Symptoms Of A Bad Intake Manifold Gasket And Replacement Cost

You probably haven’t ever thought too much about your intake manifold gasket.

To be honest, I haven’t either, and I’ve never come across a car where this has been directly diagnosed as the root cause of a problem.

Still, like anything on your vehicle, they can fail. If yours does, you might notice some of the symptoms I’ve listed in this guide.

I’ve also broken down the cost for you if a mechanic finds that the intake manifold gasket is your issue.

Related Terminology

Before we get into the nitty-gritty, I’d like to clarify a few sensor names. I’ll use them throughout this guide, so they’re important to have a basic understanding of.

• MAF sensor – in scientific terms, the mass air flow sensor detects air mass flow rate.
• MAP sensor – the manifold absolute pressor sensor reads the density of this air.

These sensors both sit in the intake manifold. They work together to calculate how much air is entering the cylinders.

What Is An Intake Manifold Gasket?

An intake manifold gasket seals the space where the air passes from the manifold and into the engine (at the cylinder head).

Like any gasket, they prevent anything from getting in or out.

This means there should be consistent internal pressure throughout the intake, as measured by the MAF and MAP sensors. Of course, this pressure varies depending on how much you push the accelerator pedal.

The intake manifold gasket’s main job is to keep the atmospheric air out of the engine. Without it, air would be sucked into the chambers through the tiny gaps between the manifold and cylinder head.

The result is too much air in the engine and a lean air-fuel mixture.

These days, most intake manifold gaskets are made of hardened rubber or silicone. They often have a metal (aluminum) frame.

You might find a few bare metal ones, although these tend to be limited to classic cars.

Bad Intake Manifold Gasket Symptoms

Here are what I’d consider the most common symptoms of a leaking intake manifold gasket.

All of these symptoms only apply when the engine’s running. If it’s off, you won’t notice anything different.

Check Engine Light

The Check Engine light activates as soon as the sensors in your vehicle detect an anomaly.

When this happens, the ECU stores a diagnostic code. This can be viewed via an OBD II code reader or scanner. I advise paying for the garage to check it using their machine because cheap models have been known to wipe the ECU completely. Not good.

Here are some codes you might expect to see if you have a leaking intake manifold gasket.

• P0171
• P0174
• P0300 through P0312

Never ignore a Check Engine light!

Hissing Sound

Air shouldn’t be able to get past the intake manifold gasket. When it warps or cracks, this leads to a hissing sound.

The engine creates a pressure difference; there’s a vacuum within the cylinders. That’s how air is always automatically sucked in.

When a manifold gasket leak develops, air doesn’t just come through the manifold and filter. It also sneaks in past the gasket.

For this reason, the MAF and MAP sensors don’t detect it.

Because these cracks or warps are tiny, the air channels through a very small space. That’s what creates that hissing sound.

Rough Idle

This, along with the symptoms below, is related to the air-fuel mixture and confused ECM.

As I explained earlier, a leak at the intake manifold gasket creates a lean air-fuel mixture because the MAF and MAP sensors can’t detect the extra air. The result is an inefficient combustion process when the spark plug fires.

You might feel your engine struggling at any rev range or speed, but it’s often most pronounced at idle. It might even stall.

Hard Start

For the same reason, you might notice your car taking longer to start.

The MAF and MAP sensors don’t detect the extra air passing past the gasket. Thus, the actual air-fuel ratio is leaner than the ECM intends.

When your engine starts, it needs a rich mixture (more fuel in relation to air). This helps it get going and warm up faster.

That’s why your car always smells more heavily of gas when you first start it.

If this mixture is leaner than it should be, the engine will find it more difficult to start.

This issue could also be caused by an old battery or any number of different problems.

Limp Mode

Limp mode is when your car goes into a self-protect mode. Acceleration and speed will be dramatically limited, so your vehicle doesn’t damage itself.

It’s annoying but clever and sensible.

A leaking intake manifold gasket could cause limp mode to activate. In short, the engine isn’t operating at peak efficiency because there’s too much air in relation to fuel.

However, your car doesn’t know why that is. It’s measured the air passing through the manifold (MAF and MAP), but it can’t account for the extra leaking past the gasket.

The ECM may assume there’s a more serious problem with something else. Limp mode might activate as a precaution.

Coolant And Oil Problems

I’ve grouped all these together because they usually only apply to V-engines. If you have a V6 or a V8 (or something even larger!), pay particular attention.

In V-engines, the intake manifold usually sits across the center of the ‘V’. Coolant passages often flow through it.

As a result, the manifold gasket must also prevent this liquid from getting into the intake ports.

As far as I’m aware, the intake manifold gasket has nothing to do with coolant in most Inline engines.

If the intake manifold gasket in a V-engine develops a leak, you might notice any of the following symptoms:

• Low coolant levels
• White smoke from your exhaust
• A coolant leak

As usual, the severity with which this happens depends on the significance of the leak.

Intake Manifold Gasket Replacement Cost

So, how much does a replacement intake manifold gasket cost?

If you take your car to a shop (which I recommend), the total cost will likely be around $250. It might go slightly higher.

Don’t quote me on that. The cost depends on several factors, such as those I’ve listed below:

• Part price and availability
• Shop labor rate
• Engine size and complexity
• Other potential necessary jobs (e.g., flushing the coolant)

In almost every case, the gasket itself is $50 or less. Not too bad.

The majority of the cost comes from the labor time needed to install the said gasket. This will vary from car to car, but I’d allow a couple of hours, depending on your engine’s design.

You can see how the cost quickly starts to add up.

You might be tempted to change the gasket yourself at home. This is a riskier option that I wouldn’t recommend to the average person. That said, it’s much cheaper.

Can I Replace My Intake Manifold Gasket Myself?

I understand wanting to save money by fitting this yourself. After all, the part itself is usually pretty cheap.

If you have some mechanical know-how, you can probably change your own intake manifold gasket. However, if you didn’t know what one was before reading this page, I advise against it.

Another (cheaper) option would be to consult a handy friend or family member.

Also, remember that V-engines have more complex intake manifolds. (Well, they have more complex everything, actually.) Misplacing the gasket on these (or any motor) might mean the fault continues or even worsens.

Each manufacturer designs its intake manifold gaskets differently. For example, some simply push into place. On others, you’ll need to line them up, replace the manifold, and then put a bolt through both simultaneously.

It’s also imperative to follow the instructions when torquing the bolts up. You must tighten them to the correct levels and in the described order.

If you don’t, the gasket will break straight away!

In general, then, while it is possible to change your own intake manifold gasket, go to a mechanic if you’re stuck.

Replacement Intake Manifold Gasket: Conclusion

When it comes to cars, I understand they can be expensive to run, and that can feel daunting. But you must pay attention to developing problems, no matter how insignificant they might feel.

Ignoring them always inevitably leads to more significant, more expensive faults down the road. This same principle applies to a leaking intake manifold gasket (as it does to everything!).