Sporadic, Occasional stumble (misfire) on startup

[joshuawheat]

I have an 08 A4 Avant S-Line that has this phantom issue I have been tracking for a few months. I have searched and cannot seem to find anything conclusive to what the issue may be. I have this issue where occasionally, and mainly on warm startups (drive car and park, then 30 min to an hour or so later I come out and restart the car and it starts, but its like it stumbles (slightly rough idle) for a second or so and then the idle smooths out and sits at 800 or so and all is good. I have replaced so far;

Cam chain and tensioner, cam follower (old follower looked brand new)
Rev d diverter valve
n75 valve
fuel filter
LPFP with VDO unit (duty cycle is 54-55% at idle fully warm via vag com)
checked spark plugs (had some carbon deposits, cleaned and re-gapped to .030, Coils look older and have brown on the metal sheathing (possibly bad??)
PCV valve (newest revision) and PCV hose to intake
unplugged maf and it made the idle rough

I have no codes, nor does it throw codes while it is happening. I have replaced all of these things less than 1000 miles ago. I am Gonzo Stage 2 tuned and it pulls like a freight train and runs beautifully. This seems to be the only issue. Changing the fuel pump did help a little, as in the stumble isn't as pronounced as it was before the pump change. I am stumped because I get no codes and it runs beautifully other than that. Any help is appreciated

Pic of said car..

[joshuawheat]

I guess I'll go ahead and update. I replaced all 4 coils with denso replacements and bkr7eix spark plugs gapped at .030 and I started it only once since the install. The startup was vastly improved with no stuttering or anything odd. I will keep updating on here when I get a chance to drive the car more regularly. If anyone has any input, please feel free to chime in, as I still don't know if this is the fix as of yet.

[pezgoon]

In for answer

I was getting this issue and just pegged it to needing a carbon cleaning, I haven’t done it but after I installed jhm stage 1 it stopped doing it???

I’m curious what the actual solution ends up being for it, hopefully you figure it out, it’s interesting because the things I was thinking it could be didn’t seem to help you (maf, n75, lpfp, pcv)


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[Sylvania A4]

^^ must be nice, mine has done it ever since going from REVO stg 2 to JHM.

[pezgoon]

^^ must be nice, mine has done it ever since going from REVO stg 2 to JHM.

Oh no I have a new issue after doing the tune, now it stumbles/cuts out at low rpms and extremely light load. Not even the faintest idea of where to start looking for that...

I’d rather have the cold start issue back, too late now though

I’m just really curious as to why it would’ve been fixed by tuning lol that makes no sense to me??


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[funkypterodacty]

You can try cleaning the MAF, see if that does anything.

[pezgoon]

You can try cleaning the MAF, see if that does anything.

As of note if you’re speaking to me I’ve cleaned it I believe twice since I got the car and it didn’t help, now that I’m tuned I can’t try unplugging it and starting it since now I don’t have the issue anymore :( (The cold start issue)


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[joshuawheat]

I will hopefully have an answer by the end of the weekend. I will be driving the car from tomorrow evening through Monday. I may attempt replacing the N80 valve for sh!%s and giggles to see if that helps as well. I did forget to mention that the head has been replaced on the car VIA Audi.

[joshuawheat]

As of note if you’re speaking to me I’ve cleaned it I believe twice since I got the car and it didn’t help, now that I’m tuned I can’t try unplugging it and starting it since now I don’t have the issue anymore :( (The cold start issue)


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just to clarify, My starting seems mainly to be warm starts after it sits for 30 min to an hour or 2

[pezgoon]

just to clarify, My starting seems mainly to be warm starts after it sits for 30 min to an hour or 2

Ahh that does make an issue, mine was the opposite, only stone cold and existed during cold weather only, if the engine was warm at all it wouldn’t do it and summer it didn’t do it


Out of curiosity, ever pulled out/changed your CPS? Maybe pull it out and clean it off

When I had a Saab hard starting issues when warm was caused by a bad cps

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[joshuawheat]

Ahh that does make an issue, mine was the opposite, only stone cold and existed during cold weather only, if the engine was warm at all it wouldn’t do it and summer it didn’t do it


Out of curiosity, ever pulled out/changed your CPS? Maybe pull it out and clean it off

When I had a Saab hard starting issues when warm was caused by a bad cps

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I did ponder that thought. I have researched the CPS and that is a viable point. My 06 Saab 9-3 aero had that issue and the cps was the culprit. but usually the cps will cause it to die immediately after starting and can cause random shut offs. It is a relatively cheap part and i may replace it as well.

