Erratic idle

TEXLEE

MEMBER
1998 MERCURY MOUNTAINEER
5.0L
V8
2WD
AUTOMATIC
315,000 MILES

I can start the truck it will run fine going somewhere then shut it off. Come back to start the truck a few minutes later and it starts but runs rough like 3 cylinders firing rough. I was able to apply throttle and sometimes it will clear up and run fine others times it can take several attempts to get it to idle and run correctly. Today was the same thing but with the truck running very rough I opened the hood latch and when I did it started to run normal. I am thinking grounds or an electrical issue perhaps even an anti-theft system fault. Any ideas?

Wednesday, June 16th, 2021 AT 10:01 AM

1 Reply

JACOBANDNICKOLAS

MECHANIC
110,055 POSTS

Hi,

That is a tough one. The hood opening really doesn't make sense to me other than it may have simply been a coincidence. Has that ever happened in the past? When it is running rough, have you ever noticed gray or black smoke coming from the exhaust?

Based on the symptoms, I don't feel it is related to the anti-theft. It could be a ground, but that is even a stretch. Do me a favor. Read through this link and let me know if it seems to mirror what you experience.

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

Also, if the check engine light is staying on while the engine is running, have the computer scanned. Here is a quick video showing how it's done:

https://youtu.be/YV3TRZwer8k

I realize most people don't own a scanner, but oftentimes a parts store will check it free of charge.

Let me know.

TaKe care,

Joe

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Thursday, June 17th, 2021 AT 9:49 PM