Rough Idle or vibration

1994 FORD THUNDERBIRD
110,000 MILES • 3.8L • 6 CYL • 2WD • AUTOMATIC
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SURGEIMPULSE
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I have been noticing a rough idle or vibration during idle in my car for a long time, never really any sounds. The vibration is strongest in drive or reverse, but when I switch to park or neutral it becomes much calmer.
Jun 20, 2019 at 6:49 PM
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JACOBANDNICKOLAS
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Welcome to 2CarPros.

Most times, that is the result of a low idle or a worn motor mount. There are many other things which can cause this. Lets start by looking through this link. It discusses exactly what you described. Read through it and see if anything there helps.

https://www.2carpros.com/articles/vibration-noise

Also, pay attention to idle speed. It should be near 700 when in gear. If it is a lot lower, let me know.

Joe
Jun 20, 2019 at 7:37 PM
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SURGEIMPULSE
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Thank you. I do not suspect that the culprit is misfiring as the engine sounds to be running smooth, and I am also tuning up the engine (replaced spark plugs, etc.,) and the problem still persists. Replacing the distributor cap and rotor is next up, so I will give an update once I do so. Idle in gear is right at 700 too.
Jun 20, 2019 at 8:09 PM
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JACOBANDNICKOLAS
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Welcome back:

Do me a favor, I need you to check to see if there are any engine vacuum leaks. That can cause a rough idle. Here is a link that may help. Also, a new distributor cap and wires may do the trick.

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

Let me know the final results.

Take care,
joe
Jun 20, 2019 at 10:37 PM
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SURGEIMPULSE
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I think I felt a very slight misfire at a stoplight. Not constant and happens every once in a while in idle. The distributor rotor is dirty so that might be the problem.
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Jun 24, 2019 at 1:54 PM
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JACOBANDNICKOLAS
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Welcome back:

If you take some emery paper, you can clean the rotor to see if it makes a difference. Have you tried to check for diagnostic trouble codes? Here is a link that shows how to retrieve them on a Ford OBD1 system. That may show a misfire.

https://www.2carpros.com/articles/ford-lincoln-mercury-obd1-1995-and-earlier-diagnostic-trouble-code-definition-and-retrieval

Let me know.

Joe
Jun 24, 2019 at 5:55 PM
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SURGEIMPULSE
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Currently I do not own a scanner, but I will consider getting one.
Jun 24, 2019 at 6:13 PM
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JACOBANDNICKOLAS
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Welcome back:

You don't need a scanner to get codes from this system. A small jumper wire and a basic test light will do the trick. Take a look through the link I attached.

Let me know if I can help.

Joe
Jun 24, 2019 at 6:17 PM
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SURGEIMPULSE
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Replacing cap, rotor and air filter in about a week since they really need to be replaced anyways. Will update you and scan if that does not improve the performance.
Jul 4, 2019 at 11:00 AM
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JACOBANDNICKOLAS
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Welcome back:

If they are old, hopefully that will take care of the problem. Let me know if I can help.

Take care and happy 4th.

Joe
Jul 4, 2019 at 6:08 PM