[pezgoon]

I did ponder that thought. I have researched the CPS and that is a viable point. My 06 Saab 9-3 aero had that issue and the cps was the culprit. but usually the cps will cause it to die immediately after starting and can cause random shut offs. It is a relatively cheap part and i may replace it as well.

Mine was a 2001 Saab 9-5, I only had issues with starting once hot. I bandaided it by pouring water on it to cool it down instead of just replacing it haha


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[nizmosx]

when i had those issues, they started getting progressively worse. i swapped spark plugs and coil packs and it persisted. Turned out to be clogged injector.

i have since replaced them and have NOT had the issue.

[pezgoon]

when i had those issues, they started getting progressively worse. i swapped spark plugs and coil packs and it persisted. Turned out to be clogged injector.

i have since replaced them and have NOT had the issue.

Even cold starting?


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[joshuawheat]

when i had those issues, they started getting progressively worse. i swapped spark plugs and coil packs and it persisted. Turned out to be clogged injector.

i have since replaced them and have NOT had the issue.

clogged injector would have more tell-tale signs, wouldn't it? ie throw codes? misfire under WOT, pulling timing, very high duty cycle? I monitor my fuel system with OBD eleven (vag com) and all of my fueling seems to be in good order. I will definitely keep this in mind, though

[pezgoon]

^^ must be nice, mine has done it ever since going from REVO stg 2 to JHM.

clogged injector would have more tell-tale signs, wouldn't it? ie throw codes? misfire under WOT, pulling timing, very high duty cycle? I monitor my fuel system with OBD eleven (vag com) and all of my fueling seems to be in good order. I will definitely keep this in mind, though

Just out of random curiosity, try giving the car alittle throttle while cranking it. For me it was literally the only way I could get the car to start during this past winter (again confuses me but I think it’s point to carbon cleaning needed for me)

Just curious if it helps others too or if it was specific to mine

And yes it does work


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[EvolutionArmory]

^^ must be nice, mine has done it ever since going from REVO stg 2 to JHM.

Call Dru about this. He recently cured my cold start issue with a new revision for my ECU box code. Do you have an early B7 or late?

[pezgoon]

Call Dru about this. He recently cured my cold start issue with a new revision for my ECU box code. Do you have an early B7 or late?

Early here but I want more info lol


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[EvolutionArmory]

Just out of random curiosity, try giving the car alittle throttle while cranking it. For me it was literally the only way I could get the car to start during this past winter (again confuses me but I think it’s point to carbon cleaning needed for me)

Just curious if it helps others too or if it was specific to mine

And yes it does work


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A drive by wire car, for the most part, controls everything needed to start your car electronically. I really doubt “pumping the gas” does anything on a modern fuel injected car until it’s at idle.

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Early here but I want more info lol


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Call and speak to Dru.

[pezgoon]

A drive by wire car, for the most part, controls everything needed to start your car electronically. I really doubt “pumping the gas” does anything on a modern fuel injected car until it’s at idle.

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Call and speak to Dru.

I didn’t say pump it, you just give it some throttle and hold it.

You can deny it all you want but as I said, it was literally the only way my car would start all winter no matter how cold it is. If you haven’t noticed the car does not shut off the systems while cranking and I’m guessing this means as soon as you start cranking the throttle becomes active, alls I know is it worked and I’m so glad I had found it as I would have to crank the car for a good 30 seconds+ to get it to start before I found it, afterwards it started immediately all the time every time no matter the temp

Good to know thanks


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[Sylvania A4]

Call Dru about this. He recently cured my cold start issue with a new revision for my ECU box code. Do you have an early B7 or late?

Late.


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[joshuawheat]

I didn’t say pump it, you just give it some throttle and hold it.

You can deny it all you want but as I said, it was literally the only way my car would start all winter no matter how cold it is. If you haven’t noticed the car does not shut off the systems while cranking and I’m guessing this means as soon as you start cranking the throttle becomes active, alls I know is it worked and I’m so glad I had found it as I would have to crank the car for a good 30 seconds+ to get it to start before I found it, afterwards it started immediately all the time every time no matter the temp

Good to know thanks


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I will try to see if it helps and get back with the info. Mine still starts easily, as in on the first crank, it's just like the idle stumbles (still holds around 800 rpm) a little for a second or so and then smooths out. I am leaning towards either the ignition components (after further inspection of the spark plugs, the electrode was very worn on all 4. The coils were also brown and rusty looking around the sheathing) I will still update this weekend to see if this was the cure for my particular issue. Anyone with similar situations feel free to chime in with any potential knowledge you may have. I'd like to be able to help as many people as I can.

