Checking and Cleaning – A Guide to A Detailed Tune up

In the previous article, we have covered a basic tune up procedure, explaining what needs to be done to keep your engine in good shape. While these steps are great as general preventive maintenance, there are additional things you can do to make your car run even better.

Inspecting the fuel trims

When performing a detailed tune up, fuel trim values should be the first thing to check and analyze. This data is one of the vital indicators, showing how the engine is running. All modern cars come from the factory with engines that are balanced when it comes to air and fuel mixture. Based on the data from various sensors, the PCM in your car knows how much air is entering the engine and calculates how much fuel it needs. Some of the most important sensors are the Mass Air Flow (MAF) sensor, Intake Air Temperature (IAT) sensor, and Throttle Position (TP) sensor.

Auto mechanic doing an engine tune up

However, many things outside the PCM control can affect the air-fuel mixture. As this can cause an engine to run in either lean or rich, an exhaust oxygen sensor monitors the exhaust gas content. This additional sensor helps the PCM to fine-tune the air-fuel mixture when issues out of its control arise. Depending on the data from the O2 sensor, the PCM will adjust the amount of fuel injected. Fuel trim is the name for the amount of adjustment. They are helpful when assessing how the engine is running and pinpointing potential issues.

Cleaning the MAF sensor

The MAF sensor uses a feature called ‘hot wire’ to calculate the amount of air entering your engine. This value is the first step in adjusting the amount of injected fuel. No matter the make and model of your car, you can find this sensor between the air filter and throttle body assembly. Although protected from the elements, a hot wire element can get contaminated with dirt and dust over a long period. This will cause inaccurate air flow readings and result in a lean running engine. especially on a car that hasn’t had a tune up in a long time. Some symptoms you may experience are rough engine operation, lack of power, and hesitation during acceleration.

Mass air flow sensor

Cleaning the MAF sensor is a fairly simple job, but make sure you use nothing but a MAF cleaner. This spray contains a fluid specially designed to dissolve dirt buildups without damaging the sensitive hot wire.

Cleaning the throttle body

The throttle body in your car controls the amount of air entering the engine. It is in a direct link to the gas pedal, either by a cable or by a servo motor, and it opens and closes accordingly. Much like the MAF sensor, internal throttle body parts are exposed to small amounts of dirt and dust. To make things worse, most cars have a crankcase ventilation connected to the throttle body. Oil fumes and droplets accumulate inside the throttle body. With time, this can jam moving parts such as throttle plate, or prevent it from closing all the way and even decrease the airflow. Some symptoms you may notice are rough or high idle and a sticky gas pedal.

Auto mechanic doing a tune up on a throttle body

Many cars have an idle air control (IAC) valve, which allows the air to bypass the throttle plate at idle. When you press the gas pedal, the throttle plate opens up to allow air to enter the engine. However, as this plate is closed at idle, the idle air control valve serves as a bypass. It lets the air go from this side of the throttle plate to another and controls this flow. If this valve fails, you will experience hard starting, rough idle, and stalling. Similar will happen if the passages get clogged up with carbon buildup.

Cleaning the throttle body is a fairly easy job and should be performed at every tune up. All you need is some throttle body and air intake cleaner spray and a clean rag. Spray the cleaner inside the throttle body and all the air passages within. Pay special attention to throttle plate edges, as it needs to be clean to seal when on idle. If your car has an idle air control valve, remove and clean it.

Cleaning the EGR valve

An EGR system is an emission control device found in most modern cars. It lowers emissions by returning a portion of exhaust gases into the engine intake. The assembly is simple, with several pipes and an EGR valve, which controls the flow. As the exhaust gases are full of soot and other particles, EGR can get clogged with time. This blocks the exhaust flow. Other than that, carbon deposits can cause an EGR valve to get stuck in either an open or closed position. This can cause many driving issues, ranging from rough idle and stalling to pinging and strong detonations under hard acceleration.

Exhaust Gas Recirculation (EGR) valve

Depending on how clogged the EGR valve is, there are several possible solutions. The easiest and quickest way is to use an EGR valve cleaning fluid. This is a specially designed solvent that you spray into the intake of your engine while it is running. The procedure does not require much expertise or any special tools. However, if the build-up is excessive, the only option is to remove and clean the valve. You will need several chisels and wire brushes for this job, and a can of EGR or carb cleaner.

Checking for vacuum leaks

Checking for vacuum leaks is a very important step when doing a detailed tune up. A vacuum leak is any amount of unmetered or unmeasured air that enters your engine. As we already explained, the car PCM uses data from the MAF sensor to calculate the optimum air-fuel mixture for various driving conditions. This means that all air hoses, vacuum lines, and various intake manifold gaskets must be in good shape and air-tight. We consider any air that escapes into the system behind the MAF sensor a vacuum leak. This will throw off the air-fuel mixture and cause performance issues. These issues can vary depending on the size and some degree location of the vacuum leak.

A small vacuum leak will cause either fluctuating or high idle. The main culprit for this are the various vacuum lines, coming out of the intake manifold. It is common for these lines to get dry and brittle and start developing cracks through which the air leaks lines into your engine. In general, small vacuum leaks are more noticeable at idle when the engine is cold. On the other hand, a large vacuum leak will cause a rough and low idle. Besides, it may be hard or impossible to start a car. Besides that, you might experience hesitation or bogging down when you try to speed up. In most cases, a cause for a large vacuum leak cause is a broken intake hose or a bad manifold gasket.

About Bojan P

My name is Bojan - I am a car enthusiast, specialised in the vehicle diagnosis, repair and maintenance with 10 years of practical, hands-on experience. In addition, I have a Masters degree in mechanical engineering.

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