Bac And Acv Removal
04-16-2004, 08:10 PM
#1
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Thread Starter
Join Date: Mar 2003
Posts: 52
This may be a stupid question but. . .
As I understand it the bac and acv let extra air into the engine when the ecu wants to raise the idle, either because of a/c, cold weather, or whatever. The ecu then injects more fuel to compensate for the added air. So, if you remove these valves, when the ecu goes to raise the idle, no extra air will be added because the bac and acv have been removed, but won't the ecu still add more fuel making the car run way too rich?
Basically, I want my 1990 NA to idle less eratically (it revs itself to 1500 rpm, then drops all the way down, almost stalls, then comes back up. It happens when the car starts cold or whenever else it feels like it). I have done the TB mod and will remove the bac and acv if it will fix the idle. I just want to understand what I am doing before I go ripping things out of my car. Also, will i run into problems removing the acv but still keeping the airpump? I need the airpump because of the 6 ports and vdi.
As I understand it the bac and acv let extra air into the engine when the ecu wants to raise the idle, either because of a/c, cold weather, or whatever. The ecu then injects more fuel to compensate for the added air. So, if you remove these valves, when the ecu goes to raise the idle, no extra air will be added because the bac and acv have been removed, but won't the ecu still add more fuel making the car run way too rich?
Basically, I want my 1990 NA to idle less eratically (it revs itself to 1500 rpm, then drops all the way down, almost stalls, then comes back up. It happens when the car starts cold or whenever else it feels like it). I have done the TB mod and will remove the bac and acv if it will fix the idle. I just want to understand what I am doing before I go ripping things out of my car. Also, will i run into problems removing the acv but still keeping the airpump? I need the airpump because of the 6 ports and vdi.
04-16-2004, 09:02 PM
#2
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Join Date: Aug 2002
Location: Eastern PA
Posts: 1,801
Your air control valve is for emissions, that controls the air being pumped into the cats from the air pump, usually when one is taken out, you take out the other. I'm not sure how that will affect the vdi but it shouldn't be affecting your idle probs. The bac when working right should compensate for electric loads like a/c etc like you said. Taking that out wont help your idle problem either unless its bad to begin with. I think your idle problem may be from the TB mod. Did you disconnect the thermowax? The thermowax holds your throttle open until the coolant heats up enough to melt it. You may have a vac leak someplace. I'd check for that first and make sure your throttle plates are closing properly on the dashpot. Make sure your TPS and idle were set back to spec after the TB mod.
There should be some of this in the FAQ section.
There should be some of this in the FAQ section.
04-17-2004, 03:29 AM
#3
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Join Date: Dec 2002
Location: QUEENS NYC
Posts: 1,687
Originally Posted by IHEnter' date='Apr 16 2004, 05:10 PM
This may be a stupid question but. . .
As I understand it the bac and acv let extra air into the engine when the ecu wants to raise the idle, either because of a/c, cold weather, or whatever. The ecu then injects more fuel to compensate for the added air. So, if you remove these valves, when the ecu goes to raise the idle, no extra air will be added because the bac and acv have been removed, but won't the ecu still add more fuel making the car run way too rich?
Basically, I want my 1990 NA to idle less eratically (it revs itself to 1500 rpm, then drops all the way down, almost stalls, then comes back up. It happens when the car starts cold or whenever else it feels like it). I have done the TB mod and will remove the bac and acv if it will fix the idle. I just want to understand what I am doing before I go ripping things out of my car. Also, will i run into problems removing the acv but still keeping the airpump? I need the airpump because of the 6 ports and vdi.
As I understand it the bac and acv let extra air into the engine when the ecu wants to raise the idle, either because of a/c, cold weather, or whatever. The ecu then injects more fuel to compensate for the added air. So, if you remove these valves, when the ecu goes to raise the idle, no extra air will be added because the bac and acv have been removed, but won't the ecu still add more fuel making the car run way too rich?
Basically, I want my 1990 NA to idle less eratically (it revs itself to 1500 rpm, then drops all the way down, almost stalls, then comes back up. It happens when the car starts cold or whenever else it feels like it). I have done the TB mod and will remove the bac and acv if it will fix the idle. I just want to understand what I am doing before I go ripping things out of my car. Also, will i run into problems removing the acv but still keeping the airpump? I need the airpump because of the 6 ports and vdi.
Then when im driving and i hit the brakes the rpms goes down to like 300rpm and when i let go it shoots back up to like 750-1000rpm
So waht do i have to do to the BAC to fix dat
04-17-2004, 04:56 PM
#4
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Thread Starter
Join Date: Mar 2003
Posts: 52
Possibly the bac is bad or it may be just a tps adjustment. Either way i am going to buy the block off plates and remove both the bac and acv. I will let you know if that fixes the problem.
Also, the thermowax was removed when i did the tb mod so that can't be the problem.
Also, the thermowax was removed when i did the tb mod so that can't be the problem.
04-22-2004, 08:39 PM
#7
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Join Date: Mar 2003
Posts: 52
04-22-2004, 09:07 PM
#9
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Join Date: Jul 2003
Location: MN
Posts: 392
I have had a surging problem for awhile now. I've set my TPS to a T and it didn't do anything for me. It doesn't come close to stalling though, it just revs at idle from 1k to 1500 over and over. I've checked over for vaccume leaks many many times, TPS, idle adjustment screw and all. Sometime I can get it to stop by playing with the BAC adjustment, but it only works for a couple days and then it starts doing it again. Might just remove the BAC and see what happens, i got a k2rd plate sittin around.
04-23-2004, 05:32 PM
#10
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Join Date: May 2003
Posts: 1,784
Originally Posted by TII777' date='Apr 22 2004, 06:07 PM
I have had a surging problem for awhile now. I've set my TPS to a T and it didn't do anything for me. It doesn't come close to stalling though, it just revs at idle from 1k to 1500 over and over. I've checked over for vaccume leaks many many times, TPS, idle adjustment screw and all. Sometime I can get it to stop by playing with the BAC adjustment, but it only works for a couple days and then it starts doing it again. Might just remove the BAC and see what happens, i got a k2rd plate sittin around.