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P0401 EGR Flow Insufficient Solved

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Old Feb 12, 2011, 09:13 PM
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P0401 EGR Flow Insufficient Solved

Hello,

I have been struggling with a p0401 for a couple of months.

My car has been idling very bad, initially upon startup, it would idle ok, vac guage around 18in/Hg at >1000rpm. After a minute or so the idle would drop to 900rpm and my vac would go to ~10in/HG and a rough idle would occur. CES light would come on with P0401 eventually after a few driving cycles.

I changed the EGR valve even though it would open and close when I applied vacuum from an external pump, the intake manifold inlets were also clear. With the EGR valve changed out for a new one the problem persisted.

I bought an EGR vacuum solenoid valve and installed it tonight ($70 from Rock Auto). So far it seems to have fixed my problem, the car runs well and the idle is good. It idles around 900rpm at about 18"/Hg.

My car is an 04 Evo with 107,000 miles. AMS tuned with 264in/272ex HKS cams, AMS Turbo Back Exhaust and some suspension mods plus minor stuff.

The point of this thread is to help others who may have a p0401 code who are struggling to fix it. My fix was to replace the EGR vacuum solenoid valve.
Old Feb 13, 2011, 08:08 AM
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Good to know thanks for sharing.
Old Feb 13, 2011, 08:12 AM
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could just delete the entire egr system and turn off the periphery bits in the rom
Old Feb 13, 2011, 11:30 AM
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^ tomorrow's project for me... i hate soot filled intake manifolds.

Glad you fixed the issue.
Old Feb 13, 2011, 04:02 PM
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Good job! It's always nice to have your vehicle running right.


Originally Posted by milford
could just delete the entire egr system and turn off the periphery bits in the rom
How do you adjust for proper operation during engine warm-up?
Old Apr 29, 2011, 11:36 AM
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Had the same problem. I had the blasted vacuum hose fly off like many others did. Don't forget to ziptie that sucker down!
Old Jun 6, 2011, 10:35 AM
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Originally Posted by euntaeyi
Had the same problem. I had the blasted vacuum hose fly off like many others did. Don't forget to ziptie that sucker down!
Which vacuum line, i just had this code start yesterday will driving. cant find the line that popped off though. thanks in advance!
Old Jun 6, 2011, 10:47 AM
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Bottom of the back of the intake manifold on the driverside.
Old Jun 6, 2011, 11:02 AM
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Originally Posted by mirkendargen
Bottom of the back of the intake manifold on the driverside.
thanks you, I checked there and just found the passenger side smaller hose disconnected
Old Jun 6, 2011, 11:10 AM
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The fuel pressure regulator hose? That could have been bad!
Old Jul 18, 2011, 01:09 PM
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ok same code. were do i start?
Old Jul 18, 2011, 01:23 PM
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same code p0401. were do i start looking?
Old Oct 1, 2011, 08:34 AM
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Buying new valve just got this code.
Old Oct 1, 2011, 11:55 PM
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Check all the vacuum lines going into the EGR, they pop off under boost.

N
Old Oct 14, 2011, 01:21 PM
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Originally Posted by xXxJIGGAxXx
Hello,

I have been struggling with a p0401 for a couple of months.

My car has been idling very bad, initially upon startup, it would idle ok, vac guage around 18in/Hg at >1000rpm. After a minute or so the idle would drop to 900rpm and my vac would go to ~10in/HG and a rough idle would occur. CES light would come on with P0401 eventually after a few driving cycles.

I changed the EGR valve even though it would open and close when I applied vacuum from an external pump, the intake manifold inlets were also clear. With the EGR valve changed out for a new one the problem persisted.

I bought an EGR vacuum solenoid valve and installed it tonight ($70 from Rock Auto). So far it seems to have fixed my problem, the car runs well and the idle is good. It idles around 900rpm at about 18"/Hg.

My car is an 04 Evo with 107,000 miles. AMS tuned with 264in/272ex HKS cams, AMS Turbo Back Exhaust and some suspension mods plus minor stuff.

The point of this thread is to help others who may have a p0401 code who are struggling to fix it. My fix was to replace the EGR vacuum solenoid valve.
This happened to me today. My problem was just the vacuum hose slipping off the EGR valve. Superglued and zip tied, good to go!


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