This driving me nuts trying to track it down. It comes and goes and is costing me big bucks at the gas pump.
I've replaced just FYI over the last year and a half for another problem, the knock sensor, plugs, amm, cap, rotor, wires, power stage, radio and fuel relay as well as the ECM, fpr, coolant sensor, plug for coolant sensor and O2 sensor.
Here is what it is doing occasionally it goes full rich and is a pain to drive smooth. I now have noticed that when it goes rich my boost gauge drops a few psi when it happens. Normally the gauge sits at 9:15-9:30 but when it goes rich the gauge jumps to 10:00 to 10:30. Usually I can push the throttle down and run it up to 5500 to 6k rpms in which it blows out lots of black smoke. Let off the throttle and the tach returns back to 9 - 9:30 normal area.
There is no rhyme or reason to why it is doing it. Because it comes and goes it never seems to want to do it when I'm at my mechanics or any where near his shop. I'm leaning to a going south newer coolant sensor or O2 sensor.
The only symptom that is noticeable is the increasing and decreasing vacuum at idle. Other than that it starts and idles fine.
Thanks