boschmann , thanks for your response , The 90 Jetta does not have a check egine light and the guys down at the VW dealer laughed at me when I asked for the VAG test , they said that a car that old (120,000 miles) shows everything being bad . What do you think , should I have them check it any how , I'm still thinking If I could find out what exactly the control unit does with the information it recieves from the CTS , What other functions that information influenes , we might be able to figure this thing out . If you have anything technical , lay it on me . Thanks