Shuddering of car on shifting into any drive position

[nawalsingh]

I have a 1996 Cadillac STS with a 4.6 DOHC motor. I bought this one with 120 K miles on it in August 2004 and added another 10 K miles. The car gives great gas mileage (25-27 MPG). Recently I noticed that the car shudders upon the shifting the gear into Drive, Rear or any other drive position. This shuddering is not noticeable when the motor is idling with the gear shift in Park position. The shuddering disappears when the car is in motion, it even touches 70-85 mph without trouble. Occassionaly the Service Engine Soon light flashes indication a misfire problem. The service engine soon light generally goes out on its own often. The OBD II codes that I managed to retrieve a couple of times indicated a misfire in cylinder number 7, EGR malfunction, PO717 (turbine speed sensor no signal). Strange the P0717 may come once in 2K miles and go away. Last week I got the transmission flushed along with a replacement of the transmission filter. There are no leaks around the transmission or motor inspite of the vehicles age and the miles on it. Can someone give me an opinion? Secondly can I changeover to synthetic oil given the car age and miles on it?

 

[Dave Brooks]

Besides the misfiring, you could have worn or damaged, trans or engine mounts or both. Had a Deville that would do that and turned out the top motor dumbells had very worn rubbers. Also check your drivers side lower trans mount as that can cause a similar shudder. The "shudder tells me that your engine/ trans is rocking very slightly bacl and forth. Check out and see if that is a possibility.
Dave

 

[Dave Brooks]

P.s. DO NOT go for the synthetic oil as you will see an hugh increase in oil consumption and vivible oil burning. Can't say why but I tried it and went back to conventional oil and lost the oil smoke immediately.
Dave