warm start issue 1.8t

[seany26]

back again with yet another warm start issue.
this past few months the car has been having a problem after its been heat soaking on a warm engine, only on hot days like 2day! i'd drive te car about the town doing whatever then park up for say 30-40 mins and when i come back to start it , it idles really low and may cut out. throttle is non responsive unless i hold it down for 10sec and it slowly builds the revs an then everything is back to normal. if i switch off and hold the throttle while starting to give it an immediate high rev kick its fine also. once i do that i will start just fine after that.
automaticaly im thinking it was something to do with the breather system so i checked all the vac lines and pcv non-return valve but all was clear!

anyone any ideas please share, im all ears.

 

[sabaxter]

Check your fuel pump fuse sounds similar to an issue I had! Otherwise check your maf sensor. Thats where I would start.

 

[Broken Byzan]

CTS

 

[ShaunS3]

CTS (Coolant Temp Sensor)

Very common issue on the 1.8T

Shaun.

 

[seany26]

CTS (Coolant Temp Sensor)

Very common issue on the 1.8T

Shaun.

ok will check it 2moro but dont see how it would stop throttle response at high temps. would understand if it was not cold sarting correct or erratic idling all the time.
thanks

 

[pauldazzle]

VCDS diagnostic would be a good idea.
CTS is always a prime suspect for temp related starting problems. If you have the old black type CTS I'd change it out regardless as it will fail at some point. N.B. Fit a genuine VAG revised green CTS only.

 

[seany26]

OK today especially this is really f**king me off, start the car after its been sitting heat soaking and revs dip with no throttle response at all! no fault codes at all, CTS is reading what it should be. even when i watch the throttle pot on VCDS it don't move at all. tried unplugging the MAF also and no difference and as i said before if i hold the throttle flat to the mat when i start the car and give it a good rev it clears it, WTF!

Anyone had experience of this before.

 

[seany26]

Check your fuel pump fuse sounds similar to an issue I had! Otherwise check your maf sensor. Thats where I would start.

Did you mean the fuel pump relay, because that may be my issue. im sure it controls lots of other things.

on second thoughts it would not start if it was this, mine is starting fine!

 

[pauldazzle]

Throttle body or accelerator pedal fault would be my guess. The fact that when you monitor the throttle pot you don't get a change would say to me that you've started to pin the issue down.
You can't totally rely on fault codes for diagnosis as there are several sensors that wil only cause the ECU to throw a code for when if they become intermittent or short to ground. MAF & CTS sensors are prime examples of this as if the ECU is still getting a signal from the sensor it doesn't recognise a fault. I'm not sure, but this could also be the case with the TB & pedal.

 

[seany26]

I know you would definitely think that, before I start the car everything moves fine, throttle position says 2% then goes to zero when I start the car. Think when it idles normally it reads something like 14%. It's like it's closing when I start the car and getting stuck. Maybe the heat is starting to effect the spring inside the TB or something.

 

[Larry_Fopps]

Did you ever figure out this issue, I'm currently experiencing the identical issue. Cold Start car drives fine, Warm start, starts fine but no throttle unless I hold my foot on the throttle and it slowly builds up, or if i shut the car and start it with my foot giving throttle.

 

[audi-a6]

Unplug the cts.... Then try, I had the same problem, remember there is more than one sensor...

 

[Larry_Fopps]

Unplug the cts.... Then try, I had the same problem, remember there is more than one sensor...

Appreciate that. There's only two correct? The 4 pin in the coolant flange, and the 2 pin in the lower rad hose? Any others i'm not thinking of? The one in the coolant flange on the back of the motor I just replaced when I replaced the flange 2 weeks ago. That didn't solve the issue.

 

[audi-a6]

Appreciate that. There's only two correct? The 4 pin in the coolant flange, and the 2 pin in the lower rad hose? Any others i'm not thinking of? The one in the coolant flange on the back of the motor I just replaced when I replaced the flange 2 weeks ago. That didn't solve the issue.

Was it replaced with a genuine audi one?

 

[Larry_Fopps]

Was it replaced with a genuine audi one?

Yes it was, from the dealer, so it was the most recent revision. Are there any other coolant temp sensors i'm not thinking of. OP was the Coolant Temp Sensor your issue?

 

[audi-a6]

Yeah it was, on my a6.... I had 4 sensors, but it was the 2.7t engine

 

[Larry_Fopps]

I'm hoping Seany26 logs in and sees this. I'm very curious to see what his solution was on the b6 1.8t.

 

[seany26]

I'm hoping Seany26 logs in and sees this. I'm very curious to see what his solution was on the b6 1.8t.

no did not get back to this yet as it has not happened again due to the weather not being warm enough here yet!
my next port of call was to back pin the plug on the throttle body and check that voltage was getting to the motor on the TB, this will tell me for sure the TB is faulty or not. i suspect the motor is going faulty under very warm heat soak!
have you logged it on vcds yet pedal vs throttle poistion?

 

[Ovid]

should be around 15% with engine off and ignition on.

Firstly give the TB a good clean open up the flap and get all carbon residue off, once you have done that follow this guide.

http://wiki.ross-tech.com/wiki/index.php/Throttle_Body_Alignment_(TBA)

 

[Larry_Fopps]

I'll be doing a TBA tonight. I just cleaned it a week ago. I truly do not think a throttle body alignment will solve the issue as its perfect on cold starts and only warm starts that its an issue, but I'm going to do it regardless. Also, I'm going to log gas pedal vs throttle body position in VCDS as well and see where that gets me.

