Running rich 12afr

[1989toyotasupraandpickup]

Hello all and hope someone can help me. I own a 1989 toyota supra turbo and the car is idling very rich. its weird because when im cruising the a/f ratio goes to 17+ until i press the throttle down. while boosting the a/f ratio goes to 10-11.2. occasionally the a/f ratio at idle will go to 17 and stay there. When the car is cold the a/f ratio is 14.7 and when it warms up the a/f ratio will drop down to the low 12s. here is a link to show you what is going on http://www.youtube.com/watch?v=3pYrfDnYew4 . could a intake manifold gasket leak cause the car to run rich and lean while cruising? Bad Egr cause lean condition while cruising? its driving me nuts... dont want to drive it like this because i know something is wrong and not right. Timing is set to 10* jumpered. goes to 12* unjumpered. What is the problem.