Rough Idle and Loss of 3-5mpg after egr replacement?

G Men 08

Veteran Member
Joined
Jun 15, 2010
Location
NY
TDI
MK4 Golf 5 spd
I replaced my EGR valve due to the insufficient flow CEL.

Good news is that the CEL is gone, and she passed inspection!

Bad news is that for the first 30 seconds or so after the engine starts, the idle fluctuates roughly 100rpm, as well as a mpg decrease of around 3mpg+?

I've only went through 1 full tank of fuel since the valve replacement so at first I though that it may have been my lead foot. But after carefully observing the miles put on, as opposed to fuel consumption per half tank (religiously touch if not exceed 250 miles per half tank by the time the needle moves off of the half full line) I barely got to 230 miles which leads me to think I will be lucky to reach 450 miles to this tank. (normally 500 miles +/- 10 miles)

Am I missing something as far as an adaptation or re-learning a parameter in VAG-COM due to the new valve?
 

nord

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Mar 5, 2010
Location
Southern Tier NY
TDI
All turned back to VW. Now a 2017 Hundai Tuscon. Not a single squalk in 10k miles.
I'll start with the basics which you're entirely free to disregard. The problem being that if you disregard, then you won't be able to eliminate.

Change your fuel filter at minimum. Make sure there is no water in the bowl and no "glitter" on the top of the filter when you remove the cap. ( There won't be glitter but check anyway,) Make 100% sure that your lift pump is operational.

At least check your air filter. If it's modified (K&N or such) and uses oil as a filter medium, you may assume a contaminated MAF.

EGR valves are fun devices prone to hidden failures. Three distinct components of the valve have to work in concert. The actuator motor drives the valve and also the sensor. The sensor sends info to the ECU. The ECU then adjusts the EGR valve while monitoring both charge air and exhaust.

My personal experience is that the system is far from being perfect. In my case I experienced stalling and hard starts after a stall. I also was vaguely aware of a loss of power at times, but not limp mode. Fuel economy suffered and once in awhile white smoke. But no CEL until much later in the game.

When I finally got a CEL and thus error codes it at first didn't make sense. The ECU flagged a MAF problem. VagCom disagreed on that point as I could see that the MAF was working. The MAF being eliminated, logic had to be used. What else is tied to the intake system?

The answer was the EGR valve. It looked like it worked. The valve seemed to open and close properly, and the ECU seemed happy with the info being received. The test was actually very simple as I still suspected the valve... I made sure the valve body was closed and disconnected the electrics. The ECU immediately flagged the disconnect but the car began to run flawlessly.

My conclusion? The ECU was actually correct as there was an airflow issue. The problem being that the ECU had no reason to suspect a bad EGR valve and thus assumed a problem with intake air. This was actually correct but the MAF was not at fault. It all made sense.

Close your EGR valve. Make sure it isn't leaking then disconnect the electrical connection. You'll set a CEL but if the valve is the issue your engine should now run nicely. If it does, then you'll know. If not, then no harm done and you can eliminate the valve.

As to economy there are at least a couple of factors coming into play. First is winter fuel. 3 mpg is well within what might be expected. Further, a failing MAF or EGR valve will also drop economy. My guess as far as issues other than fuel is either a failing MAF or a EGR valve which isn't working properly.
 

Rembrant

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Joined
Oct 31, 2014
Location
Canada's Ocean Playground
TDI
2013 Golf TDI DSG
Bad news is that for the first 30 seconds or so after the engine starts, the idle fluctuates roughly 100rpm, as well as a mpg decrease of around 3mpg+?
Have you tried to disconnect the vacuum from the new valve to see if the idle goes back to normal? You can just plug the vacuum line temporarily.

It would be nice to watch the MAF numbers while idling to see if there is a fluctuation there...

500 miles per tank? How many gallons do you usually put in for a fill-up? I assume non-vented?
 

UhOh

Top Post Dawg
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Dec 24, 2014
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PNW
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2000 & 2003 Golf GLS
What did the old EGR look like vis a vis build-up? And what did the intake look like? Would like to rule out having knocked loose any carbon debris into the intake and engine/head.

Did you install a new O-ring between the EGR valve and intake manifold? And, did you properly get all the bolts (3) in and tightened? (been cases where even shops fail to do this!) And for the EGR cooler as well?

Double-check your vacuum hoses. The one to the ASV (plastic nipple) is kind of easy to get connected poorly.
 

G Men 08

Veteran Member
Joined
Jun 15, 2010
Location
NY
TDI
MK4 Golf 5 spd
The intake and all components was cleaned, timing belt was done, new turbo, rebuilt head, oil/coolant seals o rings and gaskets all replaced within the last 15k miles.

Fuel filter was done maybe 2k miles ago.

The old egr valve looked great, other than oily residue. I believe that I ruined the old egr valve when I had everything apart to clean for intake build up. I let it all soak in MEK (which worked great btw, just be extremely cautious while using and be sure to look into the proper PPE while using)
 

G Men 08

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Location
NY
TDI
MK4 Golf 5 spd
Vacuum hoses will be checked and verified here shortly.

