LT1 Random Warm Idle Stalling + Hard Restart
Thread Starter
Teching In
Joined: Aug 2025
Posts: 3
Likes: 0
LT1 Random Warm Idle Stalling + Hard Restart Hello everyone.
I have a 1994 Z28 Camaro LT1 automatic. I’ve owned it for about nine months and have been slowly renewing it while fixing small issues. Up until now there was always something to chase, but for the first time I’m totally stumped.
The issue:
The car randomly stalls at idle, but only once it’s warmed up. After it stalls, it usually won’t restart unless I wait a few minutes. If I try to start it immediately, it will only fire if I crank for 5–7 seconds; when it does start this way, it revs up to ~2000 rpm and then drops slowly. At that moment I get SES with DTC 36, and the car goes into limp/safe mode.
Key point:
Once it starts in this limp-mode state, it will NOT stall again, idling or driving. It will keep running indefinitely until I shut it off. When I shut it off and restart normally, the SES clears and the random stalling returns.
I connected Scan9495 today and recorded several logs. I’ll attach five files below.
Note: any file I save and try to reopen gives me an “index error.” If you get the same error, let me know so I can upload videos of the logs instead.
In the first file, you’ll see DTCs 18, 36, and 48.
• 18 is from earlier when I was isolating the injectors and i never cleared it before logging.
• 48 is from unplugging the MAF during testing, so false code here as well.
• 36 is the only real/active code. I’ve had it for 2 months, even before this stalling issue. As far as I know, DTC 36 shouldn’t stall the engine, and the problem existed before this behavior started. Also the opti is barely 5 month old.
Repairs done:
• Full ignition renewal a few months ago: new Opti, plugs, wires, coil, ICM.
• Fuel system: new fuel pump, fuel filter, and cleaned all 8 injectors with carb cleaner. I also replaced both O2 sensors at this point.
• Fuel pressure: 35 psi at idle, 42 psi prime/FPR unplugged.
• Mods from previous owner worth mentioning: long tube headers, Magnaflow exhaust, EGR delete, AIR pump delete, K&N filter.
Log explanations:
File 1:
Normal start. It stalls around position 810. Attempted restart at ~890; surprisingly it started. I gave it a slight throttle input as a reflex when it was about to die, and it recovered.
File 2:
I was testing actuators and manually set idle to 1200 rpm just to experiment. It unexpectedly stalled at position 1415. Multiple short crank attempts followed.
File 3:
Car was stalled; attempted two starts with no success.
File 4:
Normal start, then it dies after a few seconds.
File 5:
This is the long-crank scenario. I crank for several seconds, it fires, revs high on its own, then slowly comes down. It throws DTC 36 immediately after (I had reset it beforehand) and enters safe / limp mode.
After that, the car idles perfectly. Only the beginning of the file is interesting, the rest is just it idling. After i stopped the recording I decided to see how long it holds and was doing other work. Was pulling injector wires, checked for vacuum leaks, took phone calls etc. No stalling whatsoever in this safe mode condition. After 40–50 minutes I decided that was enough and shut it down...
This is the part that confuses me. I initially suspected a sticking injector bleeding off pressure and requiring a long crank to clear a flooded cylinder. But that doesn’t explain why it never happens in limp mode.
Any help is highly appreciated!
I have a 1994 Z28 Camaro LT1 automatic. I’ve owned it for about nine months and have been slowly renewing it while fixing small issues. Up until now there was always something to chase, but for the first time I’m totally stumped.
The issue:
The car randomly stalls at idle, but only once it’s warmed up. After it stalls, it usually won’t restart unless I wait a few minutes. If I try to start it immediately, it will only fire if I crank for 5–7 seconds; when it does start this way, it revs up to ~2000 rpm and then drops slowly. At that moment I get SES with DTC 36, and the car goes into limp/safe mode.
Key point:
Once it starts in this limp-mode state, it will NOT stall again, idling or driving. It will keep running indefinitely until I shut it off. When I shut it off and restart normally, the SES clears and the random stalling returns.
I connected Scan9495 today and recorded several logs. I’ll attach five files below.
Note: any file I save and try to reopen gives me an “index error.” If you get the same error, let me know so I can upload videos of the logs instead.
In the first file, you’ll see DTCs 18, 36, and 48.
• 18 is from earlier when I was isolating the injectors and i never cleared it before logging.
• 48 is from unplugging the MAF during testing, so false code here as well.
• 36 is the only real/active code. I’ve had it for 2 months, even before this stalling issue. As far as I know, DTC 36 shouldn’t stall the engine, and the problem existed before this behavior started. Also the opti is barely 5 month old.
Repairs done:
• Full ignition renewal a few months ago: new Opti, plugs, wires, coil, ICM.
