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Pete , Buick Technician
Category: Buick
Satisfied Customers: 23560
Experience:  17 years Buick Technician experience and training.
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2005 Buick lesabre: intermittant rough idle..3800 engine, 114k miles.

Resolved Question:

2005 Buick Lesabre intermittant rough idle. 3800 engine, 114K miles. No codes. Replaced usual suspects from normal wear: spark plugs, wires, fuel pressure regulator, serpentine belt, fuel filter, air filter. Checked resistance on fuel injectors, all > 12 and within 0.5 of each other. Intake manifold gasket replaced while under warranty 71K miles. No visible coolant leaks in oil or external either. Uses a quart of oil every 2K miles. No other vacuum leaks I could find. Car has tons of power, gets good gas mileage, runs smooth on the freeway.
Here's what is unusual. If I pour fuel system cleaner in gas tank the problem goes away until the next tank (without additive). Seems real to me but perhaps just my imagination. Any suggestions?
Submitted: 5 years ago.
Category: Buick
Expert:  Pete replied 5 years ago.
Hello,I will be glad to try and assist you with this,Welcome to Just Answer.


It sounds like you have covered quite a few components that are usually possibilities of this kind of fault.One thing that may be at fault judging by what has been done,also be adding the cleaner to the tank is one or more fuel injectors not spraying or atomizing properly.

The injectors will test good doing a resistance test but o find out if one or more is spraying or atomizing improperly.

This test needs done using a fuel pressure gage and a scan tool or fuel injector pulse tool to pulse each injector one at a time to observe the fuel pressure drop of each one.They should all drop very close to the same,if one or more is found 1.5 to 2 psi off then the rest of them then it is at fault.

In some cases a shop or dealer can install a fuel injection cleaning machine to clean the injectors and in other cases the injector or injectors affected would need replaced.

Let me know if you need anything else,click accept if you feel satisfied with your answer as this is how I get credited for my time,Thanks Pete!
Pete, Buick Technician
Category: Buick
Satisfied Customers: 23560
Experience: 17 years Buick Technician experience and training.
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