For the past 6 months I have had an idle surge when the car is warmed up. The idle would jump from 500 to 1000 or so randomly. So I got the car scanned by a buddy and the only thing that we noticed was that the IAC count would be at a constant of 3 and when the car would surge the IAC count would jump to 40, every time the motor surged this jump happened. The car is pretty stock with headers a cold air intake and exhaust. Already tired to replace IAC valve, it did not help

PLEASE HELP

thanks

Rob

 

IAC counts as low as 3 points to a vacuum leak


0 IAC counts is closed, so 3 is almost closed, 20-45 ish is normal, but in reallity, anywhere other then closed/almost closed(under 10?) or max open(not sure, its high though) is good

 

Thanks that is what I was thinking, does any one else have any ideas?

 

If your car is stock (you post no mods), IAC counts should be in the 20-40 range on a warm engine.
The IAC counts change based on what the computer tells it to do. So you have to determine what is causing the computer tell it to change.
IAC counts at 3 indicate the engine is getting some air from another source like Dave said.

 

Whoa. 3 is super low. But other folks already gave you info on that.

The idle surge might be the same issue as the low IAC count, or it might not. If you get the time just watch the RPM on the scanner and make sure there's not a momentary obviously incorrect rpm shown, especially if the tach twitches right before a surge.

 

I will check that, thanks for all your help guys

 

Okay, sorry, but I need to bring this post back from the dead. I'm having a similar surging problem, but my IAC count is closer to normal, anywhere from 15-30 at idle. The thing that bothers me is the quote above.... I AM getting a couple obviously incorrect RPM cells and the tach does twitch before the engine surges. What does that mean?

 

I'm having a similar problem. It started after I adjusted my throttle cable to get 100% WOT. The TB valves are are just slightly open when it stays around 1000rpm. If I push it with my finger it settles back to the correct rpm. I have not swapped the IAC yet. I still need to check the datalogs also. I will probably pull the TB and clean it. Any recommendations on where or what to grease it with? Where should I look for vacum leaks? Any typical spots where these occur?

Thanks

 

A sudden change in the RPM for a few frames on a scanner may be the result of a corrupt pulse pattern from the Opti. Check the Opti harness connectors for starters.

 

will do.... thanks injuneer

 

I just got a 1998 z28, the idle is erratic, it gets worst with the air condition on, if any one has good suggestions will be appreciated. Thanks

 

Scan it and watch how the system responds to the changes in idle. What happens with your A/C? Does the idle RPM simply drop, or does the RPM become more erratic?

Finally, you have a 98 Z28, and that's not an LT1. You need to post this question on the "LS1 Based Engine Tech" forum.