Severe banging/misfiring

[RetroPug]

Recently I swapped the inlet manifold, pas pump and radiator.
I reused all sensors other than the cts and tps which I swapped for ones which worked fine on another car.
Now the car is hunting for idle, running poorly and misfiring very, very loudly at idle. It also revs very high on start up and settles if you touch the throttle
H
I can't figure out what is causing the problem. Disconnecting the battery helps a bit but then it gets worse again.

Any ideas?

I've have lots of responses on the gti6 forum but haven't gotten to the bottom of this yet:
http://www.306gti6.com/forum/showthread.php?id=160599

If anyone has any ideas I'd really appreciate it.

[cully]

I suspect ypu have an air leak.
With the car running spray some brake cleaner on the manafold joints and listen for the engine to change note

[toseland]

Carb cleaner is better for this than brake cleaner cully, alternatively give it a little blast with easy-start, the revs will rise somewhat with that

[RetroPug]

I will look for an air leak but that would surely just cause really high revs?
It is revving really high and then when I blip the throttle it goes normal (like a stuck ICV but replaced that), and then at idle it is as if someone is tapping the throttle erratically and it bangs and stutters very badly, then clears at higher revs.

[cully]

split resenator box or loose butterfly plate on its spindle

[RetroPug]

Resonator box was ok and I'm sure I didn't crack it when refitting, one of the bolts on the inside of the new TB holding the butterfly on looked a little rounded, will try swapping back to the old TB it ran fine with and see how that goes.

[ozonehostile]

Sounds throttle body related to me dude

[RetroPug]

Update:

Disconnecting one coilpack makes the banging/detonating go away, but not the erratic idle.
Disconnecting the others makes no difference. A fuel/ignition or double relay should be here tomorrow (thank you pug306).

Changed the throttle body back to the old one to see if the butterfly plate was bad and it made no difference.

I hope the fuel/ignition relay solves this, anything else it could be? Are the banging and erratic idle separate problems?

[RetroPug]

Tried another fuel/ignition relay, no difference.

However, I removed the inlet manifold for the 99th time to check injector cap locations and I noticed the brand new gasket has somehow got a huge hole in it on the cylinder that was banging and complaining:

Annoying that a brand new gasket has disintegrated like that...oh well. I just want the car to run now.

Also, my injector caps are all over the place because when I put them in I guess I didn't realise/forgot they could rotate independantly of the injectors:


If someone could tell me how the caps should be orientated that would be very much appreciated. Are they supposed to be horizontal (in this picture), or in line with the injectors at sort of 45ish degrees?

Thanks

[RetroPug]

I've been told injector caps don't matter.
This hole must be from taking the manifold off about 10 times, and the problem has always been there.

Also, when unplugging the coil for that cylinder, the engine still hunted all over the place and twitched the throttle so the hole can't be the only issue. :/

[RetroPug]

Update: Problem found....the mating surface of my inlet manifold was warped!!!!
There were a few other little air leaks but this was a major one!

Another manifold went on, runs better with no banging, just waiting on my 3rd new gasket in a row now to hopefully seal it once and for all.

[Ruan]

I'd possibly say that was from it backfiring out the inlet? Especially since it's warped, easy route for the gas to get through and blow out that little piece of gasket material.

[RetroPug]

Yep, it probably was. The banging was high up, not out the exhaust, so I suspect you are correct. The injectors weren't seated brilliantly either so now no leaks at ll around them.

No idea how the manifold warped....it came off my ph.2 which overheated and eventually had HGF, possibly the head got hot and warped the mating surface...but they were both warped so still sealed on that car...it was warped on the passenger-side cylinder which is typically where the HG fails from what I've read.

In any case, the mating surface wasn't straight when held up against a straight edge. Wish I'd let everything else on now and just done the PAS pump and rad with the bumper off...would have saved all this faffing!