No IAC, sudden high idle

[WillExoIX]

Hey Guys been awhile.

Ms1 V3.0 29Yxx firmware (forgot the rest)
GM HEI ignition on a turbo 2.8 60*v6 motor
Running fuel and spark.

I know you are going to ask for a log, I have the tune to upload, but will have to grab a log once the car cools down to replicate the issue.

Here is the jist of it. I am not running an IAC; it is unplugged and fully extended to block the IAC passage. I have a beautiful idle of 750-800rpms, have made ALOT of progress with the tune, However, the moment I touch the throttle in any way shape or form, the idle jumps to 1400rpms! It does not come back down no matter what I do, unless the car is shut down and cools off completely. I do have to give a little throttle to keep it going when first cranking it, but the high idle does not present itself then, only when mostly warmed up. TPS registers 0% at the time of the high idle.

Any other info needed just ask, will have a log uploaded in a few hours.

TIA

[Peras]

Hey Guys been awhile.

Ms1 V3.0 29Yxx firmware (forgot the rest)
GM HEI ignition on a turbo 2.8 60*v6 motor
Running fuel and spark.

I know you are going to ask for a log, I have the tune to upload, but will have to grab a log once the car cools down to replicate the issue.

Here is the jist of it. I am not running an IAC; it is unplugged and fully extended to block the IAC passage. I have a beautiful idle of 750-800rpms, have made ALOT of progress with the tune, However, the moment I touch the throttle in any way shape or form, the idle jumps to 1400rpms! It does not come back down no matter what I do, unless the car is shut down and cools off completely. I do have to give a little throttle to keep it going when first cranking it, but the high idle does not present itself then, only when mostly warmed up. TPS registers 0% at the time of the high idle.

Any other info needed just ask, will have a log uploaded in a few hours.

TIA

My best guess is that the throttle plate does not close off the air completely after it's been warmed up and moved from it's initial position.
Take the intake hose off just before the throttle plate and blip it one time to get the high idle, than use the palm of your hand to close the intake - if the RPMs don't go down, you have an air leak somewhere on the intake manifold.

[WillExoIX]

Hey Guys been awhile.

Ms1 V3.0 29Yxx firmware (forgot the rest)
GM HEI ignition on a turbo 2.8 60*v6 motor
Running fuel and spark.

I know you are going to ask for a log, I have the tune to upload, but will have to grab a log once the car cools down to replicate the issue.

Here is the jist of it. I am not running an IAC; it is unplugged and fully extended to block the IAC passage. I have a beautiful idle of 750-800rpms, have made ALOT of progress with the tune, However, the moment I touch the throttle in any way shape or form, the idle jumps to 1400rpms! It does not come back down no matter what I do, unless the car is shut down and cools off completely. I do have to give a little throttle to keep it going when first cranking it, but the high idle does not present itself then, only when mostly warmed up. TPS registers 0% at the time of the high idle.

Any other info needed just ask, will have a log uploaded in a few hours.

TIA

My best guess is that the throttle plate does not close off the air completely after it's been warmed up and moved from it's initial position.
Take the intake hose off just before the throttle plate and blip it one time to get the high idle, than use the palm of your hand to close the intake - if the RPMs don't go down, you have an air leak somewhere on the intake manifold.

Its not that, otherwise it wouldn't idle at 800rpms in the beginning and the tps wouldn't be reading 0%. I have already checked the throttle plate; It's open just enough to give me the 800rpm idle.

EDIT-The idle starts at 650-700rpms cold and runs 800-850rpms warmed up. Soon as I hit the throttle and the rpms come back down it just sits at 1400ish rpms. This is a new thing as its never done it before in the 9 months after the MS and turbo install.

[Peras]

Its not that, otherwise it wouldn't idle at 800rpms in the beginning and the tps wouldn't be reading 0%. I have already checked the throttle plate; It's open just enough to give me the 800rpm idle.

EDIT-The idle starts at 650-700rpms cold and runs 800-850rpms warmed up. Soon as I hit the throttle and the rpms come back down it just sits at 1400ish rpms. This is a new thing as its never done it before in the 9 months after the MS and turbo install.

