Weird short rough idle at startup with coldstarts

[Ebird13]

So recently just replaced the cylinder head on an 07 A4 BWT engine and was running fine for a few weeks. Now something weird is going on...when I start it up after letting it sit for a few hours, for the first couple seconds with will seem like it’s missing and then after a few seconds and acts normal again. New LPFP, HPFP, and fuel filter within last 1500 miles. New plugs as well. Perhaps coil packs on their way out? If you start the car up after it was just running it does not do this. Anyone experience this? No codes coming through on My vagcom tool either

[hellabrendan]

my car does the same exact thing, my brothers b7 does it too (but not as badly) and even my dads cc with the fsi does it. i have new plugs, new-ish red coils, new cams, new timing chain, new belt, cleaned the maf, new silicone intake charge pipe, new pcv valve, and still does it. thinking it might be normal.

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my dads tsi * sorry

[texadelphia]

Have you monitored the misfire count through vagcom? It might be misfiring but not enough to throw any codes. I had a similar problem with my car for a while. Turned out to be bad injectors.

[Ebird13]

Have you monitored the misfire count through vagcom? It might be misfiring but not enough to throw any codes. I had a similar problem with my car for a while. Turned out to be bad injectors.

I’ll try this this weekend and report...the car was burning a quart every 300 miles before head replacement (bad guides and seals) so it would not surprise me with being direct injection if I should’ve just went ahead and replaced injectors...are you assuming then it’s injector leakdown in the cylinder?

[texadelphia]

I’ll try this this weekend and report...the car was burning a quart every 300 miles before head replacement (bad guides and seals) so it would not surprise me with being direct injection if I should’ve just went ahead and replaced injectors...are you assuming then it’s injector leakdown in the cylinder?

Yeah, my injectors were leaking when it was sitting.

[Jeevan]

Before wasting anymore money. Do a leakdown test


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[Ebird13]

Before wasting anymore money. Do a leakdown test


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Can this test be completed via the logs in the measuring blocks or should it be done through a manual gauge on fuel rail?

[EvolutionArmory]

Can this test be completed via the logs in the measuring blocks or should it be done through a manual gauge on fuel rail?

He’s talking about a leak down test of the cylinder head. Was the one you bought used? Leak down test will tell you if your valves are sealing.

Verify the head is good and then go after the injectors as a potential cause.

Have VCDS monitoring misfires when when it’s acting up. Block 015 and 016. If it’s only misfiring on one cylinder, then you’ll know which to target. If Leakdown is bad on that cylinder, you’ll know it’s the head. If not, it’s probably an injector.

Then pull that plug and see if it smells like fuel or is wet. If it’s wet, your injector is leaking.

Another thing I would do is do an intake runner motor adaptation in basic settings and see if it passes. It might be failing but not throwing a code. Doing its basic settings test might force it to fail and throw a code for it. Or it will pass and you’ll know the tumble flap system is working right and you can cross it off the list.

[Ebird13]

He’s talking about a leak down test of the cylinder head. Was the one you bought used? Leak down test will tell you if your valves are sealing.

Verify the head is good and then go after the injectors as a potential cause.

Have VCDS monitoring misfires when when it’s acting up. Block 015 and 016. If it’s only misfiring on one cylinder, then you’ll know which to target. If Leakdown is bad on that cylinder, you’ll know it’s the head. If not, it’s probably an injector.

Then pull that plug and see if it smells like fuel or is wet. If it’s wet, your injector is leaking.

Another thing I would do is do an intake runner motor adaptation in basic settings and see if it passes. It might be failing but not throwing a code. Doing its basic settings test might force it to fail and throw a code for it. Or it will pass and you’ll know the tumble flap system is working right and you can cross it off the list.

So the head is used but I had it checked over with penetrant to look for cracks and stuff and the car was never overheated just had a valve issue which had to pull the head for. Compression is ~200 on all cylinders, and after a couple seconds usually runs great. So I checked fuel pressure on the rail yesterday and at idle it sits at 750 psi and after 60 secs of turning the car off it lost 90 psi. I let it sit overnight and it was at 100 psi this morning. The car didn’t stumble though this morning like it has before. Anyways, I’m assuming this is pointing to either a leaking injector because I don’t smell fuel anywhere. I’ll pull the plugs and see what I find. Thank you.

[EvolutionArmory]

Leaky injector doesn’t mean leaking fuel out of a seal so you’ll smell it.

A leaky injector in this instance means failing internally, not atomizing correctly, or not opening and closing correctly, etc.

Leaking into the combustion chamber, not the engine bay.

It sounds like that is what you meant but I just wanted to make sure. Not smelling fuel would mean any pressure loss is going into your cylinder. If your plug is wet, this would help confirm it.

You could pull your dipstick and see if it smells like gas too. You might not smell it unless the injector leak is pretty bad though. If it’s real bad that fuel is gonna leak past the piston rings and contaminate your oil.

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[Ebird13]

Leaky injector doesn’t mean leaking fuel out of a seal so you’ll smell it.

A leaky injector in this instance means failing internally, not atomizing correctly, or not opening and closing correctly, etc.

Leaking into the combustion chamber, not the engine bay.

It sounds like that is what you meant but I just wanted to make sure. Not smelling fuel would mean any pressure loss is going into your cylinder. If your plug is wet, this would help confirm it.

