Source of my problems?
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Logistics Pro
Joined: Mar 2001
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Source of my problems?
I have been having some rough idling problems and I got around to testing the choke pull off and EGR. Both will not hold any vacuum whatsoever. I can blow air easily into a hose connected both items with ease. I assume these are big source of a vacuum leak? Will a non-functioning EGR cause idling problems?
Postmaster
Joined: Jul 2001
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From: MD
Malfunctioning chokes rarely cause rough idle.
Stuck EGR valves will cause rough idle and power less. The proper way to test the EGR is to disconnect its vacuum source then plug the hose. Hook it up to a hand vacuum pump. If the EGR is working properly, it should idle very rough or die when vacuum is applied from the vacuum pump.
Stuck EGR valves will cause rough idle and power less. The proper way to test the EGR is to disconnect its vacuum source then plug the hose. Hook it up to a hand vacuum pump. If the EGR is working properly, it should idle very rough or die when vacuum is applied from the vacuum pump.
Thread Starter
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Logistics Pro
Joined: Mar 2001
Posts: 4,157
Likes: 3
Malfunctioning chokes rarely cause rough idle.
Stuck EGR valves will cause rough idle and power less. The proper way to test the EGR is to disconnect its vacuum source then plug the hose. Hook it up to a hand vacuum pump. If the EGR is working properly, it should idle very rough or die when vacuum is applied from the vacuum pump.
Stuck EGR valves will cause rough idle and power less. The proper way to test the EGR is to disconnect its vacuum source then plug the hose. Hook it up to a hand vacuum pump. If the EGR is working properly, it should idle very rough or die when vacuum is applied from the vacuum pump.
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
Once the engine is warmed up and the choke is open, the choke pulloff is out of the equation. The only problem it could cause in this case is a vacuum leak.
If your EGR valve won't hold vacuum, then you won't be able to test it to see if it's stuck open at idle. The EGR valve can cause a rough idle by being stuck open at idle (which isn't supposed to happen), but if you can't get yours to move then you can't tell if it's stuck. The most common problem with EGR valves is that the diaphragm ruptures and they can't open; it's less common for them to stick open (that usually happens because of carbon buildup, which prevents the spindle from seating in the bore).
You should replace both of these items for other reasons, but I doubt either will solve the idle problem. At least you'll be able to take them out of the equation - it's hard to solve a problem with this many variables. Have you checked the obvious, like vacuum level and timing? It seems like I remember you putting a vacuum gauge on it not too long ago and that seemed fine. Do you know where your idle speed is at? Is the rough idle related to engine temperature? For example, does it only happen when the engine is cold, or is it all the time?
If your EGR valve won't hold vacuum, then you won't be able to test it to see if it's stuck open at idle. The EGR valve can cause a rough idle by being stuck open at idle (which isn't supposed to happen), but if you can't get yours to move then you can't tell if it's stuck. The most common problem with EGR valves is that the diaphragm ruptures and they can't open; it's less common for them to stick open (that usually happens because of carbon buildup, which prevents the spindle from seating in the bore).
You should replace both of these items for other reasons, but I doubt either will solve the idle problem. At least you'll be able to take them out of the equation - it's hard to solve a problem with this many variables. Have you checked the obvious, like vacuum level and timing? It seems like I remember you putting a vacuum gauge on it not too long ago and that seemed fine. Do you know where your idle speed is at? Is the rough idle related to engine temperature? For example, does it only happen when the engine is cold, or is it all the time?
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Logistics Pro
Joined: Mar 2001
Posts: 4,157
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Once the engine is warmed up and the choke is open, the choke pulloff is out of the equation. The only problem it could cause in this case is a vacuum leak.
If your EGR valve won't hold vacuum, then you won't be able to test it to see if it's stuck open at idle. The EGR valve can cause a rough idle by being stuck open at idle (which isn't supposed to happen), but if you can't get yours to move then you can't tell if it's stuck. The most common problem with EGR valves is that the diaphragm ruptures and they can't open; it's less common for them to stick open (that usually happens because of carbon buildup, which prevents the spindle from seating in the bore).
You should replace both of these items for other reasons, but I doubt either will solve the idle problem. At least you'll be able to take them out of the equation - it's hard to solve a problem with this many variables. Have you checked the obvious, like vacuum level and timing? It seems like I remember you putting a vacuum gauge on it not too long ago and that seemed fine. Do you know where your idle speed is at? Is the rough idle related to engine temperature? For example, does it only happen when the engine is cold, or is it all the time?
If your EGR valve won't hold vacuum, then you won't be able to test it to see if it's stuck open at idle. The EGR valve can cause a rough idle by being stuck open at idle (which isn't supposed to happen), but if you can't get yours to move then you can't tell if it's stuck. The most common problem with EGR valves is that the diaphragm ruptures and they can't open; it's less common for them to stick open (that usually happens because of carbon buildup, which prevents the spindle from seating in the bore).
You should replace both of these items for other reasons, but I doubt either will solve the idle problem. At least you'll be able to take them out of the equation - it's hard to solve a problem with this many variables. Have you checked the obvious, like vacuum level and timing? It seems like I remember you putting a vacuum gauge on it not too long ago and that seemed fine. Do you know where your idle speed is at? Is the rough idle related to engine temperature? For example, does it only happen when the engine is cold, or is it all the time?
Thanks. Because the EGR diaphragm is shot, it is stuck in the downward(towards carb) position-not sure if that is open or closed.
The vacuum was decent 20-22 and pretty steady before my idling problems got much worse recently. Now it's jumpy around 15-18 and more stumbling than before.
Timing is off by only 2 degrees. I will replace both of these items and then I can goto the next step.
Would you know where a good place to get the EGR valve?
Postmaster
Joined: Jul 2001
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From: MD
Ignore the gauge. Just pump constantly until the engine's behavior change. If it does not, it's a pretty good indicator the EGR valve went south.
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Logistics Pro
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Yeah, nothing. I can't pump till the cows come home, no change, no movement.
