Odd idle hang
Thread Starter
On The Tree
Joined: Aug 2013
Posts: 139
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Odd idle hang i have a ls1 sns 3 cam prc 225 heads ls6 intake. Had someone I know tune it. Car starts fine and revs fine idles drop right down. But take it out in a drive and get everythig hot and it starts idle hanging very bad once you get it hot and above 50-60 mph. Like around 2,000 to 3,000. It will continue this habit until you stop and shut the car off and restart it. Replaced iac and tps sensor. Cleaned iac ports. Retorque intake. New pcv valve. When driving When still kind of cold isles drop down to around 11-1500. Also throwing po507 code due to this. Also in idle and revving the maf is showing whatever grams it’s pulling. Then when idle hang happens it’s showing either the same or a bit more than whenever you match the rpms in neutral. So I THINK that means i can eliminate it not getting unmetered air correct?? Is this just a hacked up tune? Or what else can it be? Car didn’t do this before the tune. So what value should I look at? Does this sound like a throttle cracker issue? I’m about to have the guy just disable it. Another thing is after a flash the car acts fine for a while then it starts. Like the adaptive idle is messing with it too. But idk. I have no clue about tuning. If it you think it could be a sensor let me know. I’m to the point I’ll throw parts at it. Thing is making me rip my hair out and cut my arms up feeling for vac leaks under the cowl lol.
Thread Starter
On The Tree
Joined: Aug 2013
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did this with brake clean. I can not for the life of me find a vac leak anywhere. Also if it was a vac leak why only when hot and restarting once or twice or letting it sit a few minutes then starting fixes the issue? I can pinch off booster hose and it doesn’t change. Plus all the air and emissions are gone. Only vac lines are pcv and hvac vac line. Manifold has all new gaskets. Torqued to 100 inch pounds now. I did swap my foam bottoms over from my ls1 and glued it with rtv. But a vac leak would be there all the time wouldn’t it? The y was a bit gummy on the pcv setup but I plugged all the ends and blew air into it and it held pressure. The cam is bigger than an ms3 and it does shake the motor a bit. Maybe I can try zip tying the map down into the manifold but that’s just a shot in the dark
TECH Fanatic
Joined: Dec 2017
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From: Bossier City, Louisiana
You might not realize this but the Brake Kleen stuff in the red can is not flammable - it does not burn. This is clearly stated on the front of the can. Thus, it is a poor choice for running vacuum leak checks. The same product in the green Brake Kleen can is highly flammable.
Rick
Rick
Thread Starter
On The Tree
Joined: Aug 2013
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Oh my. I have some kind of car quest brand I used. I guess I better make sure it’s flammable. Also have some of the throttle body/carb cleaner now. However if it was a vac leak why only when hot and why does restarting usually fix the issue?? The only questionable spot I had was the Y on the pcv lines in the back was kind of gummy feeling. Also I tossed the idea of the heads heating up and making the intake gaskets not seal but idk they are torqued down a bit more than specs. I shall try again with the car cold to see if I can find it and then again with car hot.
Launching!
Joined: Jan 2018
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Oh my. I have some kind of car quest brand I used. I guess I better make sure it’s flammable. Also have some of the throttle body/carb cleaner now. However if it was a vac leak why only when hot and why does restarting usually fix the issue?? The only questionable spot I had was the Y on the pcv lines in the back was kind of gummy feeling. Also I tossed the idea of the heads heating up and making the intake gaskets not seal but idk they are torqued down a bit more than specs. I shall try again with the car cold to see if I can find it and then again with car hot.
throttle cracker, throttle follower and rolling idle airflow tables
base running airflow
base running airflow ECT multiplier
are all areas to look at.
rev hang is from too much air past the TB blade either through the IAC (which you can edit) or mechanically past the blade or through an air bleed in the blade. you need to find the happy medium of allowing enough air past for stable cold idle and stable return to idle in a dynamic operation, but not so much that the RPM hangs on coast.
personally I disable rolling idle and just use cracker, follower and adaptive idle strategies. most times I drill and air bleed in the blade. I set the throttle stop and relearn the 0% TPS point at the spot where I can maintain target idle RPM at operating temperature with 13.8-14.7AFR with only 8 degrees timing. that tells me that it will be very stable for warm idle and can add air with the IAC and timing with ECT corrections to return a stable cold idle.
