[Yellowceta]

On the way to work this morning, I needed to beat some traffic when merging. I grabbed fourth from sixth and took it to around 5,500 rpms then shifted into fifth while clearing the slower traffic. As I clutched it, I felt a 'clunk' or hesitation. Once into fifth, there was no additional hesitation, but the SES light had come on and the general nature of the engine was much more rough than usual.

Most of the threads I have read on here with owners experiencing the rough idle and SES light, they said the car had entered 'limp mode'. I assumed this was the case and was able to pull off the road 1/4 mile further at my exit. I called up a friend who lived five miles down the road toward my final destination and he said come on over. He had all the tools I could dream of to fix anything automotive and then some. It took my about seven minutes to get there via farm to market roads and residential streets. However, by the time I did arrive, the SES light was off and the car was running smoother, much like normal.

The car has 58,000 miles on it and I have noticed over the past 15,000 miles or so that it would exhibit hesitation when at half to full WOT in the middle gears. This sensation was as if the boost never came on, then all of sudden hit. It was never smooth. The typical scenario would play out with me in 2nd gear ~4,500 rpms, then shifting into third and going WOT. The boost would be there in 2nd up to shifting, then when clutch was out and the transmission was in 3rd, the car would fall on its face with a little stuttering feeling like it was trying to claw its way back. By staying in it and letting the rpms climb, which I'm not sure how smoothly they did as I was always looking at other parts of the gauge cluster, eventually the boost came back. I would estimate around 4,500 rpms or so. This made passing prior to an onramp very interesting to say the least.

The only modifications I have done to this point have been Mad Dad mids, Akra w/wireless rear section, and Ohlin coilovers. I have no code reader nor know of anyone close by to drop by for a friendly scan. However, I might try to get into my dealership since my 60,000 mile checkup is right around the corner. I would like to be as prepared as possible in case they try to push off this issue as something they can't repeat. Therefore, I wanted to see if anyone had any ideas as to what could be causing this issue.

I haven't thoroughly checked my charge pipe, but I don't have a tune and drive the car like grandma usually. To be specific, I got almost 30,000 miles out of the OEM rears. My thought is the diverter valve failing. That would explain the hesitation where the diverter can't hold partial boost pressures, but then closes off after a little bit of time to be 'pushed' into place. I know that the diverter valve can be highly problematic on MkV GTi's since I have dealt with one before. However, I have no boost gauge to view boost pressure during the before mentioned scenario.

Anyone else have any ideas what might be causing this issue? If I can avoid going to the dealership because it's an easy DIY, that would be preferred. However, without better diagnostic tools, that may be unavoidable at this point.

I appreciate everyone's feedback in advance!!