Depending on the year, make and model of a vehicle, it may have a plastic, aluminium or cast-iron intake manifold. All manifolds use gaskets between the intake manifold and the head. In some cases, a vehicle has a two-part intake manifold -- upper and lower. In most of these cases, the lower intake is aluminium or cast-iron and the upper piece is plastic. When the manifold is two-part, it will have two gaskets, one between the lifter galley and the lower intake, and one between the lower intake and upper intake manifold.
- Skill level:
- Moderately Challenging
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Things you need
- Can of carburettor cleaner
- Shop rags
Note whether the vehicle has a rough idle. If all other components work properly and no other reason for the rough idle exists, the intake manifold gasket is suspect.
Start the engine. Listen for a vacuum leak. If none of the vacuum hoses leak, an faulty intake manifold gasket may be the cause. Spray carburettor cleaner around the gasket-mating surface of the intake manifold, both upper and lower, if you have a double manifold. If the noise stops, the manifold is cracked or warped, or the gasket is bad.
Look on the ground underneath the vehicle. If water puddles on the floor near the centre of the engine on either side, and all other hoses are in good condition, the intake manifold gasket may need replacing.
Wipe any dirt, oil, grease or water from the area of the intake manifold gasket. Depending on how bad the gasket is broken, you may see nothing during idle except some steam, but you should be able to see water leaking from the gasket area if the gasket has a bad tear.
Tips and warnings
- If you have a double intake manifold, you do not need to replace the lower intake gasket if the upper one is bad. Always check the gasket-mating surfaces to ensure that the intake hasn't warped or isn't cracked. If you put a new gasket onto a defective manifold, the gasket will quickly blow out.