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Ron, ASE Certified Technician
Category: Mercury
Satisfied Customers: 35601
Experience:  ASE Certs and Ford Certs
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I have a 2002 Mercury Mountaineer. I was having problems with

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I have a 2002 Mercury Mountaineer. I was having problems with the engine idling high and the car would go about 30 MPH at idle. This problem was intermittent. I just replaced the Idle Air Control and it will still idle high and when I rev the engine it will stay at 2000 rpm for a few seconds and then return to about 750 rpms and now since changing the IAC it almost stalls. I never had this problem prior to changing the IAC.

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Customer: replied 4 years ago.
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The problem you are describing is in most cases caused by eaither a failing IAC or a bad TP (throttle position ) sensor and because you have replaced the IAC, I would suspect the TP sensor is faulty and needs to be replaced.With the idle set at 550-600 RPM, typical TPS voltage should be 0.9-1.0 volts, but not more than 1.0 volt. Scan tool data should read closed throttle. I would start with replacing the TP sensor and when doing so, remove the negative battery cable to clear idle strategy for about 10 minutes. After the strategy has been cleared, test drive the vehicle for an idle relearn and retest.

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Customer: replied 4 years ago.
I changed the tp sensor and am still having the same problem.
Did you disconnet the Negative battery canle before the repair.

Does the idle speed drop if you unplug the IAC?
Customer: replied 4 years ago.
Yes. I disconnected before the repair. So here is what is doing...

When I start the car it will jump up to 2000-2500 rpm and stay there for a few seconds before dropping to about 500rpms where it will sputter. When I disconnected the iac it does not stick at 2000-2500 rpm like when it's plugged in but if I don't rev the engine it will sputter and stall. When I drive and have it up to speed it seems to be normal until I have to stop... Then it sputters and sounds like its going to stall and lurches forward. If I start from idle and keep my foot of the gas it will accelerate to about 33mph at around 1500 rpm. Prior to changing the iac... I did have this problem but now it seems worse as I never had as big of a problem with the sputtering and lurching when stopping.
The IAC signel come from the PCM (computer) and if replacing the TP sensor and making sure the voltage is okay on it then I would suspect the PCM has lost its ability to control idle speed thru the IAC, if this is the cases You may need to have the PCM re -flashed with latest software.
Customer: replied 4 years ago.
Can this only be done at the dealer?
Unless you have acess to Ford and there scan tool then yes its has to be done by the dealer. Most dealers charge right at 1 hour to do so.
Ron, ASE Certified Technician
Category: Mercury
Satisfied Customers: 35601
Experience: ASE Certs and Ford Certs
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