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Hi there,
This is my first TDI. I absolutely love diesels, so naturally I gravitated to the TDI (5-speed, of course!) as my choice for a fuel-efficient car. It now has 224k miles on it, but it still runs like a champ. That being said, a year ago, I noticed that the idling was a little rougher than normal, but it wasn't really noticeable, and if I put the A/C on, it idled like it was brand new. I just ignored it. About a month ago, it threw a (p0401, I think) OBDII code for the EGR sensor and really started chugging at an idle. I took the EGR valve off and cleaned it (there was a bit of buildup, but less than I expected for the mileage) and also attempted to clean the MAF sensor. Just for maintenance, I replaced all the vacuum lines since a few of them were showing signs of wear. After resetting the codes, it still idles a little rough (roughness goes away under any sort of load again) and the P0401 code is back. (I am assuming that, since the light popped right back on after about 20 miles)
As an interesting side-note, it idles perfectly until the engine is *almost* fully warmed up, and then it starts idling rough. For example, if I drive to town, (a full warm up) go into a store for about an hour, come back out, start my engine up and then start fiddling around with my phone or something, the engine will just start chugging at some point (~5 minutes) like a switch was flipped. So my theory is that it has to be something that is electronically regulated.
So I have a few related questions.
Thanks so much for your time!
Ryan Hoshor
Woodleaf, North Carolina
This is my first TDI. I absolutely love diesels, so naturally I gravitated to the TDI (5-speed, of course!) as my choice for a fuel-efficient car. It now has 224k miles on it, but it still runs like a champ. That being said, a year ago, I noticed that the idling was a little rougher than normal, but it wasn't really noticeable, and if I put the A/C on, it idled like it was brand new. I just ignored it. About a month ago, it threw a (p0401, I think) OBDII code for the EGR sensor and really started chugging at an idle. I took the EGR valve off and cleaned it (there was a bit of buildup, but less than I expected for the mileage) and also attempted to clean the MAF sensor. Just for maintenance, I replaced all the vacuum lines since a few of them were showing signs of wear. After resetting the codes, it still idles a little rough (roughness goes away under any sort of load again) and the P0401 code is back. (I am assuming that, since the light popped right back on after about 20 miles)
As an interesting side-note, it idles perfectly until the engine is *almost* fully warmed up, and then it starts idling rough. For example, if I drive to town, (a full warm up) go into a store for about an hour, come back out, start my engine up and then start fiddling around with my phone or something, the engine will just start chugging at some point (~5 minutes) like a switch was flipped. So my theory is that it has to be something that is electronically regulated.
So I have a few related questions.
- What sensor engages at almost full temperature, but the [possibly erroneous] readings are ignored before that point?
- I have heard that the idling problem is sometimes related to the MAF sensor. Should I replace that just for routine maintenance at this mileage even though it is not throwing a code? Do you recommend spending the extra and getting OEM, or is something like this ok: http://amzn.to/ensl8n ?
- Is it possible that the EGR Sensor/Valve is bad or failed? Is there a good way to test that, and if it has failed, would it even cause the rough idle?
- Are there other possible causes that are not showing up through OBDII?
Thanks so much for your time!
Ryan Hoshor
Woodleaf, North Carolina