• Fuel system: new fuel pump, fuel filter, and cleaned all 8 injectors with carb cleaner. I also replaced both O2 sensors at this point.
• Fuel pressure: 35 psi at idle, 42 psi prime/FPR unplugged.
• Mods from previous owner worth mentioning: long tube headers, Magnaflow exhaust, EGR delete, AIR pump delete, K&N filter.
Log explanations:
File 1:
Normal start. It stalls around position 810. Attempted restart at ~890; surprisingly it started. I gave it a slight throttle input as a reflex when it was about to die, and it recovered.
File 2:
I was testing actuators and manually set idle to 1200 rpm just to experiment. It unexpectedly stalled at position 1415. Multiple short crank attempts followed.
File 3:
Car was stalled; attempted two starts with no success.
File 4:
Normal start, then it dies after a few seconds.
File 5:
This is the long-crank scenario. I crank for several seconds, it fires, revs high on its own, then slowly comes down. It throws DTC 36 immediately after (I had reset it beforehand) and enters safe / limp mode.
After that, the car idles perfectly. Only the beginning of the file is interesting, the rest is just it idling. After i stopped the recording I decided to see how long it holds and was doing other work. Was pulling injector wires, checked for vacuum leaks, took phone calls etc. No stalling whatsoever in this safe mode condition. After 40–50 minutes I decided that was enough and shut it down...
This is the part that confuses me. I initially suspected a sticking injector bleeding off pressure and requiring a long crank to clear a flooded cylinder. But that doesn’t explain why it never happens in limp mode.
Any help is highly appreciated!
Thread Starter
Teching In
Joined: Aug 2025
Posts: 3
Likes: 0
Did some more testing today. I noticed my IAC count is very low when warmed up and could go down below 10, sometimes stabilizes at 6 and other times it can go down all the way to 0. However in limp mode the IAC is at 40-50.
I suspected 2 things, sticky/dirty IAC and or vacuum leak. I tried getting to the IAC without removing the TB but its just impossible. I dont have a gasket set for the TB so im trying to avoid removing it. However i sprayed some carb cleaner into the IAC inlet while cycling it through my laptop ( you can increase/decrease rpm using the IAC). No improvement.
Next was looking for vacuum leak. visually there was nothing abnormal anywhere. I then sprayed carb cleaner around all vacuum inlets but no effect at all. Next was "choking" the air inlet and I was thinking that if the engine doesnt stall then it might be pulling air from somewhere else. I remember from my previous BMW where simply placing my hand close to the intake it would stall, here however it behaved differently. I covered the TB with my hand almost completely, there was strong suction and the rpm fluctuated but the engine stayed running....
Next I then used a towel to completely block the IAC inlet, but the engine still wouldnt stall. It almost sounded like it was breathing through the towel.
Ooookay this was weird, I had an idea. I put back the intake elbow (rubber one) and then placed a metal can/bucket of nearly perfect size over the other end. The suction was so strong that the rubber elbow collapsed as the engine was starved for air, yet it continued running. Is this normal? At that point it was likely pulling air from small gaps around the throttle body and the bucket I could hear noise of small air ways. At this point I tried removing the bucket but the vacuum was so strong i could not do it without ripping the whole intake elbow. I had to manually shut the car to get it out. Is it supposed to be this stubborn? Hell I would be happy if it was this reluctant to die while im idling at a red light...
Also im thinking, could vacuum leak / faulty IAC cause the problem im describing?
My brain is getting all mushy from the overthinking. Why does it start normally at first. Then after 5-10 minutes it dies. No restart unless cranked for prolonged time and it enters limp mode. At that point it runs fine forever. Or until next restart in which itll be out of limp mode.
Also to add: the intake suction test was done in limp mode where the IAC count was at minimum 40. When the intake was blocked the IAC count went up steadily to >100.
I suspected 2 things, sticky/dirty IAC and or vacuum leak. I tried getting to the IAC without removing the TB but its just impossible. I dont have a gasket set for the TB so im trying to avoid removing it. However i sprayed some carb cleaner into the IAC inlet while cycling it through my laptop ( you can increase/decrease rpm using the IAC). No improvement.
Next was looking for vacuum leak. visually there was nothing abnormal anywhere. I then sprayed carb cleaner around all vacuum inlets but no effect at all. Next was "choking" the air inlet and I was thinking that if the engine doesnt stall then it might be pulling air from somewhere else. I remember from my previous BMW where simply placing my hand close to the intake it would stall, here however it behaved differently. I covered the TB with my hand almost completely, there was strong suction and the rpm fluctuated but the engine stayed running....
