Strange electrical fault on 172 cup

[Rkuk99]

Hi guys. Ok I'll start from the top.... Bought a 03 plate 172 cup couple months back as a project. Now when I got it the engine was clattering badly, cutting out etc. I stripped the timing covers off to find that the belt was actually slack, so got new belt, new dephaser and timed it all up using the correct tools. Clattering had gone but idled like a dog and was still cutting out. At this point I changed throttle body, throttle peddle, all 4 injectors, crank sensor, map sensor. Coil pack and there was new ngk plugs put in it but was still the same. After a lot of digging around discovered that both cams were 180 deg out. (Whoever done the belt before made a right c**t of it!) anyway timed it all up properly this time. Now idles much better, doesn't cut out attall and the mpgs up to 35.5. Now the only problem I'm left with which I'm at a dead end with is that in 3rd gear and 3rd gear only no matter what speed traveling at if the throttle pedal is held at the same position the car stutters. Put foot down and it clears. Only apparant in 3rd gear. Now that zig zag elec fault light is coming on now n then aswell, came on yesterday and brought the eml on with it, so read codes and came up with throttle position sensor and oxygen sensor bank 1 sensor 2. So cleared codes and changed the post cat sensor today. Took for a drive and still stuttering in 3rd and ziggy zaggy still making an appearance now and then. Eml hasn't come on again as yet tho. Now baring in mind all these parts that were replaced before, I.e throttle body etc were second hand used items. I'm at a dead end now with what the problem could be so looking for advice. My next steps firing it into renault but I'd rather not be ass raped lol. I sud also add that wen I originally collected the car and drove it home it was doing the same stuttering as it is now so surely it's something that I've not changed yet. I've also tried another set of ht leads but yet again no different. Any ideas guys?