[pezgoon]

I will try to see if it helps and get back with the info. Mine still starts easily, as in on the first crank, it's just like the idle stumbles (still holds around 800 rpm) a little for a second or so and then smooths out. I am leaning towards either the ignition components (after further inspection of the spark plugs, the electrode was very worn on all 4. The coils were also brown and rusty looking around the sheathing) I will still update this weekend to see if this was the cure for my particular issue. Anyone with similar situations feel free to chime in with any potential knowledge you may have. I'd like to be able to help as many people as I can.

Ah okay I see what you mean, I was thinking it was more like what I was having which was once it finally tried starting it was running on two or three cylinders (so literally misfiring on the other two) and would either stall back out or eventually get going




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[joshuawheat]

Alright, as promised, I have an update. I got it to do it's business once today. Started up just like normal, after driving for a while and letting it sit for an hour. And it sat around 850-900rpm instead of going up to 1200 (secondary air pump on) for a second then jumped up to 1200 after a second or 2 and all was well. So, back to square 1. I am now leaning towards coolant temp sensor.

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[marakalastic]

Just out of random curiosity, try giving the car alittle throttle while cranking it. For me it was literally the only way I could get the car to start during this past winter (again confuses me but I think it’s point to carbon cleaning needed for me)

Just curious if it helps others too or if it was specific to mine

And yes it does work


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Funnily enough, this is the only way I can reliably start my car since I owned it 2 years ago... If I don't keep the pedal pushed down about an inch (along with the clutch) when I go to start it, it will most likely struggle to start and some times fail to start at all. Turning the key back and then trying to start it again, the car will crank and start no problem. With the pedal pushed down about an inch, it will start the first try no matter what but will struggle to varying degrees.

Any ideas as to why? I've got a 3.2

[pezgoon]

Funnily enough, this is the only way I can reliably start my car since I owned it 2 years ago... If I don't keep the pedal pushed down about an inch (along with the clutch) when I go to start it, it will most likely struggle to start and some times fail to start at all. Turning the key back and then trying to start it again, the car will crank and start no problem. With the pedal pushed down about an inch, it will start the first try no matter what but will struggle to varying degrees.

Any ideas as to why? I've got a 3.2

Thank you! I knew I couldn’t be the only one.

For me even returning the key and trying again wouldn’t help. I am so desperate to know what this could be indicating especially because I no longer need to do it since installing jhm stage 1 and I have no idea how that is possible!! With how difficult my car was to start I don’t understand how installing the tune could’ve fixed it and no one even seems to want to shoot in the dark about it. I made a thread and didn’t get a single response in like two weeks so I gave up.


And idea of the state of your carbon buildup??


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[EvolutionArmory]

Thank you! I knew I couldn’t be the only one.

For me even returning the key and trying again wouldn’t help. I am so desperate to know what this could be indicating especially because I no longer need to do it since installing jhm stage 1 and I have no idea how that is possible!! With how difficult my car was to start I don’t understand how installing the tune could’ve fixed it and no one even seems to want to shoot in the dark about it. I made a thread and didn’t get a single response in like two weeks so I gave up.


And idea of the state of your carbon buildup??


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With your car being especially hard to even start during winter, did you try replacing the CTS? A bad CTS can absolutely make a car hard to start. If it thinks the coolant temp is colder than it really is it will dump a ton of fuel trying to get it to start, basically flooding the motor.

[pezgoon]

With your car being especially hard to even start during winter, did you try replacing the CTS? A bad CTS can absolutely make a car hard to start. If it thinks the coolant temp is colder than it really is it will dump a ton of fuel trying to get it to start, basically flooding the motor.

I did not but you could be onto something there! And that could be why opening the throttle could help because of the extra airflow, anyway that I can test it without just replacing it? I have a long list of things to replace right now and would prefer not to add more if unecassary haha


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[EvolutionArmory]

I did not but you could be onto something there! And that could be why opening the throttle could help because of the extra airflow, anyway that I can test it without just replacing it? I have a long list of things to replace right now and would prefer not to add more if unecassary haha


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You would have to know what the internal resistance of the part is suppose to be and then compare what your part reads with a multimeter.

[marakalastic]

Thank you! I knew I couldn’t be the only one.

For me even returning the key and trying again wouldn’t help. I am so desperate to know what this could be indicating especially because I no longer need to do it since installing jhm stage 1 and I have no idea how that is possible!! With how difficult my car was to start I don’t understand how installing the tune could’ve fixed it and no one even seems to want to shoot in the dark about it. I made a thread and didn’t get a single response in like two weeks so I gave up.


