My '99 Astro runs great in town, however at highway speeds (high R.P.M. light throttle) the van bucks harshly. This problem is eliminated with heavy or no throttle. This improves somewhat with more time on the highway but doesnt go away. It can be produced in 3rd gear at lower speeds. It has a 3.73 rear axle, 90,000 miles and new plugs, cap, wires, filters etc. I even paid a mechanic to replace the fuel injectors. The mechanic said the computer showed no problems/codes. Thought injectors were it. Any input will help. Thanks

 

I am not a mechanic but I spent alot of money at a Chevy dealer with a problem that started like the one you describe. After a full tune up, new fuel pump, new computer, another fuel pump, and I think 4 tows I changed the distibutor cap myself and have not had a problem since. I

 

Thanks for the tip! Two weeks ago I ran the engine with the engine cover off in the garage. I slowly brought the RPM up and heard a "PECK-PECK-PECK" coming from the distributor cap. This was in time with the engine miss so I replaced all the tune up parts that were purchased at a discount parts chain with ones from an original equipment parts supplier. No problems since! I can`t say if it was the wires or the cap for sure, but I will stick with O.E. parts from now on.

 

have your machanic check for valve seat issues in the heads