Car idles better with A/C or Heater on?
12-13-2010, 10:54 PM
#1
Instructor
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Car idles better with A/C or Heater on?
Hi All, posted this in the C4 Tech section and they sugjested posting it here.
I've been doing a lot of work on my 1989 Corvette to help it idle better. When my car idles it sounds like the car is going to die, the eninge shakes and feelings like it stumbles trying to maintain RPM, I've actually had the car die while it's idling couple times, it slowly gets worse and worse until it just wants to die, not fun at a intersesction. Idle is at 600 to 700 RPM.
I've pinned the problem down to it only happening when I turn the Air Conditioning or the Heater off. When there on the idle is smooth.
I would imagine when the A/C or Heater is on it puts more demand on the engine making it run faster with makes for the idle smoother. Is there anything I can do to make the engine run "faster/smoother" when the A/C or Heater is off?
Any ideas?
Things I've replaced to fix the problem:
Injectors
O2 sensor
IAC
TPS (Set correctly)
Air Filter
CAT and Mufflers
ECM (Still has old EPROM in it)
All ignition system from plugs to inginition module
Did compression test and engine is good.
UPDATE:
Just did something interesting.... I checked my timing and noticed that when my EST wire (the wire by the brake booster that you disconnect to check the timing) was disconnected to check the timing the shake and stumble was gone...... Its like the computer is causing the shake stumble by adjusting the idle all the time.. Timeing was at the number top number 4 mark by the way on the pully.
Is it ok to drive with out the EST wire connected..? Can anyone think of why the car would be adjusting and causing the shake stumble with the EST connected?
I've been doing a lot of work on my 1989 Corvette to help it idle better. When my car idles it sounds like the car is going to die, the eninge shakes and feelings like it stumbles trying to maintain RPM, I've actually had the car die while it's idling couple times, it slowly gets worse and worse until it just wants to die, not fun at a intersesction. Idle is at 600 to 700 RPM.
I've pinned the problem down to it only happening when I turn the Air Conditioning or the Heater off. When there on the idle is smooth.
I would imagine when the A/C or Heater is on it puts more demand on the engine making it run faster with makes for the idle smoother. Is there anything I can do to make the engine run "faster/smoother" when the A/C or Heater is off?
Any ideas?
Things I've replaced to fix the problem:
Injectors
O2 sensor
IAC
TPS (Set correctly)
Air Filter
CAT and Mufflers
ECM (Still has old EPROM in it)
All ignition system from plugs to inginition module
Did compression test and engine is good.
UPDATE:
Just did something interesting.... I checked my timing and noticed that when my EST wire (the wire by the brake booster that you disconnect to check the timing) was disconnected to check the timing the shake and stumble was gone...... Its like the computer is causing the shake stumble by adjusting the idle all the time.. Timeing was at the number top number 4 mark by the way on the pully.
Is it ok to drive with out the EST wire connected..? Can anyone think of why the car would be adjusting and causing the shake stumble with the EST connected?
12-15-2010, 04:41 AM
#2
well, i had semillar problem with my 91 vette, it end up benig very easy to get fixed, simply i just needed to relearn the idle, with other words: re adjusting the idle screw on the throttle body and adjusting the tps, and here is a link on how to do that with the propper way:
http://www.corvetteactioncenter.com/...and+Idle+Speed
but u need to adjust the timing too according to ur car's spec which on mine is 6 degrees btcd
http://www.corvetteactioncenter.com/...and+Idle+Speed
but u need to adjust the timing too according to ur car's spec which on mine is 6 degrees btcd
Last edited by Ricky 91 vette; 12-15-2010 at 04:44 AM.
12-26-2010, 07:14 AM
#3
Hi All, posted this in the C4 Tech section and they sugjested posting it here.
I've been doing a lot of work on my 1989 Corvette to help it idle better. When my car idles it sounds like the car is going to die, the eninge shakes and feelings like it stumbles trying to maintain RPM, I've actually had the car die while it's idling couple times, it slowly gets worse and worse until it just wants to die, not fun at a intersesction. Idle is at 600 to 700 RPM.
I've pinned the problem down to it only happening when I turn the Air Conditioning or the Heater off. When there on the idle is smooth.
I would imagine when the A/C or Heater is on it puts more demand on the engine making it run faster with makes for the idle smoother. Is there anything I can do to make the engine run "faster/smoother" when the A/C or Heater is off?
Any ideas?
Things I've replaced to fix the problem:
Injectors
O2 sensor
IAC
TPS (Set correctly)
Air Filter
CAT and Mufflers
ECM (Still has old EPROM in it)
All ignition system from plugs to inginition module
Did compression test and engine is good.
UPDATE:
Just did something interesting.... I checked my timing and noticed that when my EST wire (the wire by the brake booster that you disconnect to check the timing) was disconnected to check the timing the shake and stumble was gone...... Its like the computer is causing the shake stumble by adjusting the idle all the time.. Timeing was at the number top number 4 mark by the way on the pully.
Is it ok to drive with out the EST wire connected..? Can anyone think of why the car would be adjusting and causing the shake stumble with the EST connected?