And idea of the state of your carbon buildup??


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I don't have any idea at all, I didn't get any service records prior to my ownership unfortunately... I don't get any misfires (used to) anymore but I do get codes for both my banks running rich (P0172 and P0175) that last a couple of days. The codes will stay off for a couple of days and then come back for a couple of days and repeat. not sure if that's related, haven't figured out what my issue could be yet.

The coolant temperature sensor sounds like it's definitely a possible solution for your description but my car doesn't really struggle harder than usual in the winter (I'm in Vancouver BC) than in the summer, at least not to the extent that I remember it. I'll definitely still look into that as a solution though as I have no alternatives!

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[pezgoon]

You would have to know what the internal resistance of the part is suppose to be and then compare what your part reads with a multimeter.

Excellent idea! I’m gonna dig around the fsm I’ve got and see if it has any specs to diagnose it (I believe it might as it has specs for a lot of sensors in there) hopefully this could help send me in the right direction


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[EvolutionArmory]

Excellent idea! I’m gonna dig around the fsm I’ve got and see if it has any specs to diagnose it (I believe it might as it has specs for a lot of sensors in there) hopefully this could help send me in the right direction


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That was always the first step in any test plan I ever followed at the dealer when diagnosing an electrical part. Measure actual resistance to specified. It’s much easier when you have all of that info available at the touch of a button. I miss having an ELSA log in bad.

[Theiceman]

Alright, as promised, I have an update. I got it to do it's business once today. Started up just like normal, after driving for a while and letting it sit for an hour. And it sat around 850-900rpm instead of going up to 1200 (secondary air pump on) for a second then jumped up to 1200 after a second or 2 and all was well. So, back to square 1. I am now leaning towards coolant temp sensor.

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secondary air pump ?? I didnt realize these cars even had one !!!

[Theiceman]

at first glance it seems to me you are bleeding off fuel pressure.
When its warm you have no cold start assist so it is depending on system fuel pressure to get you started. If you are bleeding off fuel pressure you will get your symptoms when you try to do a warm start after sitting.

[EvolutionArmory]

secondary air pump ?? I didnt realize these cars even had one !!!

They don’t. Pre cat warm up is done with the intake flap control system.

[EvolutionArmory]

at first glance it seems to me you are bleeding off fuel pressure.
When its warm you have no cold start assist so it is depending on system fuel pressure to get you started. If you are bleeding off fuel pressure you will get your symptoms when you try to do a warm start after sitting.

That’s not necessarily true. When it’s below 40 degrees you don’t have pre cat warm up because it’s better for the motor to rev lower when the oil is thickest, when it’s cold. Above 40 degrees the pre cat warm up will activate when you first start the car.

[Theiceman]

That’s not necessarily true. When it’s below 40 degrees you don’t have pre cat warm up because it’s better for the motor to rev lower when the oil is thickest, when it’s cold. Above 40 degrees the pre cat warm up will activate when you first start the car.

I'm not talking about cat warm ups a, I'm talking about cold start enrichment, triggered by coolant temp sensor.

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They don’t. Pre cat warm up is done with the intake flap control system.

I know lol , but I kinda wanted him to get there on his own ;)

[joshuawheat]

I'm not talking about cat warm ups a, I'm talking about cold start enrichment, triggered by coolant temp sensor.

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I know lol , but I kinda wanted him to get there on his own ;)

All are great answers, as I had no idea about the non existent secondary air system. I will log my fuel pressures. If I remember correctly, I have previously and they seem fine. the pump primes as it should, also. I ordered my CPS and CTS today and I should have by Wednesday. When installed, I will report back with my findings.

[Theiceman]

sounds good ,,, as far as logging fuel pressure goes, can you log it while car is static ? ie see how much it leaks down over time while sitting ? that would be helpful even if not related to your issue.

[EvolutionArmory]

I'm not talking about cat warm ups a, I'm talking about cold start enrichment, triggered by coolant temp sensor.

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I know lol , but I kinda wanted him to get there on his own ;)

Yes, but cold start fuel enrichment usually happens in conjunction with secondary air pumps, which we don’t have. In essence, you and I are talking about the same thing. The CTS tells the car to add fuel and the SAI adds more air. We don’t have a SAI so it’s all done with the IRC.

I would definitely recommend starting with a CTS and if that doesn’t do it, try to run IRC basic settings. If the IRC motor has failed, it might not throw a code for it. Running the basic settings for it and it failing will probably cause it to throw the code for it and we will know if that’s the direction we need to go in.