IAC counts going to Zero! Hanging idle!
 

This is on my personal turbo truck. It currently has a ebay 92mm tb and a holley high ram intake. I am having an issue where it struggles on cold start up (have to pedal it for a lil bit) , Idle hangs around 1000rpm (750 commanded) and IAC counts go to zero at hot idle.

I have played with everything in the tune tht I can think of. I also had this issue with a stock tbss intake and ptm 92mm tb. I swapped to the holley high ram setup thinking it would help fix a cracked intake etc. Didn't work. I have been fighting this for a few weeks.

I can close tb blade all the way and counts still stay at 0. Ive checked all vaccum sources, intake leaks, etc. I cant find anything.

I have been tuning a lil over 4yrs and this is the first time ive had an issue like this tht I couldn't figure out. if anyone has any ideas im all ears. thanks.

how are you checking for leaks? Have you smoked it?

Is the engine able to actually reach the “desired idle rpm”? I’ve found that if this is unattainable, the “idle desired” aka IAC counts will keep going down to try and reach it.

Air essentially controls the rpm range (+/- off of target) at idle, spark maintains the target. If the rpm setting is too low for that cam, it’s not going to reach the “range” using air because vacuum (airflow) is reduced at low rpm. Try bumping the rpm up by 15-25 at a time until the counts stabilize.

You can can play with spark a bit too, but with different setups the targets are all dependent on mods.

I think we’d all like our big ass nasty merican cams to idle at 550 but unfortunately physics has other plans...

You may need to epoxy aroun your TB to close the gap between blade and body.

Remove TB, shine a light behind it, see how much light gets through. If a lot, build up with epoxy or ditch the eBay TB for a NW

Yup....that's what i had to do. Worked fine afterwards.

Your sig cracks me up. its Running.... nevermind….

Sad but true

It actually hangs around 950rpm. Every now and thin when the iac counts are good it will idle at 750 with a nice lope. Sounds amazing around the idle. I can usually achieve this when coming to a stop at a light etc.

Thin counts go to zero and it seems like timing locks out and idle just hangs back up.

Ill try pulling the tb off and give it a look over. I feel like it is suspect at this point. Ill also try an idle around 950ish if tb checks out. Ill report back my findings. Thanks guys!

i have similar issues with my car it wont return to adaptive idle all the time

Some of this could possibly be caused by the throttle cracker to.

My throttle cracker is disabled. It really helped my truck from a hanging idle while still rolling or coming to a stop. It wouldnt return to a complete idle until i was fully stopped. Works alot better disabled!

I removed tb yesterday. I shinned a light behind it like stated above. There was a noticable gap on top and bottom. Blade wouldnt fully return to a complete shut on the stop.

I loosened the 2 screws holding the blade and let it recenter itself. It will shut completely closed now.

Only thing tht sucks is i have a hole drilled into the blade. Whats the best way to close it up? Epoxy?

I've used a quality thick aluminum tape to close them up before. Put it on both sides of the blade.

My tb seems to have the pcv port and the iac passage opeded up together on the front side. (As in tied together)

I jb welded the open air passage. Imma gonna try and drill it back out. I think this will allow alot more air for iac to work properly. Hopefully this cures my cold start issue! Thoughts?

Yeah you need a 3/8 port for the iac or it cannot seem to adjust enough.

Ok i reinstalled tb without doing any changes to the iac passages. My idle is finally what im commanding. Stays around 8-850rpm.

Only thing is the cold start still sucks ass. I still have to pedal it for a few seconds on cold and hot start.

May need to play with the throttle follower table for some throttle swings.


Also ive always just added like 50 cam counts for start up airflow. It doesnt seem to be enough. Does anyone have any ideas on chnages to add more startup airflow? I could live with the way it idles if it would start up on its own!

Other than tht, Straightening the throttle blade seemed to have helped alot!

how are your STIT?

as far as start up airflow, get your RAF lined out first. Then start adding more air.

Follower will not affect cold starts. Look at your iac park position. Increase it at the temperatures it does not like to start.

85 iac counts is a bit high for warm idle. I would try to work down to 30 counts at warm idle now that you got the primary issue fixed