Car's cold start is nonexistent. Help

[Shotter]

The car is Audi A4 B6 BFB 2004 sedan, the issues are that when i start the car a little bit below 0 celsius it will start but then the rpm will drop to 0 and it will go off after starting it a few times and pressing the gas pedal or otherwise getting engine heat up will it start running properly, but when braking it will run really rough again, it wasn't a issue in summer or when the outside temp was +5 but it still ran rough then when starting and there were sudden moments of it running rough when trying to speed up. but they will all go away when the motor is at 90 celsius, there's also a engine light and if we remove fault codes or take the battery off and the fault codes are cleared the car will not run at all if its not at 90celsius. i've also noticed poor fuel economy. also sometimes when braking from around 60kmh to 20kmh the car will try to stall and sometimes just shut off even with the clutch pressed. Also when putting key to ignite and priming fuel, now that its cold there's some type of squeal noise, didn't notice this before in summer.

We have changed the o2 sensor, thermostat, MAF, and we will be changing fuel filter next week, the service manual says that the fuel pump has been changed around 6-7 years ago so around 20k kilometers ago, the car has been sitting for 6 years so i assume the fuel pump should still be just as good as it was when it was changed. Fault codes are 18010 power supply terminal 30 p1602 -002- voltage too low - intermittent. and 17536 - fuel trim; bank 1 (mult) p1128 -001 - system too lean -mil on. Hoping to get some some help on what parts we could still change or what else we could do to get it running properly in winter too. the spark plugs are also quite new, we have checked for vacuum leaks multiple times with motor starter spray, around the fuel injectors, spark plugs, pretty much anything that can be seen and have noticed no difference in the rpm's while doing that, ofc if there's some really hidden spots it would be great to know so we can check there too, we have only checked them from the motor and the area around it.


(edit) The car does start properly but it doesn't stay on. it needs to be heated beforehand, after its heated enough to stay on and you go on to drive there's a lot of misfires, like it really struggles to stay on when driving on first gear but if i accelerate on first gear to around 3k rpm all the misfires disappear same thing with second gear at 3k rpm all misfires disappear and the car starts working like a dream until it drops below 3k rpm again

[grayjay]

A bad temperature sensor to the ECU can cause poor cold starting. This is one of the 2 sensors on back of the head, other is just for the instrument cluster. Make sure that the sensor is working well. Low voltage will also cause other issues, check that battery is fully charged and alternator is working.

[Shotter]

A bad temperature sensor to the ECU can cause poor cold starting. This is one of the 2 sensors on back of the head, other is just for the instrument cluster. Make sure that the sensor is working well. Low voltage will also cause other issues, check that battery is fully charged and alternator is working.

Thanks, will change that temp if fuel filter doesn't do anything, seems easy enough, also the battery is fine and only rust can be seen on alternator but it seems to work fine

[Shotter]

sorry for late reply but yeah we changed the temperature sensor and fuel filter but nothing changed there's a high pitched noise coming from both rear wheels, its louder on the passenger side tho, so could it be the fuel pump after all? its only there when the car is idling, we also tried different battery but that didn't do anything either

[codemode]

Are there any misfires?
Can you hear the secondary air pump running?

How bad is the chain rattle and are you loosing any coolant?

[Mike Tries]

The fuel pump is under the rear seat. Pop the rear seat cushion off and see how loud it gets. Even with the seat cushion off, the pump shouldn't be what I would describe as "loud". It should be under a little access panel on the passenger side.

[Shotter]

Coolant is leaking but only when the engine is hot also yeah there's engine misfires, i'm not sure of chain rattle or air pump sound yet ill record it in a bit since i don't really know how the engine should sound.

[Shotter]

can't hear the high pitched noise when inside of the car but when turning the key on top but not starting the engine, the fuel pump does make a loud sound that can be heard inside of the car not really sure what i could call the sound but its loud enough that you could heard it few meters away its like a low sound instead of high pitched like outside of the car its sounds normal since fuel pumps do make noise when priming but no idea why it's so loud

[Shotter]

https://www.youtube.com/shorts/8pOgSgrc6IY there's a video of how the engine sounds when idling if there's anything you or someone would notice off about the sound.

[Mike Tries]

How old is the oil in there? Is it filled to capacity? What weight is it? It is hard to tell what I am hearing through phone speakers, but my thought was lifter tick. Low oil, or low oil pressure, or frothing oil could cause lifter tick--at least in some cars it does.

[Shotter]

How old is the oil in there? Is it filled to capacity? What weight is it? It is hard to tell what I am hearing through phone speakers, but my thought was lifter tick. Low oil, or low oil pressure, or frothing oil could cause lifter tick--at least in some cars it does.

oil has been changed recently and isn't leaking we put 4 liters which should have been enough. also wouldn't low oil pressure throw a code other than lean fuel mix ? ( we have used both 5w30 oil and 5w40)

[grayjay]

Re-reading your initial post, I would next check to see if you have a vacuum leak anywhere in the intake/PVC system causing the lean fuel condition and contributing to poor starting and cold running. Could also be caused by dirty fuel injectors. I find that a good running 1.8t starts well in cold. I have no trouble getting mine started when it has been out overnight at -10F/-23C.

