where is the diagnostic port for this van? on 1993 Chevrolet G Series Van (G30)

The van "bucks" at freeway speed only when maintaining speed- stops if I give it any gas or back off the pedal. I'm thinking a vacummn leak. Has throttle body injection.

by in Sherwood, OR on April 09, 2010
2 answers
ANSWER by on April 11, 2010
it is under the left hand side of the dash. Don't rule out worn Spark Plug wires, very common for bucking jerking ( misfires) Lots of heat under that 'dog house' that covers up the motor. here is a link to repair info for your car http://bit.ly/mitchell_repair_manuals_online
ANSWER by on July 02, 2013
My van was doing this whenever I was coasting. It felt like I was pulling a trailer on a ruff road. I replaced the O2 sensor and it quit...I gave up on trying to remove what looked like original equipment and replaced the Y and O2 both...about 175 bucks for both, but it was worth it.