Advice Need From the Experts
 

Hi guys,

So my 2004 XG was shuddering at redlights and shuddering worse at redlights with the A/C on. No check engine light, no codes. After research it all pointed to the EGR valve. While checking it I noticed that the vacuum lines would crumble whenever I touched them. So while waiting for the EGR valve to come in I matched up the vacuum hose size as best I could with lines from Autozone (I don't know where to order stock lines). After switching the lines the check engine light came on reading the P0401 code. EGR valve came in, I changed it and the car runs great. Intake looks clean.

After about 40 miles the check engine light came on again and of course it's P0401. So what do you guys think? Why would it come on again after changing the valve.

Could it be that the vacuum lines are not the right size?
Could it be the little jets within the lines? There was only one on the yellow striped line (are there suppose to be more?)
Could it be the t-connector for the yellow and green lines? I had to use a regular one from Autozone?

Any help would be appreciated.

Usually there is a vacuum diagram on the underside of the hood. Sometimes they show the lines using the original colors so they know where to go.
Vacuum hose is usally not expensive and while getting an assortment (2 feet if each size) will come in handy later on. It doesn't eat or go bad when stored.!

A side note , regular vacuum hose cannot be used to carry liquid fuel or vapor.
.

Have heard carbon bits can clog EGR
Clean EGR and associated hoses
Clear DTC codes and run
See if codes comes back

This should help
 

Ok had the same issue alone with a few others and was able to fix all of them, took sometime with a lot of headaches so i can tell you right now that the vacuum lines with the colored stripes are a MUST procured part solely from a Hyundai dealer.. The vacuum lines have restrictor's inside that will NOT be internal of the vacuum lines purchased from any other part store. I have placed the link below. Hopefully this helps..
https://www.hyundaipartsdeal.com/par...cuum_hose.html

Also i would like to add that even after i replaced the vacuum hoses with the factory required equipment the code changed to a code from the throttle body which i clean but still had the same issue and same rough idle and sputter. After intense troubleshooting i will share with you another problem that many overlook but points to the throttle body when that isn't the issue at all. So let me introduce you to a known problem that i have now found with about 3 other XG350 that i now own that had the exact same issue. This is the Plenum Intake Manifold which has fins on the inside to direct air and will give you a combination of codes if the PROPER COLORED VACUUM HOSES after install gives you another code.


https://cimg7.ibsrv.net/gimg/www.hyu...98379dc0ce.jpg
https://cimg2.ibsrv.net/gimg/www.hyu...f53e061206.jpg
https://cimg1.ibsrv.net/gimg/www.hyu...7f781b9bcb.jpg
https://cimg9.ibsrv.net/gimg/www.hyu...3c3d7b8391.jpg
https://cimg7.ibsrv.net/gimg/www.hyu...277ddf15d8.jpg

If you purchased replacement hoses from Hyundai, did you happen to check what type/size restrictor was in there?
Or in the old hoses ? Most of the time a restrictor is used in a vacuum line is to slow down the application of full vacuum immediately Sure could slow down the EGR valve opening . Most manufacturers have the valve with a smaller hole at the entrance instead of placing a restrictor in a hose. Thanks for the info.

Thanks! That’s a ton of information! I appreciate the help. I found one restrictor jet in one of the old hoses but the other ones did not. I think there is suppose to be two? I’ll check out the link. Thanks again!

One of the hoses had a restrictor in it (the yellow hose I believe) so I put it in the hose that I replaced. I think there is suppose to be more than one but I’m not sure. Thanks for the help!