04 A4 1.8t cold start issue...

[lonz]

Hey guys, I've got a problem that's left me scratching my head My Audi has been having an issue with cold starts the last month or two. I turn the key to the on position, let the fuel pump prime. Try to start it and she's just crank no start. I'll turn the key off then back to on and try again and she fires right up. No problem. Its like this every cold start in the morning or cold evenings. When it's warm out or the cars warm there's no issue. I've already replaced the things I suspected to be the issue. Cars got a new high flow fuel pump. New fuel filter. New 2.0t coil packs. New spark plugs. New cam position sensor. And I replaced the fuel pump relay switch inside the dash. The MAF is the only thing I haven't replaced yet but I did remove it and do the DIY alcohol cleaning trick. The only way I can get it to avoid the cold start issue in the morning is to unplug the MAF, start it (she fires right up) then plug the MAF back in before it throws a code. Does anyone have any other ideas? I'm at a loss and hate to just keep throwing money at this.t hanks for any help.

[jacobsen]

I think you discovered your issue by unplugging the maf.

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[lonz]

That's what I was thinking but wanted to ask the group before I spent another $180 on a new MAF

[jacobsen]

I understand. That's a good idea. Sounds like you got the change in Behavior you were looking for. But maybe still wait for OG , diagnosticator or someone else to chime in. But it does sound like you figured it out already.

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[lonz]

Well I just bought a new MAF, $112 from ECS tuning. Should be here in a few days. Hopefully that was the issue. Thanks for your input Jacobsen

[jacobsen]

I hope the maf does the trick.

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[MetalMan]

Another possible culprit is the coolant temp sensor located in the coolant flange at the back of the head. If you have VCDS or any generic OBDII reader you can watch that sensor's behavior and see if it could be at fault.

[mmasire88]

Another possible culprit is the coolant temp sensor located in the coolant flange at the back of the head. If you have VCDS or any generic OBDII reader you can watch that sensor's behavior and see if it could be at fault.

+1 To this!

In my experience the coolant temperature sensor can do all kinds of funky things to your car. I was chasing a misfire for 4 months on one of my A4's, I was driving it one day and I saw my temperature guage peg 0 then back to normal, ran home, grabbed a spare green temp sensor and it was right as rain.

On the other hand, I'm leaning more towards a MAF in your case. Mostly because you say the car starts fine without your MAF plugged in. That tells us it's, most likely, not getting a proper reading from the MAF when it's plugged in. When you unplug the MAF it's using probably using some sort of secondary air/fuel mapping(limp mode).

[NYDCB]

I have the same issue. 2005 A4 1.8TQM. It does it 60% of the time on cold starts.

* Crank...no ignition unless I crank it for over 3 seconds. Tapping the gas seems to help.
* If it starts the first time, the EPC light comes on.
* At this point I turn the car off.
* 2nd crank starts right up with no issue, no warning lights.

[old guy]

Another possible culprit is the coolant temp sensor located in the coolant flange at the back of the head. If you have VCDS or any generic OBDII reader you can watch that sensor's behavior and see if it could be at fault.

This is very much a possibility ↑. Unfortunately without some way to monitor its activity the only way to know for sure is to replace it.

[lonz]

I plugged in my OBDII reader on the way home from work and again this morning and didn't notice any abnormal temp readings. I'll keep an eye on it in the mean time though. I hope that sensors ok, I replaced the rear coolant flange last year when it started to leak. What a pain in the ass lol. My MAF should be here in a few days. Thanks for all the input everyone, that's why I came here.

[MetalMan]

I plugged in my OBDII reader on the way home from work and again this morning and didn't notice any abnormal temp readings. I'll keep an eye on it in the mean time though. I hope that sensors ok, I replaced the rear coolant flange last year when it started to leak. What a pain in the ass lol.

Have you looked at the coolant temp readout while the engine was cold and giving you the cold starting issues

[lonz]

Yes only the one time though this morning. Yesterday after work the car started on the first try no problem and the readings seemed normal.