I use that method and then tune cracker and follower tables in conjunction with adaptive idle to get the coast RPM, idle RPM and return to idle RPM transition to where im reasonably happy. then to fine tune it I use the idle spark table to add or subtract timing in the correlating RPM columns in the vacuum area (0.08-0.20g/cyl). if you have RPM hang on coast from 2000rpm back to idle. changing idle spark values from 25-30 degrees back to 10 degrees in the 0.08-0.20 area from 2000rpm to 1200rpm makes it return to idle RPM target quick smart. idle spark is your friend for fine tuning DBC large cam cars
see attached example for rough guide. its from a long time ago.
manual LS1 intake exhaust 232/234 .598/.598 112 cam. 3.46 diff gears
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Thread Starter
On The Tree
Joined: Aug 2013
Posts: 139
Likes: 3
provided your TPS is 0% at idle (DBC) and 100% at WOT and doesn't get stuck reading 1 or 2% on return to idle then...
throttle cracker, throttle follower and rolling idle airflow tables
base running airflow
base running airflow ECT multiplier
are all areas to look at.
rev hang is from too much air past the TB blade either through the IAC (which you can edit) or mechanically past the blade or through an air bleed in the blade. you need to find the happy medium of allowing enough air past for stable cold idle and stable return to idle in a dynamic operation, but not so much that the RPM hangs on coast.
personally I disable rolling idle and just use cracker, follower and adaptive idle strategies. most times I drill and air bleed in the blade. I set the throttle stop and relearn the 0% TPS point at the spot where I can maintain target idle RPM at operating temperature with 13.8-14.7AFR with only 8 degrees timing. that tells me that it will be very stable for warm idle and can add air with the IAC and timing with ECT corrections to return a stable cold idle.
I use that method and then tune cracker and follower tables in conjunction with adaptive idle to get the coast RPM, idle RPM and return to idle RPM transition to where im reasonably happy. then to fine tune it I use the idle spark table to add or subtract timing in the correlating RPM columns in the vacuum area (0.08-0.20g/cyl). if you have RPM hang on coast from 2000rpm back to idle. changing idle spark values from 25-30 degrees back to 10 degrees in the 0.08-0.20 area from 2000rpm to 1200rpm makes it return to idle RPM target quick smart. idle spark is your friend for fine tuning DBC large cam cars
see attached example for rough guide. its from a long time ago.
manual LS1 intake exhaust 232/234 .598/.598 112 cam. 3.46 diff gears
throttle cracker, throttle follower and rolling idle airflow tables
base running airflow
base running airflow ECT multiplier
are all areas to look at.
rev hang is from too much air past the TB blade either through the IAC (which you can edit) or mechanically past the blade or through an air bleed in the blade. you need to find the happy medium of allowing enough air past for stable cold idle and stable return to idle in a dynamic operation, but not so much that the RPM hangs on coast.
personally I disable rolling idle and just use cracker, follower and adaptive idle strategies. most times I drill and air bleed in the blade. I set the throttle stop and relearn the 0% TPS point at the spot where I can maintain target idle RPM at operating temperature with 13.8-14.7AFR with only 8 degrees timing. that tells me that it will be very stable for warm idle and can add air with the IAC and timing with ECT corrections to return a stable cold idle.
I use that method and then tune cracker and follower tables in conjunction with adaptive idle to get the coast RPM, idle RPM and return to idle RPM transition to where im reasonably happy. then to fine tune it I use the idle spark table to add or subtract timing in the correlating RPM columns in the vacuum area (0.08-0.20g/cyl). if you have RPM hang on coast from 2000rpm back to idle. changing idle spark values from 25-30 degrees back to 10 degrees in the 0.08-0.20 area from 2000rpm to 1200rpm makes it return to idle RPM target quick smart. idle spark is your friend for fine tuning DBC large cam cars
see attached example for rough guide. its from a long time ago.
manual LS1 intake exhaust 232/234 .598/.598 112 cam. 3.46 diff gears
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I’m about to get the mvpi 2 from hptuners. It’s odd as in it can warm up and idle all day and rev and come right back down but once you drive it it gets stuck in a hang. Just for peace of mind I have an entire new pcv system and new map sensor and throttle body gasket in the mail. After that I know short of intake leak it’s pretty much tuning issue. I appreciate the in depth help. I tinkered with my lt1 tuning but never with hptuners or obd 2 stuff. I’m going to get my iac counts into range of about 60 and then just disable the throttle cracker first though. If that doesn’t work then I’ll just find a 2000 stock ls1 tune file and start from scratch. Having a lighter flywheel doesn’t help me much either I’m sure
Launching!