And to clarify, the rough idle is only for the first 30 seconds or so after a cold start up. It never did this until I replaced the EGR valve.
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS
Is the starting issue only when it's sat for a while rather than when the ambient temps are cold?

If you have a MityVac check the operation of the EGR valve itself. Pulling a vacuum on the top vacuum chamber (metal) should cause the valve to drop from the bottom of the unit (if you look in with the hose popped off). Either it's a DOA unit or there's leak going on. A leak, however, would to result in a more persistent issue.

And then again it's possible that it's an entirely different issue (injector, or other fuel delivery issue) that has just managed to manifest itself.
 

G Men 08

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Jun 15, 2010
Location
NY
TDI
MK4 Golf 5 spd
Yes UhOh, when the car has sat for a period of time. I'll have to dig out vag com as well to check the egr valve function. Hopefully I get the time to check it with my mityvac tomorrow.
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS
OK, it sounds like you've got a vacuum or air leak (fuel side). Since this issue popped up following the replacement of the EGR valve then I'd tend to suspect a vacuum hose is either bad or is not seated well; also, are we sure the vacuum hoses are connected/routed as they're supposed to be?
 

G Men 08

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Joined
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Location
NY
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MK4 Golf 5 spd
I just verified that the EGR valve diaphragm opens at around 7in vacuum, and progressively opens and holds with more vacuum.

All hardware is tight, and I did use new gaskets (paper and metal) for new EGR replacement.

Both of the vacuum hoses are installed, one on the ASV, the other for the EGR valve.

My next step is to check the values via VAGCOM. Which functions would you recommend I check, aside from EGR function?


FWIW, the car sat in sub 50 degree weather for around 2-2.5 hours without being started. When I first went out to investigate I started the engine to see if the idle hesitation happened, it did not.
 

G Men 08

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Location
NY
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MK4 Golf 5 spd
OK, it sounds like you've got a vacuum or air leak (fuel side). Since this issue popped up following the replacement of the EGR valve then I'd tend to suspect a vacuum hose is either bad or is not seated well; also, are we sure the vacuum hoses are connected/routed as they're supposed to be?


There is not a clamp or anything on the vacuum line going to the EGR valve. Maybe the old EGR vacuum fitting had a residue/buildup on it which helped "seal" the connection. Whereas the new one is clean and polished so there isn't a very good seal, when the engine/vacuum line is cold. due to the vacuum leak a few of you have mentioned, it takes the engine that few seconds to build proper vacuum in order to hold open egr diaphragm... (sorry, thinking out loud:D)
 

G Men 08

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Jun 15, 2010
Location
NY
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MK4 Golf 5 spd
Have you tried to disconnect the vacuum from the new valve to see if the idle goes back to normal? You can just plug the vacuum line temporarily.

It would be nice to watch the MAF numbers while idling to see if there is a fluctuation there...

500 miles per tank? How many gallons do you usually put in for a fill-up? I assume non-vented?

usually 11.5-12.5 gallons. Non vented (that I know of)

I lost MPG when I put the lift and snow tires on the ole girl:(
 

G Men 08

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Joined
Jun 15, 2010
Location
NY
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MK4 Golf 5 spd
80 Miles less on this tank of fuel?!! Same driving style and location as always.

Any other input? I am not finding anything out of the ordinary, the car drives fine.

Which values and blocks should I check VIA vagcom?
 

G Men 08

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Location
NY
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MK4 Golf 5 spd
Going through with vagcom now.

No codes.

At idle (903 rpm and holding steadily, warm engine)

Maf actual 490-500 mg/st (specified 255)

N18 solenoid 4.8%
 

G Men 08

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Jun 15, 2010
Location
NY
TDI
MK4 Golf 5 spd
Rotate the injector pump pulley, right?


I switched the egr duty cycle last night from factory setting of 32xxx to 33xxx. This morning I head out for work and the engine starts fine with no rpm division
 

G Men 08

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Jun 15, 2010
Location
NY
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MK4 Golf 5 spd
Adjusted the QA today. at warm engine idle it was floating between 1.2 and 1.4 mg/stk. Now it is around 4.5.
 

G Men 08

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Jun 15, 2010
Location
NY
TDI
MK4 Golf 5 spd
These engines are obviously loud. Looking for a vacuum/intake leak is nearly impossible (by listening).

Any advice or tricks on how to find where the potential leak is?
 

94cobra2615

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Jun 16, 2013
Location
ohio
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99 jetta tdi
I find vacuum leaks with a simple vacuum gauge with a nipple on the end to attach the vacuum lines to.

Unhook each line (individually....not all of them at once) with engine idling, and attach the gauge. You should see vacuum in the upper 20's. Doing one at a time like this you can isolate a vacuum problem.
 

G Men 08

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Location
NY
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MK4 Golf 5 spd
Alright, thanks cobra. Changed the oil and rotated the tires for winter, only 27psi. Oops. Bumped them up to 37.
 
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