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#1 |
![]() Join Date: Jan 2024
Location: Boston, MA
Posts: 167
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I've been chasing a situation where my engine stalls when cold rather easily, as well as when the engine is warm if coming to a quick stop.
According to TunerPro RT my IAC steps were ~60 at idle once the car is warm. This seems a bit higher than others here have suggested it should be. The first thing I did was remove my IAC and clean the pintle and bore. Before/after. Yes, the O-Ring was put back even though it isn't in the after shot. IMG_7703.jpg IMG_7687.jpg I then attempted to go through the procedure to set minimum idle air and reset the IAC here: https://zr1.net/forum/showthread.php?t=27764 All was going well, but in step 6 my throttle stop screw was basically already turned in (clockwise) as far as it can go, so my understanding is I have no adjustment left to "lower" the minimum idle air. It was a hex head screw, 8mm I believe. Have any of you had to get a longer screw? This was after messing around with it a bit trying to back it off. When I started the nut and screw head were both all the way in. IMG_7693.jpg Interestingly if I let the engine run the idle would start around 1200 (ECM's commanded desired idle was 850), then start climbing in small increments and slowly run away. In other words, it would start at 1200, then 1250, then 1300, etc. and keep climbing until I killed the engine. Vacuum leak? I don't understand how with the IAC unplugged and the throttle body blades not moving the engine was able to gain so much RPM. The TPS was at 0.53v the whole time. Wondering if I should smoke the intake and look for leaks. The car does idle dead nuts where the ECM wants it, but was hoping to get IAC counts down and improve this stalling situation. All ideas are welcome. ![]()
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1987: Z51 Coupe, Z51, 4+3, Yellow / Graphite 1994: ZR-1 #150, Admiral Blue / Black 2015: Z06 Coupe, Z07, M7, Arctic White / Red Last edited by scorp508; 07-03-2024 at 10:50 AM. |
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#2 |
![]() Join Date: Jul 2020
Location: Nashville TN
Posts: 314
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I am confused. You describe trouble keeping idle and high IAC counts followed by surging rpm that seems to be air leak related.
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#3 |
![]() Join Date: Jan 2024
Location: Boston, MA
Posts: 167
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Sorry I probably could have laid it out better.
Before doing anything. 1. Car holds ECM commanded idle speed great. IAC shows steadily around 60 steps at idle once warm. 2. When cold, car stalls when coming to a slow stop nearly 100% of the time. 3. When warm, car occasionally stalls only when coming to an unexpected hard stop. While trying to set min air via stop screw and IAC disconnected. 1. Can't get idle low enough via stop screw. Screw is already turned inward as much as it can physically go. 2. After about 20 seconds of engine running the idle begins creeping upwards with no end in sight until I kill the engine. Put it back together as I had to go pickup my son at daycare, and did the final IAC reset steps even though I wasn't happy with it yet. 1. Car holds commanded idle. 2. IAC steps now 80. My stop screw is not "as closed" as it was when I started, so this sort of makes sense. 3. No apparent runaway idle increase.
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1987: Z51 Coupe, Z51, 4+3, Yellow / Graphite 1994: ZR-1 #150, Admiral Blue / Black 2015: Z06 Coupe, Z07, M7, Arctic White / Red |
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#4 |
Join Date: May 2007
Location: Chicagoland, IL
Posts: 9,696
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Did u plug in ALDL, TURN IGNITION ON, then unplug IAC first? The. Unplug ALDL B4 turn off ignition? This closes off IAC port.
Also, throttle blade closes as u back out set screw. At 60 counts, most of the idle air is going thru the IAC.
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[SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX Last edited by XfireZ51; 07-03-2024 at 01:22 PM. |
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#5 | ||
![]() Join Date: Jan 2024
Location: Boston, MA
Posts: 167
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I could remove the IAC again and confirm the pintle is fully extended before moving to the next step, unless that runs some kind of risk. Quote:
I don't know if this matters, but at the point where I was going to adjust the stop screw with the engine running I did have TunerPro RT datalogging via the ALDL to get a better read on RPM than the dash itself. |
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#6 | |
Join Date: May 2007
Location: Chicagoland, IL
Posts: 9,696
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If u have IAC counts, that would indicate no leak especially w 60. The IAC is doing all the work of keeping the motor idling.
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[SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX |
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#7 | ||
![]() Join Date: Jan 2024
Location: Boston, MA
Posts: 167
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#8 |
![]() Join Date: Jan 2024
Location: Boston, MA
Posts: 167
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How far should a fully extended pintel be? I'm measuring 17.6mm from the tip to the black casing just before the o-ring. Closer to 27.5 if I measure tip to the flange that mates against the TB.
![]() ![]() This looks like close to 28mm to the flange is accurate. I just tried again and even with the screw fully backed off I can't get it below 1200 rpm when commanded to 850, but if I button it all up it idles nice and low. ![]()
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1987: Z51 Coupe, Z51, 4+3, Yellow / Graphite 1994: ZR-1 #150, Admiral Blue / Black 2015: Z06 Coupe, Z07, M7, Arctic White / Red |
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#9 |
Join Date: May 2007
Location: Chicagoland, IL
Posts: 9,696
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When u connect ALDL, turn ignition ON, how many steps are showing for the IAC using ur datalogger?
One other thing to try is take IAC OUT and plug IAC port to seal it. Make sure the IAC IS UNPLUGGED b4 trying to start motor.
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[SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX Last edited by XfireZ51; 07-03-2024 at 06:58 PM. |
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#10 |
![]() Join Date: Jul 2007
Location: Bartlett, IL
Posts: 7,153
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To confirm the IAC is all the way in. I loosen it so I see it move away from the TB, then tighten after I unplug it.
I was fighting IAC stuff last year. Mind posting your IAC table settings in the PROM?
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1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - Borla Catback Late Model IH - Plenum Coilovers - 4.10s Custom Interior NCM Lifetime Member #978 |
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