The engine idles rough at stops and low speeds?

Tiny
FIREMAN305
  • MEMBER
  • 2019 NISSAN FRONTIER
  • 4.0L
  • V6
  • 2WD
  • AUTOMATIC
  • 39,000 MILES
When changing gears from park to reverse the car vibrates. In neutral in smooths out and in drive in vibrates once again. MAF sensor went bad and was replaced once the check engine light came on. Changed the PCV valve that was failing causing the MAF sensors to be damaged. Changed the original spark plugs and coils (original plugs were not gapped properly to 0.044). The car smoothed out and the vibration stopped. The 2nd time the MAF sensor was changed the car once again started having vibration issues once again at idle. The only codes present beforehand were P0171 and haven’t come on since changing the MAF sensor. No codes now but car is having rough idling.
Sunday, February 23rd, 2025 AT 9:59 AM

5 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 50,520 POSTS
To confirm this truck has 39,000 miles. This truck must have the correct spark plugs at the right gap.

NGK Iridium IX with the part number ILZKBR7B11

gap: 1.1 mm

A rough idle condition can be a vacuum leak or low compression in one or more cylinders.

https://www.2carpros.com/articles/repairing-engine-rough-idle-issues

The P0171 code indicates that the engine’s computer has detected a lean condition on Bank 1

This can be because of a misfire @ idle. I would check for vacuum leaks first which is easy to do. Use this guide when the engine is cold:

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

Please go over these guides and get back to us.
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Sunday, February 23rd, 2025 AT 12:18 PM
Tiny
FIREMAN305
  • MEMBER
  • 3 POSTS
Yes 39,000 miles. The spark plugs I took out initially were all gapped at different measurements. I used a wire feeler gauge, and they were at 0.030-0.044. I took the car to the dealer and all they found was a small leak in a hose but other than that no findings. I have done the smoke test and no leaks were detected. Will check the brake booster hose although have had no issues braking thus far. Have used Lucas fuel injector cleaner and have cleaned the throttle body. Short- and long-term fuel trim values have improved since replacing the failing valve. The values are fluctuating. The long-term values are at 0 when accelerating but go up and down when idling. At idle the STFT for bank 1 is 8.4 and bank 2 is 4.3. The car has never turned off or stalled. Has never had issues starting.
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Sunday, February 23rd, 2025 AT 5:43 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 50,520 POSTS
The STFT for bank 1 is 8.4 and bank 2 is 4.3 seem off, they should be closer to the same. It does sound like a fuel injector issue so the cleaner might help. When you removed the spark plugs was one of them dark in color? This will be the cylinder that is having an issue.
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Monday, February 24th, 2025 AT 11:01 AM
Tiny
FIREMAN305
  • MEMBER
  • 3 POSTS
Sorry for the late reply. After having some free time to address the problem. I removed the fuel injectors and used a tester. Injectors 3 and 5 were partially clogged. Sprayed with difficulty. Got them cleaned and now the issue went away. Smooth idle now. Thank you and appreciate the help.
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Saturday, March 8th, 2025 AT 3:41 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 50,520 POSTS
Nice work! Use 2CarPros anytime, we are here to help. Thanks for letting us know, please tell a friend.
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Monday, March 10th, 2025 AT 9:18 AM

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