Next I then used a towel to completely block the IAC inlet, but the engine still wouldnt stall. It almost sounded like it was breathing through the towel.
Ooookay this was weird, I had an idea. I put back the intake elbow (rubber one) and then placed a metal can/bucket of nearly perfect size over the other end. The suction was so strong that the rubber elbow collapsed as the engine was starved for air, yet it continued running. Is this normal? At that point it was likely pulling air from small gaps around the throttle body and the bucket I could hear noise of small air ways. At this point I tried removing the bucket but the vacuum was so strong i could not do it without ripping the whole intake elbow. I had to manually shut the car to get it out. Is it supposed to be this stubborn? Hell I would be happy if it was this reluctant to die while im idling at a red light...
Also im thinking, could vacuum leak / faulty IAC cause the problem im describing?
My brain is getting all mushy from the overthinking. Why does it start normally at first. Then after 5-10 minutes it dies. No restart unless cranked for prolonged time and it enters limp mode. At that point it runs fine forever. Or until next restart in which itll be out of limp mode.
Also to add: the intake suction test was done in limp mode where the IAC count was at minimum 40. When the intake was blocked the IAC count went up steadily to >100.
On The Tree
Joined: Mar 2006
Posts: 122
Likes: 10
By the time I read all that, I forgot what I read. But it seems like this engiine doesn't stall when you choke the intake. So it probably has an intake leak somewhere - either external or internal. So its possible that, if you can't find it by spraying around the engine, the air is coming from the crank case.. When these cars were new, there was a rash of intake bolts being loose and causing problems like that. So maybe you got a simple problem, just hard to find.
Intake gaskets would be my guess or something with the egr, if you still have that crap.I got rid of it so long ago I can't remember how it works but I remember its a problem if it gets all corboned up and sticlks open.
Intake gaskets would be my guess or something with the egr, if you still have that crap.I got rid of it so long ago I can't remember how it works but I remember its a problem if it gets all corboned up and sticlks open.
Last edited by Kevin Blown 95 TA; Dec 16, 2025 at 03:21 PM.
Teching In
Joined: Feb 2010
Posts: 2
Likes: 0
Hello everyone.
I have a 1994 Z28 Camaro LT1 automatic. I’ve owned it for about nine months and have been slowly renewing it while fixing small issues. Up until now there was always something to chase, but for the first time I’m totally stumped.
The issue:
The car randomly stalls at idle, but only once it’s warmed up. After it stalls, it usually won’t restart unless I wait a few minutes. If I try to start it immediately, it will only fire if I crank for 5–7 seconds; when it does start this way, it revs up to ~2000 rpm and then drops slowly. At that moment I get SES with DTC 36, and the car goes into limp/safe mode.
Key point:
Once it starts in this limp-mode state, it will NOT stall again, idling or driving. It will keep running indefinitely until I shut it off. When I shut it off and restart normally, the SES clears and the random stalling returns.
I connected Scan9495 today and recorded several logs. I’ll attach five files below.
Note: any file I save and try to reopen gives me an “index error.” If you get the same error, let me know so I can upload videos of the logs instead.
In the first file, you’ll see DTCs 18, 36, and 48.
• 18 is from earlier when I was isolating the injectors and i never cleared it before logging.
• 48 is from unplugging the MAF during testing, so false code here as well.
• 36 is the only real/active code. I’ve had it for 2 months, even before this stalling issue. As far as I know, DTC 36 shouldn’t stall the engine, and the problem existed before this behavior started. Also the opti is barely 5 month old.
Repairs done:
• Full ignition renewal a few months ago: new Opti, plugs, wires, coil, ICM.
• Fuel system: new fuel pump, fuel filter, and cleaned all 8 injectors with carb cleaner. I also replaced both O2 sensors at this point.
• Fuel pressure: 35 psi at idle, 42 psi prime/FPR unplugged.
• Mods from previous owner worth mentioning: long tube headers, Magnaflow exhaust, EGR delete, AIR pump delete, K&N filter.
Log explanations:
File 1:
Normal start. It stalls around position 810. Attempted restart at ~890; surprisingly it started. I gave it a slight throttle input as a reflex when it was about to die, and it recovered.
File 2:
I was testing actuators and manually set idle to 1200 rpm just to experiment. It unexpectedly stalled at position 1415. Multiple short crank attempts followed.
File 3:
Car was stalled; attempted two starts with no success.
File 4:
Normal start, then it dies after a few seconds.
File 5:
This is the long-crank scenario. I crank for several seconds, it fires, revs high on its own, then slowly comes down. It throws DTC 36 immediately after (I had reset it beforehand) and enters safe / limp mode.
