Engine misfire

Hi,

It sounds like you have either a vacuum leak or there is an issue with the idle air control valve (IAC). The IAC is responsible for maintaining idle speed. When you put it in gear or turn the AC on, do the RPM drop?

First, and I have a feeling you may have already done this because of the brake booster replacement, check for engine vacuum leaks.

Here is a link that explains how that is done:

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

Next, here are two links. One explains how to service the IAC and the other how to replace one. The IAC is located on the throttle body.

https://www.2carpros.com/articles/idle-air-control-valve-service

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

If the check engine light is staying on when the engine is running, you really should have the computer scanned to retrieve diagnostic trouble codes that will help identify where the problem is coming from. Here is a quick video showing how that is done:

https://youtu.be/YV3TRZwer8k

I realize most people don't own a scanner, but most parts stores will do it free of charge or lend/rent a scanner to you.

Let me know if any of this helps or if you have other questions.

Take care,
Joe

Hi,

Before you replace it, try cleaning the present one. Here are the directions from Alldata:

2005 Buick Allure (CANADA) V6-3.8L
Throttle Body Cleaning Procedure
Vehicle Powertrain Management Fuel Delivery and Air Induction Throttle Body Service and Repair Procedures Throttle Body Cleaning Procedure
THROTTLE BODY CLEANING PROCEDURE
THROTTLE BODY CLEANING PROCEDURE

REMOVAL PROCEDURE
1. Disconnect the air intake ducts from the throttle body.

CAUTION: Turn OFF the ignition before inserting fingers into the throttle bore. Unexpected movement of the throttle blade could cause personal injury.

2. Inspect the throttle body bore and the throttle valve plate for any deposits. It is necessary to open the throttle valve in order to inspect all of the surfaces.
3. Clean the throttle body bore and the throttle valve plate by using a clean shop towel with Top Engine Cleaner, GM P/N 1052626 (Canadian P/N 993026) or AC-Delco Carburetor Tune-Up Conditioner, P/N X66-P, or an equivalent product.

NOTE: Do not use any solvent that contains Methyl Ethyl Ketone (MEK). This solvent may damage fuel system components.

INSTALLATION PROCEDURE
1. Connect the air intake ducts to the throttle body.
2. Inspect for air leaks.

________________________________________

Let me know if that helps. Also, let me know if you checked for vacuum leaks.

Take care,
Joe

If you cleaned the throttle body and there are no leaks, my first suspect is the IAC. However, on this vehicle, there isn't an IAC at least in the true definition of an IAC. In this case, there is a throttle actuator control module. I attached a picture of its location.

Let me know if you have checked wiring and connections there.

Joe

Hi,

Yes, low voltage can lead to a misfire along with other issues. Here is a link that explains how to test the alternator. Check to make sure it is producing enough power.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Let me know what you find.

Joe

Happy to hear you got it fixed, and you are very welcome. Let us know if you need help in the future or ever have questions. We'll be here.

Take care,
Joe

Hi,

If the lights only slightly dim, I wouldn't be too concerned. It isn't uncommon. As far as vacuum diagrams, I attached the three schematics I have. Let me know if they help.

Let me know what happens when you take the belt off.

Take care,
Joe

Rather than making the purchase at this point, can you get your hands on a live data scanner and let me know what both the short term and long term fuel trims are? If you can get that, I can tell if there is a problem with low fuel pressure, vacuum leak, faulty pressure regulator and so on. Also, you mentioned that the check engine light is back on. What code is present?

I would feel better knowing the code and the fuel trims before having you spend the money and replacing the TB. If, however, you chose to replace it first, here are the directions. The attached pics correlate with the directions.
________________________________________________________________
2005 Buick Allure (CANADA) V6-3.8L
Throttle Body Assembly Replacement
Vehicle Powertrain Management Fuel Delivery and Air Induction Throttle Body Service and Repair Procedures Throttle Body Assembly Replacement
THROTTLE BODY ASSEMBLY REPLACEMENT
THROTTLE BODY ASSEMBLY REPLACEMENT

REMOVAL PROCEDURE

pic 1

1. Partially drain the cooling system. Refer to Draining and Filling Cooling System.
2. Remove the fuel injector sight shield.
3. Remove the air cleaner intake duct.
4. Disconnect the throttle body electrical connector.
5. Remove the throttle body nuts (4) and the bolts (5).
6. Remove the throttle body assembly (1).
7. Clean the throttle body gasket mating surfaces.

NOTE: Do not use solvent of any type when cleaning the gasket surfaces on the intake manifold and the throttle body assembly, as damage to the gasket surfaces and throttle body assembly may result.

Use care in cleaning the gasket surfaces on the intake manifold and the throttle body assembly, as sharp tools may damage the gasket surfaces.

INSTALLATION PROCEDURE

pic 2

1. Install the new gasket.
2. Install the throttle body assembly (1).
3. Install the throttle body bolts (5) and the nuts (4).

NOTE: Refer to Fastener Notice in Service Precautions.

Tighten the bolts and the nuts to 10 N.M (89 lb in).

4. Connect the throttle body electrical connector.
5. Install the air cleaner intake duct.
6. Install the fuel injector sight shield.
7. Fill the cooling system. Refer to Draining and Filling Cooling System.

__________________________________
Let me know.

Joe

That's the best of the best. LOL Those are the tools needed when you do it every day.

As far as the misfire, was it one specific cylinder or a random misfire (P0300)? Are you certain there are no vacuum leaks at the intake manifold itself?

As far as the car, they are good vehicles, but everything gets old. I have an 2005 A4 that I love, but it's getting to that point. Two heater core hoses (approximately 18" long small rubber hose, cost 198.00, and I get to put them on. UGH! LOL You vehicle's heater hoses would be under twenty dollars in parts. I'll trade you. LOL

Let me know.

Joe

Don't forget the hidden vacuum leaks. IE brake boosters, EVAP purge valves.

Were the booster hose and check valve both new?