For 1990-2009 cars

1. Inspect the intake manifold (6) for damage.
2. Inspect the intake manifold for cracks near the mounting holes.
3. Inspect the crankcase ventilation passages for any blockage, and clean the passages if necessary.
4. Clean the intake manifold mating surfaces.
5. Use a straight edge and a feeler gauge, and measure the intake manifold mounting surface for warping.

Intake Manifold Maximum Warping
0.10 mm (0.0039 in)

6. If the warping is greater than the maximum, repair or replace the intake manifold.