What causes idle to hang?

[sfc rick]

I'm curious to know why after fixing vacuum leaks, my car still hangs when coming to a stop, then idles fine when stopped. It also doesn't do this all the time, but only on some occasions. It can do this one time and when I start the car up the next time it runs perfect. Or it can hang just for a couple of times then goes back to perfect idling when I'm just driving down the road. It can run perfect then after I shut it down and start it back up, it's hanging until the next time I stop and kill the car.

Any suggestions? is it somehow still reading past vacuum issues? and I need to clear the history somehow?



It's a 98 C5 6 speed.

[99LS1SS]

What modifications do you have? Also, you need to post a tune.

[printmanjackson]

too much air

[sfc rick]

OK, still looking for vacuum leaks.............

[printmanjackson]

you might get more help if you post up your tune and then post up a couple of logs and the confg showing what's going on.

It makes it easier for others here to help

[RACINGVORTEC5.3]

I think you should try cleaning the TB with some carb cleaner Just remember to remove TPS and IAC I think that should do it.....
Sometimes when theres dirt in the IAC motor canal it isnt able to close all the way or it doesnt move fast enogh and maybe thats where the vacume leak maybe

[vette_c6]

as printmanjackson said ,, to much air ,, post your file ,,,
u might need to adjust ,, or if you have changed your TB or cleaned it ,,, you might need to LEARN it in the VCM scanner

[wyochimneysweep]

my hangs and its because my tps doesn't return to the same postition every time. some times it stops at 2% and other times its at 0%. Watch for this in the scanner. Not saying your having the same problem but i am. not sure if its the sensor or a weak spring.

[Britt2020]

If you have just recently made any drastic changes to the motor, like heads or cam and have determined that you in fact do not have a vacuum leak, you may try this.

It’s an excerpt from a repost by Foff667. Foff667 credited the origin of the post to a Nogo.

"If the idle holds at 2000 RPM for extended periods of time reduce the P/N Airflow Decay table for all points above 10 MPH by 5% (multiply by 95) until this stops. Be vary careful on this table."

Hope this helps.

[badazz81z28]

Any updates to this thread? All the responses make sense if it hangs all the time, but it comes and goes...What would cause that?