[Cybersombosis]

Do me a favor and put a pair of vicegrips on the below pipe marked with an X going to the PCV check valve under the intake manifold and report back if that helps the idle issue.

IMG_1827.jpg

[Shotter]

Do me a favor and put a pair of vicegrips on the below pipe marked with an X going to the PCV check valve under the intake manifold and report back if that helps the idle issue.

IMG_1827.jpg

at first when i started the engine, when it was idling at 1300 rpm, from that it normally slowly goes to 900 rpm but when i put the vicegrips on the x you markted, the rpms dropped a lot instantly around 400 rpm and when i took them off they went back up again and slowly went down to 900 a bit later idk if it was a coincidence, ill try it again tomorrow morning, when the engine is cold, at 900 rpm it didn't seem to do anything tho.

[TobiqueSlang]

If you have misfires and the plugs have been changed I'd also look at replacing your ignition coils.

Also should take more than 4L of oil, off hand accounting for the oil filter it should take a little less than 5.5L of 5W40

[Shotter]

If you have misfires and the plugs have been changed I'd also look at replacing your ignition coils.

Also should take more than 4L of oil, off hand accounting for the oil filter it should take a little less than 5.5L of 5W40

Well the dipstick shows enough oil so that's good enough for me, gonna put the ignition coils to consideration, the car starts good tho, it doesn't take long to crank at all it starts up almost instantly after fuel is primed and it goes to 1300 rpm then it just shuts off, sometimes it tries to struggle to stay on after the engine is a bit more warm but sometimes there's just no sound and the engine is just off. i was thinking of taking it for a smoke test since i don't own a tester. do most mechanic shops tend to check ignition coils too, or can i do that at home easily? or should i just buy new ones and hope Xd

[codemode]

So you do have a cold start, your engine just doesn’t want to stay running. I don’t think it’s the coils. Is there a key symbol on the instrument cluster?

You mentioned having to press the accelerator to keep it from shutting off. It’s either running super rich or super lean.

Do you have a fuel pressure gauge? If not I would take the injector rail and see if there’s any leakage (ignition to acc). If not, I would try to crank the engine and put a cup under each injector to see how much fuel there is.

If that turns to be ok, I would disconnect the MAF and see if turns off. If it doesn’t, that would mean something is wrong with your mixture.

I don’t think a small vacuum leak would be enough to shut your engine off. It would have to be a massive one. How does your brake pedal feel? Does pressing it cause a SIGNIFICANT drop in RPMs?

Also having it scanned would be the best thing at this point.

[Shotter]

So you do have a cold start, your engine just doesn’t want to stay running. I don’t think it’s the coils. Is there a key symbol on the instrument cluster?

You mentioned having to press the accelerator to keep it from shutting off. It’s either running super rich or super lean.

Do you have a fuel pressure gauge? If not I would take the injector rail and see if there’s any leakage (ignition to acc). If not, I would try to crank the engine and put a cup under each injector to see how much fuel there is.

If that turns to be ok, I would disconnect the MAF and see if turns off. If it doesn’t, that would mean something is wrong with your mixture.

I don’t think a small vacuum leak would be enough to shut your engine off. It would have to be a massive one. How does your brake pedal feel? Does pressing it cause a SIGNIFICANT drop in RPMs?

Also having it scanned would be the best thing at this point.

There isn't a key symbol on the instrument cluster but there is a code for anti theft system immobilizer that there's sometimes no signal, we didn't go further into that since we didn't see how anti theft system immobilizer would cause a engine light to show up. Don't have fuel pressure gauge but a shop sells them near so i'll go buy one when i have the time, i'll check on the other things you said and give a update when i have the time

[Shotter]

Welp, fixed the cold start issue and the car no longer suddenly shuts off, works fine too, it was the fuel pump, we had taken it to a shop to change it around 6 years ago, they said they changed it and billed us but didn't change it..... It was still the original pump from 20 years ago when the car was made and was running poorly. anyways i still have lean code, but now no symptoms expect that the rpm meter is dancing when starting the car, it goes to like 1600 then back down to 1200 then back to 1600 and then settles at around 1300 after some time, before going back to 900. any ideas on that or do people even find their lean code problems.

[Mike Tries]

Grayjay mentioned dirty fuel injectors earlier. Consider testing and cleaning or replacing your injectors. If they're not flowing well, then the engine won't get enough fuel. Check all four of them. If they test well, check the harness that they plug into as well--those disintegrate over time. I'd think a weak signal due to degraded wires could cause inadequate fueling.

[Larhal]

easy way to tell if it is a fueling problem is to spay some carb cleaner in the intake. If it fires up it is fuel related.