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Ask Chris (aka- Moose) Your Own Question
Chris (aka- Moose)
Chris (aka- Moose), Technician
Category: Ford
Satisfied Customers: 46905
Experience:  16 years experience
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2003 Ford Taurus SES 3.0 OHV,no flex stalls at idle with A/c

Customer Question

2003 Ford Taurus SES 3.0 OHV,no flex stalls at idle with A/c pressure switch connected. Disconnect pressure switch, engine runs ok at idle around 600 rpm but does not stall. Replaced IAC, no change.
Submitted: 1 year ago.
Category: Ford
Customer: replied 1 year ago.
Idle seems low, would expect 8-850 rpm under normal ops with a/c cycling on off to keep cabin static free without a/c switch turned on.
Expert:  Chris (aka- Moose) replied 1 year ago.

Welcome, I am Chris (aka-Moose)

With the climate control off and the pressure switch connected does it stall?

Can you clean the throttle body and the MAF sensor?

What is the idle speed with the IAC unplugged?

With the key on, IAC and pressure switch plugged in, back probe the IAC connectors, what voltage do you get on each wire?

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Thanks Chris

Customer: replied 1 year ago.

1. No doesn't stall with engine cold or warm. 2. Yes, did that. 3. Engine stalls when IAC is unplugged from running engine. 4. 11.9 VDC both wires to batt. neg key on engine off. Jeff

Expert:  Chris (aka- Moose) replied 1 year ago.

Thanks, ***** ***** headlight on, wipers on, rear defrost on. What is the battery voltage?

With the IAC unplugged keep the engine running by manually holding the throttle open. Adjust the throttle stop screw so it idles at 500. Then plug i nthe IAC. Does that help?

Customer: replied 1 year ago.
1. 14.1 VDC, 2. IAC unplugged, rpm adjusted to 500 causes engine to idle @1050 when iac is plugged back in. Reattach ac pressure switch, cycling of a/c clutch causes engine to drop to 600 with clutch engaged and 1050 when off cycle. Engine very rough @ 600 with a/c engaged so returned adjustments to previous.
Expert:  Chris (aka- Moose) replied 1 year ago.

Thanks its looking like the computer is controlling the IAC incorrect. Back probe and monitor the voltage at the IAC valve WH/LB wire at hot idle. It should be 8.4 DC volts.

Customer: replied 1 year ago.
9.1 to 9.3 vdc to batt neg at hot idle rpm 625, cold idle 8.2 to 8.3 vdc rpm 1000-1100
Expert:  Chris (aka- Moose) replied 1 year ago.

Thanks, ***** ***** results we know the computer is not controlling the IAC correct. The voltage at hot idle needs to be lower to increase the idle speed. Will your scan tool tell you if the MAF reading and TP readings are accurate?

Customer: replied 1 year ago.
Doubtful, can read codes only. Cheap actron scanner sold by advance auto, not as good as your snap-on or equal. Strangely, not getting any codes yet. Left a/c pressure switch plugged in on Fridays drive home from work 25 miles, topped off fuel tank, engine stumbled a few times down to about 500 rpm but didn't stall. Drove balance of the way home and pulled a/c pressure switch back off. Called local salvage yard, they relate there are about seven pcm choices so numbers are crucial for proper selection. $75.00-100.00 if they have the correct one. Would you try a used one?
Customer: replied 1 year ago.
Wouldn't know the correct readings for TP (throttle position sensor or MAF anyway or how to test and don't have access to the info.
Expert:  Chris (aka- Moose) replied 1 year ago.

A used PCM will be fine but the part number must match and it has to be programmed once in your vehicle.

Hot idle MAF voltage should be 0.6-09 Light Blue/Red

Hot idle TP voltage should be 0.53-1.27 Gray/White wire

Customer: replied 1 year ago.
PCM must be programmed by Dealer or must relearn drive characteristics by owner? Have you personally replaced with used pcm? I don't know what's involved for used pcm to restore function and operating parameters, Thanks
Expert:  Chris (aka- Moose) replied 1 year ago.

You have to have a dealer level tool used to program it or the PATS anti theft system will not allow the engine to start.Replaced hundreds of PCMs. It takes about 5 days of use for a replacement PCM to fully learn you and your cars driving characteristics.