps to the idle based on vehicle speed. Don, this may solve your issue.

On the tables "Idle overspeed spark retard vs idle speed error" and "Idle underspeed spark advance vs idle speed error", I zeroed those values out as well. This seemed to get rid of idle speed "hunting".

So, those two things along with setting the thottle blades to give me 0 IAC steps in neutral seems to have done the trick.

Dominic Sorresso

Is it possible that the Offset v MPH is what would cause the idle to oscillate while engine is free-wheeling and car is coasting to a stop?

ULTM8Z

I believe so, yeah.

I didn't seem to completely eliminate that (as per my earlier post). But I'm never in neutral while rolling since I have an automatic.

But when in gear, I never notice it. It effectively idles down immediately.

Dominic Sorresso