Not going in to "Decel Enlean"
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Joined: Mar 2009
Posts: 60
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From: Memphis TN
Not going in to "Decel Enlean"
My car (stock '87) is not going in to "decel enlean" when throttle is closed while driving. With foot off gas, rpm will only drop to between 1000 and 1200. If I put the car back in gear, it will idle on as if my foot is on gas holding 1200 rpm even with throttle still closed. When the car comes to a full stop, idle will settle back to normal.
All parameters on scan tool are normal except this one. ECM is new. TPS is new and set at .54. MAF is a replacement from mid america. O2 is new Bosch. Only code I have is MAF Burnoff.
My snap-on scan tool manual says decel enlean is ebgaged based on several sensor inputs. Does anyone have any experience with this problem? I am suspecting issues with the MAF.
Thanks:
All parameters on scan tool are normal except this one. ECM is new. TPS is new and set at .54. MAF is a replacement from mid america. O2 is new Bosch. Only code I have is MAF Burnoff.
My snap-on scan tool manual says decel enlean is ebgaged based on several sensor inputs. Does anyone have any experience with this problem? I am suspecting issues with the MAF.
Thanks:
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Joined: Jun 2004
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
My car (stock '87) is not going in to "decel enlean" when throttle is closed while driving. With foot off gas, rpm will only drop to between 1000 and 1200. If I put the car back in gear, it will idle on as if my foot is on gas holding 1200 rpm even with throttle still closed. When the car comes to a full stop, idle will settle back to normal.
All parameters on scan tool are normal except this one. ECM is new. TPS is new and set at .54. MAF is a replacement from mid america. O2 is new Bosch. Only code I have is MAF Burnoff.
My snap-on scan tool manual says decel enlean is ebgaged based on several sensor inputs. Does anyone have any experience with this problem? I am suspecting issues with the MAF.
Thanks:
All parameters on scan tool are normal except this one. ECM is new. TPS is new and set at .54. MAF is a replacement from mid america. O2 is new Bosch. Only code I have is MAF Burnoff.
My snap-on scan tool manual says decel enlean is ebgaged based on several sensor inputs. Does anyone have any experience with this problem? I am suspecting issues with the MAF.
Thanks:
Thread Starter
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Joined: Mar 2009
Posts: 60
Likes: 1
From: Memphis TN
So, it does not engage if coasting down in neutral? If so, thanks.
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Joined: Apr 2002
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From: Anaheim CA
My car (stock '87) is not going in to "decel enlean" when throttle is closed while driving. With foot off gas, rpm will only drop to between 1000 and 1200. If I put the car back in gear, it will idle on as if my foot is on gas holding 1200 rpm even with throttle still closed. When the car comes to a full stop, idle will settle back to normal.
Thread Starter
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Joined: Mar 2009
Posts: 60
Likes: 1
From: Memphis TN
What you are seeing is "throttle follower mode". The IAC is opened as you mash down on the gas pedal. When you release the gas pedal the IAC is still open and keeps the engine from stalling as the throttle plates slam shut and airflow instantly goes to zero. Throttle follower mode looks at MPH and backs off on the IAC as the car slows to a stop.
Team Owner
Joined: Sep 2003
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GOOGLE "IAC throttle follower mode" for hundreds of explanations and theory.
You could certainly have issues but you need to rely on the scan device and the corresponding FSM diagnostics to confirm.
Do the diagnostics for the codes that you currently have displayed by the scanner and then revisit everything.
You could certainly have issues but you need to rely on the scan device and the corresponding FSM diagnostics to confirm.
Do the diagnostics for the codes that you currently have displayed by the scanner and then revisit everything.
Last edited by WVZR-1; Aug 1, 2016 at 07:59 AM.
Thread Starter
Advanced
Joined: Mar 2009
Posts: 60
Likes: 1
From: Memphis TN
GOOGLE "IAC throttle follower mode" for hundreds of explanations and theory.
You could certainly have issues but you need to rely on the scan device and the corresponding FSM diagnostics to confirm.
Do the diagnostics for the codes that you currently have displayed by the scanner and then revisit everything.
You could certainly have issues but you need to rely on the scan device and the corresponding FSM diagnostics to confirm.
Do the diagnostics for the codes that you currently have displayed by the scanner and then revisit everything.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
No. If it did, the engine would stall. It engages when the tires are driving the crankshaft above a certain speed (usually ~1200 RPM on my vehicles).
I DID have an '83 Trans Am that has CFI, and it would go into DFCO in neutral if you revved it up and cut the throttle. In that car you could watch the injectors shut of as the engine coasted down and fire back up as RPMS dropped to ~1200. But I don't think newer cars are as aggressive w/DFCO. My truck ('96 Silverado) takes about 3-4 seconds of in-gear, deceleration before it cuts fuel.
.
I DID have an '83 Trans Am that has CFI, and it would go into DFCO in neutral if you revved it up and cut the throttle. In that car you could watch the injectors shut of as the engine coasted down and fire back up as RPMS dropped to ~1200. But I don't think newer cars are as aggressive w/DFCO. My truck ('96 Silverado) takes about 3-4 seconds of in-gear, deceleration before it cuts fuel.
.
Last edited by Tom400CFI; Aug 1, 2016 at 03:39 PM.
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Thread Starter
Advanced
Joined: Mar 2009
Posts: 60
Likes: 1
From: Memphis TN
No. If it did, the engine would stall. It engages when the tires are driving the crankshaft above a certain speed (usually ~1200 RPM on my vehicles).
I DID have an '83 Trans Am that has CFI, and it would go into DFCO in neutral if you revved it up and cut the throttle. In that car you could watch the injectors shut of as the engine coasted down and fire back up as RPMS dropped to ~1200. But I don't think newer cars are as aggressive w/DFCO. My truck ('96 Silverado) takes about 3-4 seconds of in-gear, deceleration before it cuts fuel.
.
I DID have an '83 Trans Am that has CFI, and it would go into DFCO in neutral if you revved it up and cut the throttle. In that car you could watch the injectors shut of as the engine coasted down and fire back up as RPMS dropped to ~1200. But I don't think newer cars are as aggressive w/DFCO. My truck ('96 Silverado) takes about 3-4 seconds of in-gear, deceleration before it cuts fuel.
.