Did that started happening after you done some changes to your tune?
Anyway I would take off the intake hose and do the "hand palm" test to confirm is it an air leak problem - just to rule it out.
BTW I've seen cars getting high idle and boost leaks because of the throttle blade holder seals going bad.

[WillExoIX]

Its not that, otherwise it wouldn't idle at 800rpms in the beginning and the tps wouldn't be reading 0%. I have already checked the throttle plate; It's open just enough to give me the 800rpm idle.

EDIT-The idle starts at 650-700rpms cold and runs 800-850rpms warmed up. Soon as I hit the throttle and the rpms come back down it just sits at 1400ish rpms. This is a new thing as its never done it before in the 9 months after the MS and turbo install.

Did that started happening after you done some changes to your tune?
Anyway I would take off the intake hose and do the "hand palm" test to confirm is it an air leak problem - just to rule it out.
BTW I've seen cars getting high idle and boost leaks because of the throttle blade holder seals going bad.

I will give that a shot after I get off work tomorrow. at 300k miles it is a possibility. thankfully I have a whole other motor in my shed, lol.

[Michael]

Almost certainly manifold air leak in some shape or form. - Michael

[WillExoIX]

Almost certainly manifold air leak in some shape or form. - Michael

Thats what it seems like to me as well. I have a hose clamp on every hose, check valve on the PCV, I did recently take the intake manifold off to change the valve cover gaskets, but this issue was present before that.

All emissions equipment is removed, bare minimum for vacuum lines. Just the line to the HVAC panel, and the MAP line for the MS, which has a T off it for my mechanical boost gauge. All have spring clamps on them as well.

Tomorrow I will get a startup log (and hopefully get some pointers on a better startup), and let the car warm up and replicate the issue. Then I will check all connections in the charge piping and intake manifold and go from there.

Here is what is strange, I have to pump the throttle to keep the car going after cranking, (separate issue; no IAC. I have ASE turned off and am using only WUE instead), and the issue does not present itself then, once I can let off the throttle to keep it going, the idle is normal. Its once it warms up some that if I hit the pedal it won't come back down under 1400.

That right there makes me think its something besides a vacuum leak, but AFAIK nothing else would cause an issue like this. Its just weird.

Will post up the log tomorrow.

[WillExoIX]

Ok, here is the log and current tune. Towards the end, I pinched the MAP line twice and the idle started to drop.

Let me know if you guys can see anything.

Just after 843 seconds in the log is where it happens. Clear as day in the log.

Seconds 1134 and 1230 is where I pinch the MAP line.

[WillExoIX]

Here is another log, high idle pretty much right off the bat. I backed the throttle screw out to get the idle down, however I fear that when I try to start it cold, I am going to have to redo the idle screw to start it.

This makes absolutely no sense to me. How can it possibly be a vacuum leak if it doesn't present itself until warm, AND I rev it several times? Sprayed carb cleaner all around and NO change in the rpms AT ALL.

[Matt Cramer]

Any chance the throttle isn't returning to fully closed?

[WillExoIX]

Any chance the throttle isn't returning to fully closed?

TPS returns to the same position and percentage in tunerstudio.

I did back off the throttle screw to bring the idle down when the high idle presents itself, but that makes me have to hold the throttle open to start the car when cold.

Kind of defies explanation to me.

[WillExoIX]

More perplexing than anything is the fact that it completely went away on its own without making any changes.

[WillExoIX]

Can consider this one solved as well. Mechanical issue.

[IMG]//images.tapatalk-cdn.com/16/02/26 ... e88a08.jpg

BIG vacuum leak. The vacuum while the engine was running would pull it closed. The surging low load was cause the vacuum was rising and falling, causing that leak to open and close, causing huge AFR swings.

Its fixed now.

[slow_hemi6]

[WillExoIX]

Hmm, thats odd, thanks.

[slow_hemi6]

Just a typo mate. easy fix.