I suspect you have an idle circuit issue. When the thottle is closed, the throttle valve is almost closed (like 95%). The linkage on the throttle body is against the hard stop.
SO, when idling you need a way to let enough air into the engine to maintain an idle speed. The IAC, Idle Air Control valve is the way you do that and the engine computer controls the rate of air flow.
Sometimes it gets plugged up so you can clean it with a little carb cleaner. Might have to take it apart.
Also, you have a MAF, Mass Air Flow sensor that tells the computer how much air is flowing through the air cleaner intake at any time. The sensor gets coated with varnish and vies a false reading. Clean it gently with carb cleaner and a toothbrush.
Other than that, I would go to an auto parts store that can run a computer scan for free to see if you have any fault codes stored. They will tell you next stpes.
I assume you 2.0L SPI engine & not Zetec.
Idle Air Control (IAC) Valve —2.0L SPI
Removal
- Disconnect the idle air control (IAC) valve electrical connector (air cleaner outlet tube removed for clarity).
- Remove the IAC valve.
- Remove and discard the IAC valve gasket.
Mass Air Flow (MAF) Sensor
Removal
- Remove the air cleaner outlet pipe.
- Disconnect the mass air flow (MAF) sensor electrical connector.
- Remove the MAF sensor.
clean element inside carefully
PS. A good running engine makes for a better running transmission
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