Joined: Jan 2018
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it will behave as you say at idle when its cold because the engine needs more air to idle. it needs less air to do the same at operating temperature.
it has too much air for warm idle hence you have a rev hang. that same volume is correct for when its cold, hence its behaviour being correct.
your IAC is the only dynamic control over airflow at idle TPS. it only has a set mechanical range. if its completely shut it cant reduce any more air volume.
start from scratch with stock file is best to avoid tables you don't know are edited confusing you.
don't forget to consider timing values too as they can influence idle also. more timing increases coastdown/idle rpm less decreases.
if rev hang on coast down shows 30 degrees. changing that to 6 degrees will stop it.
I prefer cracker mode over rolling idle. I disable rolling idle and use cracker, follower and adaptive idle only.
it has too much air for warm idle hence you have a rev hang. that same volume is correct for when its cold, hence its behaviour being correct.
your IAC is the only dynamic control over airflow at idle TPS. it only has a set mechanical range. if its completely shut it cant reduce any more air volume.
start from scratch with stock file is best to avoid tables you don't know are edited confusing you.
don't forget to consider timing values too as they can influence idle also. more timing increases coastdown/idle rpm less decreases.
if rev hang on coast down shows 30 degrees. changing that to 6 degrees will stop it.
I prefer cracker mode over rolling idle. I disable rolling idle and use cracker, follower and adaptive idle only.
Thread Starter
On The Tree
Joined: Aug 2013
Posts: 139
Likes: 3
Sorry for no update. Nothing has changed or been done. Hptuners is on backorder right now. But it is ordered
However to the previous post the car will idle when hot. You can rev it all day but as soon as you take it out for a drive it will then start hanging. I think I’m going to try and disable all of the cracker tables and rolling etc and then if it doesn’t effect the problem at all then I think I’m getting into an issue of too much timing on coastdown? Is there a table for that? Coastdown timing??
However to the previous post the car will idle when hot. You can rev it all day but as soon as you take it out for a drive it will then start hanging. I think I’m going to try and disable all of the cracker tables and rolling etc and then if it doesn’t effect the problem at all then I think I’m getting into an issue of too much timing on coastdown? Is there a table for that? Coastdown timing??
Launching!
Joined: Jan 2018
Posts: 283
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Sorry for no update. Nothing has changed or been done. Hptuners is on backorder right now. But it is ordered
However to the previous post the car will idle when hot. You can rev it all day but as soon as you take it out for a drive it will then start hanging. I think I’m going to try and disable all of the cracker tables and rolling etc and then if it doesn’t effect the problem at all then I think I’m getting into an issue of too much timing on coastdown? Is there a table for that? Coastdown timing??
However to the previous post the car will idle when hot. You can rev it all day but as soon as you take it out for a drive it will then start hanging. I think I’m going to try and disable all of the cracker tables and rolling etc and then if it doesn’t effect the problem at all then I think I’m getting into an issue of too much timing on coastdown? Is there a table for that? Coastdown timing??
also use the follower decay and delay tables to tune for your fault,
as far as spark goes you'll need to look at the tps and speed settings to enable or disable the main spark tables.
there is no coastdown spark table but coast down will be in the low air mass sections like 0.08-0.20g. edit either the main or idle tables in this area to help.
Thread Starter
On The Tree
Joined: Aug 2013
Posts: 139
Likes: 3
Alright hptuners finally shipped out. Should be here Tuesday. Gonna try and just mess with the follower and cracker values and also check my iac counts. I might snoop around in the hp repository for a similar tune and compare it
Thread Starter
On The Tree
Joined: Aug 2013
Posts: 139
Likes: 3
Just an update. For piece of mind I replaced entire pcv system and rtvd my map. I got my hptuners and set the idle a little lower to 850 rather than 920 it was set at. I flipped my throttle body screw and got my iac to about 110 hot. Then I disabled my throttle cracker. Everything is good. Car returns to idle. Except sometime it will fall on the idle return. I think I may have to add the throttle cracker back and just zero out the entire table except at a few rpm before idle. Does this sound right? Also should I tinker with the follower? I’d like the Rpms to drop a bit more quickly and give me a bit more engine braking if possible