Rough idle

Hi and thanks for using 2CarPros.

Many things can cause this type of issue. Often times an engine vacuum leak can be an issue. Most commonly on these vehicles is a vacuum hose which routes from the rear of the throttle body and goes to a 90 degree bend. The bend will dry rot and cause a leak. Additionally, there is a component called an idle air control valve (IAC) which controls idle speed. If that is plugged or not working, it will cause the engine to stall, but if you place it in neutral and it idles fine, that wouldn't be a prime suspect.

Here is a link that discusses engine stall at idle. Take a look through it to see if it is helpful.

https://www.2carpros.com/articles/stall-at-idle

Here are links that discuss the IAC and how to check for a vacuum leak:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

Next, if there is a problem with the fuel pressure regulator which is allowing pressure to be too high, it can cause this type of problem. To check this component, you would need to perform a fuel pressure test along with checking the regulator. Here is a link that shows how that is done:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Before you go through the fuel pressure test, locate the fuel pressure regulator which is located on the fuel rail. There is a vacuum hose attached to it. Remove the vacuum hose and confirm there is no raw fuel in it.

Here are the directions for removal and replacement of the regulator. The attached pictures correlate with these directions. I attached these directions in case you determine the regulator is the problem.

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FUEL PRESSURE REGULATOR

REMOVAL

WARNING:
- Do not smoke or carry lighted tobacco or open flame of any type when working on or near any fuel-related components. Highly flammable mixtures are always present and may be ignited. Failure to follow these instructions may result in personal injury.
- Fuel in the fuel system remains under high pressure even when the engine is not running. Before working on or disconnecting any of the fuel lines or fuel system components, the fuel system pressure must be relieved. Failure to follow these instructions may result in personal injury.

1. Relieve the fuel pressure.
2. Remove the upper intake manifold.

Picture 1

3. Remove the fuel pressure regulator.
1 Disconnect the fuel pressure regulator vacuum hose.
2 Remove the snap ring.
3 Remove the fuel pressure regulator.

Picture 2

4. Remove and discard the fuel pressure regulator O-ring seals.

INSTALLATION

1. CAUTION: Use O-ring seals that are made of special fuel resistant material. Use of ordinary O-ring seals can cause the fuel system to leak. Do not reuse O-ring seals.

NOTE: Lubricate the new O-ring seals with clean engine oil to aid installation.

To install, reverse the removal procedure.

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I realize this is a lot of information. However, since there are no diagnostic trouble codes, it requires a lot more diagnosis. There are other things that will need checked if these things don't prove to be an issue. From experience, your description sounds like either a vacuum leak, IAC is plugged, or fuel pressure it too high.

Feel free to ask me questions if you have them. Also, let me know what you find.

Take care,
Joe

Happy to help. Let me know if you have other questions. Also, after I replied yesterday, another thought came to mind. There is a coolant temperature sensor the computer uses to determine the air fuel mixture injected into the engine. If the sensor is sending an incorrect temperature reading, the mixture will be off. For example, if the computer is told it is -40 degrees outside but in reality it is 75 degrees, the fuel mixture will be much too rich.

Pay attention to when it is happening if the exhaust is putting out black smoke. That would indicate too much fuel is getting into the engine. Also, if you have access to a live data scanner, you can actually check what temperature the sensor is telling the computer and make a determination if it is accurate.

Let me know what you find or if you need help.

Take care,
Joe

No problem. If you find that you do have questions or need anything, let me know.

Take care and if you have the chance, I would love to know what the cause was.

Joe

I think I know what is wrong. You have a major vacuum leak. I need you to check a few specific hoses. First, you will see where two hoses attach to a component above and to the left of the brake booster. Closely check both hoses for damage, dry rot, or anything that could cause a vacuum leak. Next, along the rear of the engine are other larger vacuum hoses which commonly dry rot, melt... and create a vacuum leak. Check all hoses back there. Also, check the large vacuum hose that runs from the rear of the intake to the valve cover on the passenger side (PCV). Some of the hoses are somewhat hidden under the cowl, so take your time. If you look at pictures 1 and 2, it shows the purge solenoid which is the part I referred to which is to the left of the brake booster. You can see the two hoses that attach. Follow them all the way back to the intake. In picture 2, the black arrows are pointing to the hoses. Picture 1 is the same part from a different view. I added it because it shows a portion of the brake booster to help you locate it.

Now, here is a link that shows how to check for a vacuum link using starting fluid. If you choose to use this procedure, make sure to follow the directions. The bottom line is carburetor cleaner is flammable. Make sure to avoid spraying it onto anything that is extremely how such as an exhaust manifold.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Also, if you open the hood and start the engine, you may be able to actually hear the leak. If you do hear it, gently move around the vacuum hoses I mentioned to see if there is a change in the sound.

Let me know what you find and I feel confident this is the problem.

Take care,
Joe

Welcome back:

Were the specific hoses I mentioned checked?

Let me know.

Joe

Not a problem, Daniel. My father was a union mason and taught me a lot about stone work. I remember well him driving a lot for work. I know construction isn't easy!

Let me know. I have to be honest, I feel he is missing something.

Take care,
Joe

Okay, that doesn't sound right. The code is for a lean mixture. Did he tell you it's extremely rich? That's the opposite of what should be happening. And, it is related to bank 1. Also, is this a natural gas vehicle? Take a look at picture 1. The code is related to a lean mixture.

Happy to help. Let me know what the other person says. I am really interested in knowing.

Take care and have a nice weekend.

Joe

Wow.. I still feel it is a vacuum leak issue. However, I may be wrong. Anytime there is a lean mixture, it is either fuel pressure is low, the injectors are plugged, or there is a vacuum leak. If I recall, pressure was tested. As far as injectors, the chances of all eight being partially plugged is slim. That leads to a leak. Did they check for a leak using carburetor cleaner?

Take a look through this link:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know. It may have to go to a Lincoln dealership.

Joe