[ehhfour]

I'm currently having the same issue as the OP. In the mornings when it's cold, I'll try to crank the car and it has a hard time starting. When it starts, it'll immediately die. Sometimes it'll stay running for a bit, then I'll blip the throttle and it'll die. Much to the displeasure of my starter, after trying to crank the car over multiple times (between 3-6), the car will finally stay running, and run pretty smooth.

Similar to the OP, I started by changing my fuel pump, fuel filter, spark plugs and coils. The issue still remains.

I plugged in my VCDS cable and ran a quick diagnostic and it came back with the following;

17700 - Map Controlled Engine Cooling Thermostat (F265)
P1292 - 004 - Open Circuit - Intermittent
16500 - Engine Coolant Temp. Sensor (G62)
P0116 - 004 - Implausible Signal - Intermittent
18010 - Power Supply Terminal 30
P1602 - 002 - Voltage too Low - Intermittent
Readiness: 0000 0000

After doing some research, I'll be changing my coolant temp sensor and thermostat to see if that corrects my hard starts.
I wish I would have scanned first before changing the pump, but the car didn't have a CEL on so I never even thought to use the cable.

[jacobsen]

I replaced both my bad coolant sensors and my tstat but never had a starting issue. Wonder if it's because of the apr tune?

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[lonz]

Well I've had the Apr stage 1+ since I've owned the car 7 years ago so it shouldn't be that. The new maf will be here on Tuesday thankfully. Hopefully that's the solution

[RDA990]

I'm currently having the same issue as the OP. In the mornings when it's cold, I'll try to crank the car and it has a hard time starting. When it starts, it'll immediately die.

The same thing has happened to mine since I bought it from the previous owner, but only if I put the car on "Drive" or "Reverse" while the car does its 1 or 2min warm up cycle. After that cycle it's fine. It's a completely separate issue than the one in here so I'll have to make a thread about it soon...

[ehhfour]

I changed out my coolant temp sensor with a new one from Audi. Car started up first crank this morning despite being a pretty chilly morning.

So far so good, but I'll be changing the thermostat this weekend just to complete some maintenance.

[MetalMan]

hope that wasn't a fluke and it keeps working!

[Gberg888]

Same issue.

Looks like a maf, thermostat and coolant temp sensor need to be changed on my car. Ill do the temp sensor and thermostat first though.

[lonz]

Well damn; got the new maf installed and the car runs better but the original cold start issue persists. I guess next is onto the coolant temp sensor...

[lonz]

Wonder if I should just install a new thermostat while I'm at it and have the system drained. When replacing that temp sensor on the rear coolant flange do you need to do a full drain on the coolant system or only a partial?

[jacobsen]

Wonder if I should just install a new thermostat while I'm at it and have the system drained. When replacing that temp sensor on the rear coolant flange do you need to do a full drain on the coolant system or only a partial?

It takes about 5 minutes to replace the top side green sensor. There might be an updated part number for it. No coolant needs to be drained. The bottom side will drain if you remove that one. Just be quick with swapping them out and lube the new oring with silicone grease before you push it in. It's held in by a plastic clip, some come with a metal clip now.

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[NYDCB]

Man, I hate when I have someone in the car. I say a prayer as I crank lol! "Don't worry... This is normal..." has come out of my mouth quite a few times. Starting up on the 2nd try is fairly common at this point.

[jacobsen]

Man, I hate when I have someone in the car. I say a prayer as I crank lol! "Don't worry... This is normal..." has come out of my mouth quite a few times. Starting up on the 2nd try is fairly common at this point.

Just like Biff from Back to the Future

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[lonz]

Looking through my notes, I see I already replaced the upper temp sensor when I replaced my rear coolant flange last February. But I believe the lower temp sensor is still the same One.

[Dappa01]

Looking through my notes, I see I already replaced the upper temp sensor when I replaced my rear coolant flange last February. But I believe the lower temp sensor is still the same One.

It sounds like ur fuel pump the check valve is bad (I see that seem symptoms on BMW's all the time) and u may have a clogged fuel filler. If u have access to a fuel pressure gauge check ur fuel pressure.

[lonz]

It sounds like ur fuel pump the check valve is bad (I see that seem symptoms on BMW's all the time) and u may have a clogged fuel filler. If u have access to a fuel pressure gauge check ur fuel pressure.

