Chevy & GMC Vans

Hello guys, it's been so long since I've visited; that's a good sign the 'ol Astro is running great. I'm now at 191k.

My problem as of late is the stuttering, bucking, etc when it's cold. I leave the neighborhood early in the morning and it's fine, but once on the freeway, until it warms, it starts to buck. I'll put the cruise control on and leave it. After a bit of bucking, it works it's way out of the system and it continues to run fine the entire rest of the day.

My guess is a sensor …ideas?

Check & be sure that the heated air intake duct (That crinkly cardboard vacuum cleaner looking hose thingy) from the exhaust manifold to the air intake isn't crushed, missing, disintegrated etc. Air filter would be next followed by fuel filter. Poke around a bit...surprising what you can see that WON'T throw a code. THEN run the codes, if any. Gotta start somewhere. right?

WHOOPS...just saw you have a K&N; are you running a cold air intake?

thanks for your response. K&N, but not a cold air intake, all stock ducting.

Cleaned your mass air flow sensor lately?

I changed the intake manifold gasket and replaced the spider injectors. At that time, I also cleaned the Mass Air Flow. That was about 30k ago. Due for another?

No harm doing a mass air flow sensor cleaning & it is simple to do & costs nothing. Since you are asking for ideas, another suggestion is a slightly restricted fuel filter or fuel pressure dropping to the threshold of meeting the minimum required amount. A cold (not warm) engine requires more fuel to operate. If the fuel pressure or flow amount is low, this could result in your issue.

a few ideas i hadn't considered. fuel pumps never last on Astro's so you may be on to something.

UPDATE: It turns out it was low on trans fluid

So many miles later, the problem returned and became worse. It bucks when idling along, such as when on cruise control on freeway. Basically, it's noticeable when no or little fuel is being supplied. With this determination, I finally figured it out and 100% fixed it. The distributor was worn and needed replaced. $100 and an hour of labor and it is back to perfect. This was a long term troubleshoot experience. We're now at 221,000.

Great work!

Bucking at "part throttle" while cruising, (especially when you have over 150K miles) is typically a worn distributor. It happened to me. Sorry I didn't see this post in 2014, to post my reply! Glad you found the problem!