9N3 Polo GTI: CEL + P1176 + Flatspot

[pog]

Hi Fellas,

Before I go on, I will say I have done all the research possible on my own regarding this thread. But to confirm my understanding from various threads, posts, reviews etc, I will proceed with my situation.

Car: Polo GTI 9N3 (1.8T)
Engine Mods: Seat PD160, 3" Custom HFC + Downpipe with o2 spacer, APR Tune, APR R1 DV

Since installing the downpipe, I've recieved the infamous P1176 code. And just more recently, I'm now getting a flat spot at 4,000rpm. Based on Ross Tech, P1176 relates to either an intake leak and/or o2 sensors (Ross Tech) and a flat spot can relate to various things such as "MAF sensor, spark plugs, o2 sensor". Ever since getting it, my understanding is that despite having a HFC, the P1176 in some circumstances will display, but the code shouldn't affect performance. Whilst it doesn't affect performance too great, it's noticeable that there is some power loss.

Independently, I have done a smoke test at the mechanic to scan for any intake leaks but came up without any issues. Exhaust bolts and flanges were secure and the o2 angled spacer was on correctly. As a second test, I tested the post cat o2 sensor via VAGCOM some months ago on my friends rear o2 sensor. The voltage was roughly the same as mine + or - .05. So that to me eliminated the need for a new o2 sensor as the sensor was behaving in a "normal" way.

I haven't checked the spark plugs, but when I do, I will be looking for a lean result. If so, I will be replacing them. I'm referring to lean, mainly because of the flat spot. Then next, I'll look at the MAF sensor. I will say though, when I unplugged the MAF and drove around for a while, the flat spot was still evident. So I figured, it has nothing to do with the MAF then and possibly something else. Is this a fair assumption?

I'm thinking it may be the spark plugs coupled with the rear o2 sensor. And lastly, to end my rant I've switched the to the stock MAP, and when I WOT, there is no hesitation. Could it simply be because there's less power? Can someone please validate what I've just said or add to it.

Thanks