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

ACEMASTER

MEMBER
1999 CHEVROLET ASTRO
4.3L
6 CYL
2WD
AUTOMATIC
210,000 MILES

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.

Thursday, March 24th, 2022 AT 12:23 PM

3 Replies

JACOBANDNICKOLAS

MECHANIC
110,176 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.

Image (Click to make bigger)