1989 5.0 idle speed - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 10 Old 09-09-2019, 09:39 AM Thread Starter
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1989 5.0 idle speed

Guys,

Working on a 1989 5.0. I set the idle to 750 with the IAC disconnected (engine hot). Then I disconnected the battery for several minutes to clear out the memory. Hooked everything back up and got the idle right at 750 where I want it.

However, after test driving for 10 or 15 minutes, the idle is back at 1000. I can disconnect the IAC and it drops.

Seems like the ECU is using the IAC to speed up the idle.

A guy at work suggested cleaning the IAC. I have not tried that yet as it seems to be working...i.e no surging, just a high idle speed. Question though...I note that you can blow through the valve when it is off the car. Does that indicate it has a problem? Shouldn't it be closed with no power to it so it wouldn't pass low pressure air?

Other than this, the car is running great.

Phil

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post #2 of 10 Old 09-09-2019, 11:14 AM
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ECM controls idle

There used to be a ‘do not adjust label’ under the hood to inform people of this

If this is a totally stock engine, you can try the idle reset procedure designed for factory engines, ie stock TB and MAF....

It is normal for the valve NOT to be totally sealed


89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #3 of 10 Old 09-09-2019, 11:31 AM Thread Starter
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Quote:
Originally Posted by indy2000 View Post
ECM controls idle

There used to be a ‘do not adjust label’ under the hood to inform people of this

If this is a totally stock engine, you can try the idle reset procedure designed for factory engines, ie stock TB and MAF....

It is normal for the valve NOT to be totally sealed
Good info. So is the idle reset procedure different than what I described above...i.e. setting to 750 with IAC disconnected and power cycling the ECU?

Phil
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post #4 of 10 Old 09-09-2019, 03:47 PM
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its not really a idle reset, its a stop reset

in stock form, you get the engine nice and hot

disconnect the SPOUT, idle is actually set by timing by the ecm the IAC is for transitions and loads, then disconnect the IAC

get the engine to idle as low as posssible, 500-550rpm by backing the adjusting the stop

then erase the KAM, disconnect the battery step on the brake pedal

restart, goose the engine a few times

then wait for about 100 start cycles at different conditions, idle will learn


this may work or not, its only chance is with a totally stock engine.

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #5 of 10 Old 09-10-2019, 08:30 AM Thread Starter
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It's near stock...but not totally.

Very interesting info on timing setting the idle.

So...this 1989 has 160,000 miles on it. The engine was rebuilt about 130...but I just reused the stock distributor. Any chance the distributor is more the issue here?

Phil
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post #6 of 10 Old 09-10-2019, 09:48 AM
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if it runs, doubtful the dist is an issue

what is not stock??

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #7 of 10 Old 09-10-2019, 02:48 PM Thread Starter
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GT40P Heads. E-Cam.

Running a 1994 MAF. I did have a larger TB installed, but went back to stock to help this idle issue. It did help, as the old (non-stock) TB had an air leak past the throttle body blade.

Phil
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post #8 of 10 Old 09-10-2019, 04:33 PM
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YOU CAN TRY the reset procedure

If it doesn’t work, you will need a ecm recalibration, to account for the different airflow at idle

I am not sure, what you mean by air leaking past the blade, as they have to

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #9 of 10 Old 09-11-2019, 06:38 PM
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Garage
Idle reset ...https://www.corral.net/index.php/tec...ment-and-reset

89 Reggatta blue,Trickflow Intake,
1in spacer.65mmTB,GT-40 aluminum heads(X303),3000 Dynamic Converter, Motorcraft plugs 32c's ,E-cam,24lbs Injectors,Pro-M 76mm Mass air , AOD,shift-kit, modified valve body, 410 gear, Eaton
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post #10 of 10 Old 09-11-2019, 08:09 PM
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that is completely useless and will lead to other drivability issues


89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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