The intake shutter valve system may require checking of the vacuum it generates and adjustment of the diaphragm that operates the air shutter. To check, remove the plug in the intake manifold. Install an adapter with metric threads in place of the plug, and connect a vacuum gauge. Disconnect the electrical connector at the 3-way valve. Then, start the engine and run it at idle. Now, read the vacuum gauge. It should read approx. 16.92 in.Hg.
If the reading is not correct, adjust the adjusting screw on the shutter valve (located just to the right of the vacuum gauge on the air intake). Then, stop the engine, reconnect the electrical connector, and replace the plug in the intake manifold.