I've been doing a lot of work on my 1989 Corvette to help it idle better. When my car idles it sounds like the car is going to die, the eninge shakes and feelings like it stumbles trying to maintain RPM, I've actually had the car die while it's idling couple times, it slowly gets worse and worse until it just wants to die, not fun at a intersesction. Idle is at 600 to 700 RPM.
I've pinned the problem down to it only happening when I turn the Air Conditioning or the Heater off. When there on the idle is smooth.
I would imagine when the A/C or Heater is on it puts more demand on the engine making it run faster with makes for the idle smoother. Is there anything I can do to make the engine run "faster/smoother" when the A/C or Heater is off?
Any ideas?
Things I've replaced to fix the problem:
Injectors
O2 sensor
IAC
TPS (Set correctly)
Air Filter
CAT and Mufflers
ECM (Still has old EPROM in it)
All ignition system from plugs to inginition module
Did compression test and engine is good.
UPDATE:
Just did something interesting.... I checked my timing and noticed that when my EST wire (the wire by the brake booster that you disconnect to check the timing) was disconnected to check the timing the shake and stumble was gone...... Its like the computer is causing the shake stumble by adjusting the idle all the time.. Timeing was at the number top number 4 mark by the way on the pully.
Is it ok to drive with out the EST wire connected..? Can anyone think of why the car would be adjusting and causing the shake stumble with the EST connected?
12-29-2010, 02:58 PM
#4
Le Mans Master
You need to scan it to see the a/c request and what that does to pulse width and load; then compare it to non a/c. I'd guess your ECM isn't responding when it's off meaning you need a new one (because it thinks the a/c is still on - so it raises idle and adds fuel/then drops it because the load isn't there) but without any data, it's just a guess.
12-30-2010, 09:50 AM
#5
Burning Brakes
You Could (this is also a guess, of sorts) have a vacuum leak in the HVAC system that "goes away" when different control positions are selected. Perhaps a leak at one of the control "motors" or the vacuum line to it.
Something that would mean you have a leak in vent position, but no leak in A/C, for example.
This obviously doesn't have anything to do with the EST signal wire. Although - with that wire disconnected there is no ECM timing advance, meaning that you are then idling at a "retarded" ignition advance setting. That would be less sensitive to A/F ratio problems, such as a vacuum leak, perhaps.
And, Yes, you can Drive the car with the EST wire disconnected, and you won't Hurt anything, but it won't run well - there will be NO ignition advance happening at all.
Something that would mean you have a leak in vent position, but no leak in A/C, for example.
This obviously doesn't have anything to do with the EST signal wire. Although - with that wire disconnected there is no ECM timing advance, meaning that you are then idling at a "retarded" ignition advance setting. That would be less sensitive to A/F ratio problems, such as a vacuum leak, perhaps.
And, Yes, you can Drive the car with the EST wire disconnected, and you won't Hurt anything, but it won't run well - there will be NO ignition advance happening at all.
12-30-2010, 07:20 PM
#6
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You Could (this is also a guess, of sorts) have a vacuum leak in the HVAC system that "goes away" when different control positions are selected. Perhaps a leak at one of the control "motors" or the vacuum line to it.
Something that would mean you have a leak in vent position, but no leak in A/C, for example.
This obviously doesn't have anything to do with the EST signal wire. Although - with that wire disconnected there is no ECM timing advance, meaning that you are then idling at a "retarded" ignition advance setting. That would be less sensitive to A/F ratio problems, such as a vacuum leak, perhaps.
And, Yes, you can Drive the car with the EST wire disconnected, and you won't Hurt anything, but it won't run well - there will be NO ignition advance happening at all.
Something that would mean you have a leak in vent position, but no leak in A/C, for example.
This obviously doesn't have anything to do with the EST signal wire. Although - with that wire disconnected there is no ECM timing advance, meaning that you are then idling at a "retarded" ignition advance setting. That would be less sensitive to A/F ratio problems, such as a vacuum leak, perhaps.
And, Yes, you can Drive the car with the EST wire disconnected, and you won't Hurt anything, but it won't run well - there will be NO ignition advance happening at all.
****Breaking news!!****
I got frustrated and decided to mess with the timing. I unpluged the Dist wire and several settings set the timing to 0 degrees, then plugged the computer back in etc. Now the car does not stumble or shake or surge at idle weather the A/C is on or not..
Don't know if this hurts the car but it sure is driving good...
12-31-2010, 08:07 AM
#7
Base timing should be at 6 degrees BTDC. If the bypass wire is left disconnected then you'll set a code 42. Try setting the base timing to 6 if you feel like checking it out and see what it does.
Last edited by Solderhead; 12-31-2010 at 08:14 AM. Reason: clarification.
12-31-2010, 01:09 PM
#9
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12-31-2010, 01:16 PM
#10
Le Mans Master
Running around with the timing wire disconnected has it running on Backup which is working. However, doing closed loop, the ECM either has garbage flowing into it which creates the surge (more than likely on the a/c input) or it's toast. A 2 degree difference in timing isn't anything that a functioning system can't handle and a slipped balancer doesn't change timing - that has to be done manually.
