Lurches at stop light, foot on brake and in drive idle goes rough

1999 CHEVROLET ASTRO
210,000 MILES • 4.3L • 6 CYL • 2WD • AUTOMATIC
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ACEMASTER
  • MEMBER
  • 2 POSTS
After driving for a bit when I come to a stoplight, I'm completely stopped, the van starts idling rough and feels like it's trying to lurch forward. When I put it in neutral the idle is still rough. When I start going again the drive's fine. It has begun to do this every time I stop and now not just long drives but drives in town. Never experienced this before so in need of some help and advice on what I should do and what it could be please.
Mar 24, 2022 at 5:23 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,240 POSTS
Hi,

The first thing to check for is an engine vacuum leak. A leak can cause a rough idle and even stalling. Here is a link showing how to do this:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If no leaks are found, you may want to consider servicing the idle air control valve (IAC). The IAC is responsible for maintaining idle speed under different conditions. There are times they are partially plugged, restricting air, or the IAC can fail.

The IAC is located on the throttle body. If you remove the air intake tube, it is positioned right below it. See pic 1 below.

Here is a link that explains how to service one:

https://www.2carpros.com/articles/idle-air-control-valve-service

Let me know what you find or if you have other questions.

Take care,

Joe

See pic below. Also, I highlighted the IAC and have an arrow pointing to where it mounts. Make sure that area is clear of any dirt or carbon that can restrict airflow.
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Mar 24, 2022 at 1:22 PM
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ACEMASTER
  • MEMBER
  • 2 POSTS
Thank you. I'll check both suggestions after and let you know what I find.
Mar 25, 2022 at 2:07 AM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,240 POSTS
Hi,

You are very welcome. Let me know what you find and what I can do to help.

Take care,

Joe
Mar 25, 2022 at 5:01 AM
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