Ok. Background story is that I was having some rough running issues on startup so I changed the plugs as they were due a refresh. I also had a duff coilpack so replaced that as well. But the car was still suffering when cold so I disconnected the sai plug and things did improve. But after a while I started having issues again which I isolated to the MAF which I replaced and things seemed better but after a week I am having slight issues again where it's been colds his last two days? I measured block 002 and it seeing 4gs so I know the MAF is ok, what I am wondering is what else runs when it's cold that can cause the vacuum to drop! I thought that just unplugging the sai pump was enough or does something else need to come out? I know for total removal I need a blanking plate which I will do eventually but what else could be causing cold running issues?

have you put it on a diagnostics to see if its throwing up any codes? maybe split pipes?

Ok I have done a bit more reading and I believe that there is a vacuum activation for the combi valve on the side of the block. Am I right in thinking that this activating when cold would cause it to run like a bag of 5h!te as the sai pump is unplugged?

If I disconnect relay j299 should that stop the vac activation of the combi valve and the sai pump from running?

I will get round to ripping them out eventually but just want it running right first.

The plot thickens!

Just went to have a look at disconnecting relay j299 next to 100 and 428 And I don't have j299?

I am foncused!

Edited 31 May, 201412 yr by karlbar2k

Ok further reading seems to indicate that the one labeled "100" is j299. Don't you just love how straightforward VAG cars are

I had rough running particularly when cold and misfire codes. Changed the maf and all seemed good for a bit, then it came back after a dsy or two. Turned out to be the vac pipe under the inlet manifold, it had a 3" split in it.

Likewise I also checked plugs and coilpacks. Could be worth a look. I managed to get my hand under there while the engine was running and could feel it blowing.

I am going to have to strip it down as I have already replaced all the pipe work in the last few years so it shouldn't be splitting already. I ran it with the 100/j299 relay pulled and it still runs like a bag of you know what. It still looks like something drawing vac when cold because as soon as it warms up it smooths out? If the j299 relay disables the sai and the combivalve then what else draws vacuum when the engine is cold? It draws 25 when running normally but when starting from cold it drops to 10-15 and runs like cr4p.

Edited 1 June, 201412 yr by karlbar2k

Do the engine simplification and fit the 3 resistors in place, if it is still the same then at least you know it's not that

I really should do the full simplification

Waiting to hear about a blanking plate.

Does anyone know what the cold start operation actually involves?

I know that after a couple of seconds the SAI is supposed to add unmetered air into the exhaust so it effectively lowers the back pressure to the engine, the ecu increases the fuel injection to allow unburnt fuel through so that it ignites in the exhaust there fore warming the cat quicker.

So unplugging the SAI pump stops the pumping of air, removing the relay (should) stop the combi valve opening but does it still flood the fuel through causing it to run like $h1te? Will gaping the plugs down a bit (0.03 on mk6 coil packs) help or can the cold start procedure be written out as part of stage 2?

Update:

Rough startup issue hasn't reappeared but I think that is mostly due to temperature being over 10c

Did Lose my boot/vac gauge the other day and could hear the hiss so fixed that with a new T piece and could still hear hissing. So further wiggling of pipes led to the small line from manifold to crank breather, which was les than 12 months old genuine vag part but inline check valve added and it was torn in two before the check valve..

Vac is back to 25 and boost is steady again so happy days are here again

Do the engine simplification and fit the 3 resistors in place, if it is still the same then at least you know it's not that

 

is there a thread on this? 

 

 

just got my VRS back from a mechanic who specialises  in VAG ...  he changed the PCV valve on the crank case... part number 06A-129-101-D

 

worked on mine..  may be some help to you.. 

I stripped and cleaned the PCV on mine and then put extra check valve in the line. the one that just got replaced again

Cold start the other morning (cold enough) and the roughness is still there.. Not as bad as before fixing the vac/boost leak though.. Smells rich when first running rough so I guess the cold start program for the cat warm up puts a load of fuel through and the air through the SAI to burn in the cat. Really need to get it stripped out and map changed to remove that feature.