Help with 2007 GTI Idle Issues


New member
Edmonton, AB
2007 MK5 GTI
Hey guys, was wondering if anyone had an idea of what could be going on with my 2007 MK5 GTI DSG. A couple weeks ago I started noticing some engine issues - a rough idle with rpm drops, random idle surges up to 1500 rpm and a slight hissing noise when I turned off the engine. The CEL also came on soon after and gave me two codes: P0171 (System Too Lean Bank 1) and P0507 (Idle Control System RPM Higher Than Expected).

After doing some searching on here it seemed like a failing PCV valve would be most likely; the problem was I just had it replaced ~3 months ago along with some other repairs due to a previous CEL (P0171 as well) and it seems highly unlikely there would be an issue with it again so soon. I also had the diverter valve and thermostat replaced at the same time.

To make things more complicated, ~4 days after this all started (and right before I was about to take it in to investigate) everything decided to resolve on its own - all the symptoms disappeared and the CEL turned off. The car continued to run smooth for around a week and then yesterday I started to notice the same issues coming back and the CEL came on again. It's not happening continuously like it did last time, but every time I shift into park it'll begin to climb to ~1500 rpm and then if I put it back into drive it'll drop to ~750 rpm and idle rough for around 5-10 sec, fluctuating between 500-750 rpm. Same thing happens if I shift into neutral while stopped: shift to N -> rpms climb to ~1500 -> shift back to D -> immediately drops to ~750 and idles rough/fluctuates for a bit.

The only other odd thing that I think I've noticed (honestly not sure if I'm imagining it or not, but it just feels off) is that the car sometimes seems like it maintains its speed at around 20 kph when my foot is off the gas.

Any help would be much appreciated! Side note, although I enjoy reading up online and trying to figure out what's going on I'm not the most mechanically inclined myself besides simple stuff like oil changes, brake pads, small electrical issues and the like. So I apologize in advance if I have no idea what someone is talking about haha.


2007 MKV GTI
This is typically caused by a leak in the air inlet system between the MAF sensor and the port inlets...or leaks in the tubing off of the intake manifold or brake booster. You can disconnect the MAF wires...does it suddenly idle smoother and run smoother where you've noticed it a bit lumpy? If usually confirms the MAF is bad or that there is a leak between the two points mentioned.

If may be a number of things. From clogged catalyst, failing B1S1 O2 sensor, improper crankcase ventilation, inlet air restriction or fuel delivery. Begin with the MAF check and report the findings.