After that, the car idles perfectly. Only the beginning of the file is interesting, the rest is just it idling. After i stopped the recording I decided to see how long it holds and was doing other work. Was pulling injector wires, checked for vacuum leaks, took phone calls etc. No stalling whatsoever in this safe mode condition. After 40–50 minutes I decided that was enough and shut it down...
This is the part that confuses me. I initially suspected a sticking injector bleeding off pressure and requiring a long crank to clear a flooded cylinder. But that doesn’t explain why it never happens in limp mode.
Any help is highly appreciated!
I have a 1994 Z28 Camaro LT1 automatic. I’ve owned it for about nine months and have been slowly renewing it while fixing small issues. Up until now there was always something to chase, but for the first time I’m totally stumped.
The issue:
The car randomly stalls at idle, but only once it’s warmed up. After it stalls, it usually won’t restart unless I wait a few minutes. If I try to start it immediately, it will only fire if I crank for 5–7 seconds; when it does start this way, it revs up to ~2000 rpm and then drops slowly. At that moment I get SES with DTC 36, and the car goes into limp/safe mode.
Key point:
Once it starts in this limp-mode state, it will NOT stall again, idling or driving. It will keep running indefinitely until I shut it off. When I shut it off and restart normally, the SES clears and the random stalling returns.
I connected Scan9495 today and recorded several logs. I’ll attach five files below.
Note: any file I save and try to reopen gives me an “index error.” If you get the same error, let me know so I can upload videos of the logs instead.
In the first file, you’ll see DTCs 18, 36, and 48.
• 18 is from earlier when I was isolating the injectors and i never cleared it before logging.
• 48 is from unplugging the MAF during testing, so false code here as well.
• 36 is the only real/active code. I’ve had it for 2 months, even before this stalling issue. As far as I know, DTC 36 shouldn’t stall the engine, and the problem existed before this behavior started. Also the opti is barely 5 month old.
Repairs done:
• Full ignition renewal a few months ago: new Opti, plugs, wires, coil, ICM.
• Fuel system: new fuel pump, fuel filter, and cleaned all 8 injectors with carb cleaner. I also replaced both O2 sensors at this point.
• Fuel pressure: 35 psi at idle, 42 psi prime/FPR unplugged.
• Mods from previous owner worth mentioning: long tube headers, Magnaflow exhaust, EGR delete, AIR pump delete, K&N filter.
Log explanations:
File 1:
Normal start. It stalls around position 810. Attempted restart at ~890; surprisingly it started. I gave it a slight throttle input as a reflex when it was about to die, and it recovered.
File 2:
I was testing actuators and manually set idle to 1200 rpm just to experiment. It unexpectedly stalled at position 1415. Multiple short crank attempts followed.
File 3:
Car was stalled; attempted two starts with no success.
File 4:
Normal start, then it dies after a few seconds.
File 5:
This is the long-crank scenario. I crank for several seconds, it fires, revs high on its own, then slowly comes down. It throws DTC 36 immediately after (I had reset it beforehand) and enters safe / limp mode.
After that, the car idles perfectly. Only the beginning of the file is interesting, the rest is just it idling. After i stopped the recording I decided to see how long it holds and was doing other work. Was pulling injector wires, checked for vacuum leaks, took phone calls etc. No stalling whatsoever in this safe mode condition. After 40–50 minutes I decided that was enough and shut it down...
This is the part that confuses me. I initially suspected a sticking injector bleeding off pressure and requiring a long crank to clear a flooded cylinder. But that doesn’t explain why it never happens in limp mode.
Any help is highly appreciated!
Thread Starter
Teching In
Joined: Aug 2025
Posts: 3
Likes: 0
Sorry for the mushy writeup lol. Im a bit lost myself since I cant figure out if I have a problem or multiple problems that im discovering on the go. The stalls could be one and the vacuum leak might be a different.
Regarding the leak, Im trying to avoid opening up the engine by doing everything else first. The EGR is deleted.
@morbital YES it does! I assumed first it was smoking white because of the sudden cold weather ( I live in Scandinavia) and then I suspected it might be coolant leak. So Ive been keepin an eye on the coolant for the past 3 days and now its confirmed it is at exactly the same level. Thanks for the tip regarding the PCV valve, please update me how it goes for you.
Regarding the leak, Im trying to avoid opening up the engine by doing everything else first. The EGR is deleted.
@morbital YES it does! I assumed first it was smoking white because of the sudden cold weather ( I live in Scandinavia) and then I suspected it might be coolant leak. So Ive been keepin an eye on the coolant for the past 3 days and now its confirmed it is at exactly the same level. Thanks for the tip regarding the PCV valve, please update me how it goes for you.
Last edited by Vincent Sil; Dec 19, 2025 at 04:22 PM.