Code 334...new EGR valve...ROUGH idle?
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Senior User
Joined: Dec 2008
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From: Mckinleyville, CA
Code 334...new EGR valve...ROUGH idle?
Ok, so 6 months ago, I was having an EGR issue, I replaced it, problem was fixed. But, 1 month ago, I started having a rough idle and sporadic CEL. It has gotten so bad recetntly, the truck surges a couple times and then goes when you lightly get on the throttle. Pulled the codes and I was having codes 172, 173, 327, 328, 334... From another post we came to the conclusion that I should remove the EGR and clean it. I replaced the whole EGR valve under warranty. Eh...slight problem...I still have a rough idle but now I only have a code 334...A suggestion was given to do a vacuum test to the EGR, but I was hoping there might be something else I could check...seeing as how I'm pretty sure 2 new EGR's rule out the egr being the issue. Rough idle remains with the vacuum line connected or not. Advice?
Fleet Owner
Joined: Oct 2005
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From: Kentucky
For the DTC 334, pull and plug the vacuum line at the EGR valve. Back probe the EVP sensor to verify the reading is beween .2V and .67 VDC. If it is, re-attach the vacuum line, if it rises above .67 VDC, there is your culprit. There should be no vacuum applied to the EGR valve at idle. Take a look at the EVR solenoid, it is allowing vacuum through when it should not be applied.
If the EVP signal is above .67VDC with no vacuum applied, I would go after the EVP sensor in light of the two EGR valves you have swapped in.
The rough idle issue could be plugs, wires, cap, rotor, coil, poor routing of the plug wires causing cross-fire, dirty injectors, weak or dead cylinder, low fuel pressure. The list goes on.
If the EVP signal is above .67VDC with no vacuum applied, I would go after the EVP sensor in light of the two EGR valves you have swapped in.
The rough idle issue could be plugs, wires, cap, rotor, coil, poor routing of the plug wires causing cross-fire, dirty injectors, weak or dead cylinder, low fuel pressure. The list goes on.
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Senior User
Joined: Dec 2008
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From: Mckinleyville, CA
I will check that. It could also be the tune up I did a year ago, I never did check to see if I routed the plug wires properly to inhibit cross firing. I need to search for a wire routing diagram. Thanks.
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Joined: Apr 2018
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I've been chasing code 327 in my 1994 F350 w/the 460 FI. Replaced the EGR (tough to get out - found bolt release spray that did the trick), EVR, all new vacuum lines (the original plastic ones snapped when I barely touched them) and new EGR solenoid. Code finally gone but now am getting code 334 and 337. Idle is running too high. Keep tweaking the timing but not the right fix. Seems like I still have a vacuum problem, so I'm interested to see if your fix worked.
Cargo Master
Joined: Jun 2013
Posts: 3,182
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From: Somewhere n North America
I've been chasing code 327 in my 1994 F350 w/the 460 FI. Replaced the EGR (tough to get out - found bolt release spray that did the trick), EVR, all new vacuum lines (the original plastic ones snapped when I barely touched them) and new EGR solenoid. Code finally gone but now am getting code 334 and 337. Idle is running too high. Keep tweaking the timing but not the right fix. Seems like I still have a vacuum problem, so I'm interested to see if your fix worked.
If you are just following, then no worries...
5th Wheeling
Joined: Dec 2010
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Rough Idle too
I also have a 1994 460 f250 and it has the same thing rough idle I have changed the spark plugs wires and distributor..It started when I used the back tank which when dropped and cleaned out had all sorts of crap due to the air vent thing on top not been on...I was able to put on with the tank off (hard to get int there) it made my engine miss and have no power to go over 45-50 AND this was towing my 22 ft fifth wheel...I figured after the cleaning and running a bunch of Lucas cleaner in the gas it would get better and it did for a bit..NOT GREAT but better from the front tank...Once after cleaning the back tank etc etc I put some gas tried the rear tank again and it is a bit better but not like before and the miss seems to be at the 1000-1400 RPM, i checked the spark plugs, made sure they were not crossed etc but now it is running worse so I am thinking something in the ignition or fuel but they are both new and new fuel filter too..ANY ideas are very welcome at this point as I am going to need to tow my 11000 big fifth wheel to the Grand Canyon in a few weeks and want to do over 15 MPH
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Logistics Pro
Joined: Mar 2005
Posts: 4,698
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From: Mexico, Missouri
Start by checking for codes.
And I would also start a new thread for your problem as this one is 8 years old. You will get a lot more feedback and help.
Google pulling codes for Ford OBD1.
And I would also start a new thread for your problem as this one is 8 years old. You will get a lot more feedback and help.
Google pulling codes for Ford OBD1.
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