I just installed a new Bosch 040 "High-Output" Fuel Pump and new fuel filter just a few months back so I'm hoping it's not that. But fueling is definitely an option.

[NYDCB]

Fuel filter is on my very short list of things to do. Still has the original is my guess...

[ECS Tuning-Audi]

Last winter I had A cold start issue. Was the coolant temp sensor. Be sure to replace with a genuine Audi sensor as some of the aftermarket ones don't last too long.

Jason

[lonz]

Last winter I had A cold start issue. Was the coolant temp sensor. Be sure to replace with a genuine Audi sensor as some of the aftermarket ones don't last too long.

Jason

Well I just bought the coolant refresh kit you guys sell and a second temp sensor. Figure if I'm working with the system I might as well replace both sensors and the thermostat while I'm at it.

[jacobsen]

Could the high flow pump and fuel filter regulator be at odds? Any vac leaks? How did you Plumb your fuel pump? Could this have something to do with the fuel tank? Does it happen no matter how much fuel is in the tank?

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[Dappa01]

I have a question when the problem occurs if u keep cranking the engine does it start?

[lonz]

I have a question when the problem occurs if u keep cranking the engine does it start?

On a cold start when the issue occurs I can crank and crank on the first start as long as I'm comfortable with(don't want to burn up the starter) and it doesn't start up. Sometimes it will try to. Very rough idle for 2 seconds then dies. In both instances it always starts right away on the second time I try to start it.

[lonz]

Could the high flow pump and fuel filter regulator be at odds? Any vac leaks? How did you Plumb your fuel pump? Could this have something to do with the fuel tank? Does it happen no matter how much fuel is in the tank?

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Fuel level never seems to matter. Just outside ambient temp. Like this morning was 60deg out and she fires right up. Yesterday morning was 52deg and it would start until the second try. The fuel pump is a drop in unit that hooks up to the existing plumbing. Id be surprised if it had to do with the pump because it started just fine for 4 months before this issue arose. I don't believe I have any vac leaks.

[old guy]

Before your next cold start try this. Turn the key to on and wait a few seconds. Then turn the key to off. Repeat this three or four times. The fuel pump only primes for a second or two and then stops. It doesn’t start again until you are cranking the engine over.

If this corrects the failure to start on the first try the problem is with the fuel system resting pressure. You could also confirm this with an inline fuel pressure gauge. ECS has one that is relatively inexpensive.

[ECS Tuning-Audi]

Well I just bought the coolant refresh kit you guys sell and a second temp sensor. Figure if I'm working with the system I might as well replace both sensors and the thermostat while I'm at it.

Can't go wrong with preventative maintenance!

Jason

[lonz]

Before your next cold start try this. Turn the key to on and wait a few seconds. Then turn the key to off. Repeat this three or four times. The fuel pump only primes for a second or two and then stops. It doesn’t start again until you are cranking the engine over.

If this corrects the failure to start on the first try the problem is with the fuel system resting pressure. You could also confirm this with an inline fuel pressure gauge. ECS has one that is relatively inexpensive.

I'll definitely try that on the next few start ups. If that is the case, how do I go about fixing it?

[lonz]

Well old guy I've spent the last few mornings trying what youve suggested and it seems to have temporarily fixed the issue. So now the question is how do I fix it from here? Been doing alot of reading about it and have gotten a wide range of solutions. Any thoughts?

[jacobsen]

Well old guy I've spent the last few mornings trying what youve suggested and it seems to have temporarily fixed the issue. So now the question is how do I fix it from here? Been doing alot of reading about it and have gotten a wide range of solutions. Any thoughts?

It sounds like your fuel pump check valve may not be maintaining the pressure between the time it takes to Prime the fuel system upon key on and when you begin to crank the vehicle to start. If you did this and one Fell Swoop meaning you turn to the key from totally off with the key out to be in and to cranking position your fuel pump may not have enough pressure to fill the cylinder is fast enough. Can you describe the way in which you performed the procedure? Did you put the key in and allow the fuel system to Prime with the key in the on position? Did one time work or did you do it multiple times?

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