You could pull your dipstick and see if it smells like gas too. You might not smell it unless the injector leak is pretty bad though. If it’s real bad that fuel is gonna leak past the piston rings and contaminate your oil.

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Yeah that’s what I meant, can’t smell it so assuming it’s leaking into cylinders. I’m gonna pull plugs this afternoon. The car was burning oil really bad before hand and I didn’t refresh the injectors before putting it all back together, probably has something to do with it since it’s direct injection. LPFP duty looks great on the measuring blocks, and the HPFP was just replaced so I would doubt it’s the check valve. I’ll confirm by pulling the plugs but right now looking like a leaking injector.

[EvolutionArmory]

Do a leak down test to confirm it’s not the head. Once that’s ruled out, going after injectors is a good idea.

And do the intake runner motor adaptation just for the hell of it.

[Ebird13]

Do a leak down test to confirm it’s not the head. Once that’s ruled out, going after injectors is a good idea.

And do the intake runner motor adaptation just for the hell of it.

I don’t have the equipment to do the leak down test yet so that’s going to have to wait a little bit but I was able to use the misfire counter and look for what cylinder it was missing on (cylinder 2). Moved coil from 1 to 2 to see if it followed, misfire stayed on 2. Pulled plug smelled like straight gas and was slightly wet.

I’ll do the runner adaption just for the hell of it as well, but I think I found my culprit.

[EvolutionArmory]

If you saw 2 misfire and pulled plug 2 and it stinks, that about nails the diag. A new injector would be a safe bet.

[EvolutionArmory]

You’ll also want to do an oil and filter change when you get the injector or injectors replaced. If you smell gas on your plug, your oil is most likely contaminated from raw fuel washing past the piston rings.

Don’t drive the car until it’s fixed.

[Ebird13]

You’ll also want to do an oil and filter change when you get the injector or injectors replaced. If you smell gas on your plug, your oil is most likely contaminated from raw fuel washing past the piston rings.

Don’t drive the car until it’s fixed.

I am assuming if one of the injectors went, probably best to go ahead and replace them all when I am in there...although I'm not happy with the prices I've seen on FCP! haha I guess I am just irritated because I spent so much money with getting the head all rebuilt and a bottom end and transmission last year. I want to just stay stock sizing for now, any leads on decent injector prices? If thats normal pricing, I Guess it is what it is, but just weird same kit for the B8 is 229 for all 4, but for the b7 its 400+.

[Charles.waite]

What is your resting battery voltage? A really low resting voltage could result in some cold start roughness until the alternator is able to float the voltage back up to a normal level. I wouldn't rush out and buy a new battery, but if your resting voltage is much under 12 and it drops even more when you turn the accessories on, then you might have a dying battery.

[Ebird13]

What is your resting battery voltage? A really low resting voltage could result in some cold start roughness until the alternator is able to float the voltage back up to a normal level. I wouldn't rush out and buy a new battery, but if your resting voltage is much under 12 and it drops even more when you turn the accessories on, then you might have a dying battery.

Battery was new as of a couple weeks ago, seems like diagnosis is a leaking injector. Will report back once replaced

[Charles.waite]

Battery was new as of a couple weeks ago, seems like diagnosis is a leaking injector. Will report back once replaced

Cool. Figured I’d throw out the battery idea just in case.

[texadelphia]

I am assuming if one of the injectors went, probably best to go ahead and replace them all when I am in there...although I'm not happy with the prices I've seen on FCP! haha I guess I am just irritated because I spent so much money with getting the head all rebuilt and a bottom end and transmission last year. I want to just stay stock sizing for now, any leads on decent injector prices? If thats normal pricing, I Guess it is what it is, but just weird same kit for the B8 is 229 for all 4, but for the b7 its 400+.

FWIW I started with one bad injector and just replaced the one. Then a few months later another went bad so I ended up replacing the remaining 3...replacing them all might be the right choice unless you really like wrenching.

[Ebird13]

FWIW I started with one bad injector and just replaced the one. Then a few months later another went bad so I ended up replacing the remaining 3...replacing them all might be the right choice unless you really like wrenching.

Yeah after recently doing the motor, trans, and head twice I’m at about my wrenching limits!

[esandes]

How old is the PCV?

[Jeevan]

How old is the PCV?

Every problem in the world is not about PCV and coil packs.


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[Ebird13]

Every problem in the world is not about PCV and coil packs.


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Haha I run an 034 catch can system and have ran it for around 10k miles no issues. I moved packs around and issue stayed in same cylinder. Like I have said, definitely an injector..:just trying to price a good set to throw in now

[texadelphia]

Haha I run an 034 catch can system and have ran it for around 10k miles no issues. I moved packs around and issue stayed in same cylinder. Like I have said, definitely an injector..:just trying to price a good set to throw in now

Have you considered sending your current injectors out to be cleaned, rebuilt, and flowed? I briefly looked into it but I didn't want to wait a week for them to get back to me.

[EvolutionArmory]

Every problem in the world is not about PCV and coil packs.


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When your wheel of diagnosis only has 2 sections or your diagnostic dice only have 2 sides, Esandes 😀

[Charles.waite]

When your wheel of diagnosis only has 2 sections or your diagnostic dice only have 2 sides, Esandes

Hey at least he’s not suggesting it’s bad gas or something equally nonsense.