Manufacture alarm on 99 astro van will not let van stay running

remove the inside trim panels on the left hand side. Most "snap" into place, but look for screws first before pulling on the panel edges.

that could be a timing issue as the vacuum helps with the timing /spark etc

is there a check engine light on? There are numbers of things that can cause this.

i have a 99 astro awd auto 4.3 what is the number of clutches it should have inthe transfer case6

have 99 astro same problem changed ignition coil runs fine.

NOX is created when the internal combustion temperature gets to high.The egr system uses burnt exhaust gases to line to cylinder walls.The purpose of this is decrease internal combustion temperature therefore reducing the amount of NOX created.Would look to a possible egr malfunction usually they will trigger the check engine light but not always.The 4.3L has been known to have issues with carbon buil up in the egr and the egr pintle not open and closing properly.

does the van have a factory alarm. if it does try locking the door with key and then unlocking it. that worked on my grand national.

dont not cut any wire find a alarm technician and ask them disable for you unit is link to vEhicle ECM DONT CUT AND FOR THE SAKE OF CUTTING MAKE SURE THIS DONT BY SOMEONE WITH KNOWLEDGE

try checking the park,neutral position switch