trouble shooting

[Curious Hound]

You might still have the vacuum diagram on a sticker at the front of the engine bay, usually in the radiator support.

 

[pcav]

If you unplug them the engine will start running rough or stall because you are creating a huge vacuum leak. However, you can unplug individual lines at the vacuum port on the manifold and put a cap over the port to prevent a vacuum leak. You can buy vacuum line caps at most auto parts stores. I'm not familiar with the ports on a 92, but I'm assuming there are normally a few or more vacuum lines connected to several ports. You can disconnect them one by one, but a cap over the port on the manifold and take it for a test drive. If you find one of the lines may have a leak you may have to check for a T in that line that splits off for different devices/sensors. These tests may turn on the check engine light on OBDII vehicles (95 and later). I don't know if that is the case on a 92. Don't overlook the possibility of an intake manifold leak, a leak in the power brake booster diaphragm, leaking throttle plate hinges, or anywhere along the air intake plenum between the air filter and where it connects to the throttle intake, in addition to the PCV valve and its tubing that connects to the intake manifold.

This website has vacuum diagrams. Maybe someone who has a 91 thru 94 4.0L can tell you, or post a picture of the vacuum line port locations.

https://www.therangerstation.com/ho...tems/ford-ranger-engine-vacuum-hose-diagrams/

There are other issues that can cause your problem. Just do a search for surging engine or high idle. But, checking for vacuum leaks is the first step.

Thank you so much

 

[19Walt93]

It wouldn't hurt to start by removing and cleaning the IAC valve. That's idle air control if you haven't heard the term. Cleaning the throttle body is a good idea,too, just make sure to use throttle body cleaner and not carb clean.

 

[pcav]

Not exactly...

I like propane... carb cleaner will work also.

Lightly release either on suspect areas below the throttle plate while running and note the areas that change engine RPM.

If you unplug them the engine will start running rough or stall because you are creating a huge vacuum leak. However, you can unplug individual lines at the vacuum port on the manifold and put a cap over the port to prevent a vacuum leak. You can buy vacuum line caps at most auto parts stores. I'm not familiar with the ports on a 92, but I'm assuming there are normally a few or more vacuum lines connected to several ports. You can disconnect them one by one, but a cap over the port on the manifold and take it for a test drive. If you find one of the lines may have a leak you may have to check for a T in that line that splits off for different devices/sensors. These tests may turn on the check engine light on OBDII vehicles (95 and later). I don't know if that is the case on a 92. Don't overlook the possibility of an intake manifold leak, a leak in the power brake booster diaphragm, leaking throttle plate hinges, or anywhere along the air intake plenum between the air filter and where it connects to the throttle intake, in addition to the PCV valve and its tubing that connects to the intake manifold.

This website has vacuum diagrams. Maybe someone who has a 91 thru 94 4.0L can tell you, or post a picture of the vacuum line port locations.

https://www.therangerstation.com/ho...tems/ford-ranger-engine-vacuum-hose-diagrams/

There are other issues that can cause your problem. Just do a search for surging engine or high idle. But, checking for vacuum leaks is the first step.

I didn't find any leaks

 

[pcav]

It wouldn't hurt to start by removing and cleaning the IAC valve. That's idle air control if you haven't heard the term. Cleaning the throttle body is a good idea,too, just make sure to use throttle body cleaner and not carb clean.

Still no positive results