 

[seany26]

I'll be doing a TBA tonight. I just cleaned it a week ago. I truly do not think a throttle body alignment will solve the issue as its perfect on cold starts and only warm starts that its an issue, but I'm going to do it regardless. Also, I'm going to log gas pedal vs throttle body position in VCDS as well and see where that gets me.

Just thinking you could have a weeping injector, take the fuel rail out with everything connected after say a 20min heat soak and a hard run before hand and look for any signs of slightly leaking injector. done not overlook this one!

 

[Larry_Fopps]

Just thinking you could have a weeping injector, take the fuel rail out with everything connected after say a 20min heat soak and a hard run before hand and look for any signs of slightly leaking injector. done not overlook this one!

I have no issue with starting. If it were a leaking injector, it would be hard to start and i'd have misfires upon start up. I just have a low idle and no throttle on warm start ups. Also the injectors are brand new injectors. 2000 miles on them at this point. Truly do not believe that is the issue.

 

[pauldazzle]

Cam position sensor failure is a common source of hot start problems.

 

[Larry_Fopps]

The thread title is deceiving. Its not an issue with Starting. Its an issue with Throttle once when warm starting.

 

[pauldazzle]

Have you removed & cleaned the throttle body yet?

 

[Larry_Fopps]

Have you removed & cleaned the throttle body yet?

Yes, Throttle body was removed and cleaned. Then later on, after that didn't help, I swapped it out with a different, known good throttle body.No dice.

 

[Larry_Fopps]

So i gave up and brought the car to the shop that did the tune since they are a unitronic dealer as well as a performance vw / audi mod shop. After 2 months, they decided that it was the ecu. I got a new ecu, different part number from a 5 speed 03 instead of my 04 6 speed. Defeat the immobilizer, and we were waiting on unitronic to transfer the tune to the new ecu. In the meantime i was driving around on the stock tune, and didn't have the issue. Today i went back, they put the tune back on the car, and the issue came right back. This time worse than it ever was as the temperature was nearly 90 degrees Farenheit today. Also, now my boost was really wonky, boosting higher than ever before like 23psi at times, and then dropping off and just all over the place. I'm at a loss.

 

[pauldazzle]

Sounds like it's a bad map then.
Never ever heard of Unitronic in 8 years of activity on VAG forums.

 

[Larry_Fopps]

They are based out of Canada and very popular here in the states. Are you saying bad map of the tune or map sensor. I think it's the tune.

 

[Larry_Fopps]

I did some logs today and upon throttle loss i put my foot to the floor. Pedal position read 100% throttle position read 14%. I don't suspect the throttle body because i've already swapped it. In my logging today, i noticed my maf was only reading 1.7 g/s and I've been told it shouldn't get below 3g/s. I'm going to swap that tomorrow with one i have on another car and see if that changes anything.

OP has your issue come back.

 

[Larry_Fopps]

Well, four months to the day that this started happening for me, I think i've finally cracked the case. Granted it was at a shop for two full months where nothing was solved. While waiting in line for gas yesterday with the car idling, once it was time to move up, throttle was just about completely gone. I pulled up to the pump shut it off, and filled up. Started it back up to leave and no throttle. I Limped into a spot and popped the hood. Now that i've pretty much determined its something heat soak related and I already swapped the throttle body, maf, and ecu, I decided to try pulling the connector on the IAT. As soon as I did that idle rpms came up to normal and throttle returned. plugged it back in and throttle was gone, unplugged again, throttle was back. I'm going to swap the sensor tonight just to confirm but looking very likely that's the issue.

So OP, if you are still having this issue, when it comes up, unplug the IAT.

 

[Larry_Fopps]

IAT did not solve the issue. The journey continues. I definitely think i have a vac leak, so targeting that is next on the to do list, even though thats not causing this issue. I'm seriously starting to think the tune is the issue, but going to get to the cause of the rear o2 codes before i go back to stock.

 

[seany26]

IAT did not solve the issue. The journey continues. I definitely think i have a vac leak, so targeting that is next on the to do list, even though thats not causing this issue. I'm seriously starting to think the tune is the issue, but going to get to the cause of the rear o2 codes before i go back to stock.

Reading over this thread( sorry I've been stuck sending pm's) I really think it is your tune. Don't bother getting to the bottom of the rear o2 codes as that is most certainly the tune, they have not been deleted correct when you swapped your ecu over.
that is maybe why my problem has went away because I've changed my file.
have you any idea what the version of ECU that you have?
vcds will tell you under engine, or in a auto scan.

 

[Larry_Fopps]

I actually put the stock ECU, injectors and plugs in the car last night. So far, I'm on two warm starts with no issue, however I do not have my hopes up yet at this point. In doing so, I found a vac leak which probably explains why my maf readings are so low. I have the 034 kit on the way, because i know that if this hose went bad, the rest of the system probably isn't far behind.




I currently have the rear o2 unplugged still. I just want to ensure that it is running correctly, no throttle issues, and confirm that issue is good, and then i'm going to get to the bottom of the rear o2.

If that rectifies the situation, I'll throw the injectors and the other ecu back in and see what happens I figure that's a good way of pinpointing the tune.

Is it possible that a vac leak could cause the issue due to such low maf readings on the tune but not throw a code, and then unplugging the IAT returned throttle? Doesn't really make sense to me. But we shall see how this pans out.

 

[Ovid]

yes that can cause it

 

[seany26]

Yes vac leaks can play havoc on idle issues and trims.
Are you sure that is a vac line, looks like the breather T from the the rocker cover to crankcase? I may be wrong, get it fixed anyway and see how it pans out.

 

[seany26]

I currently have the rear o2 unplugged still. I just want to ensure that it is running correctly, no throttle issues, and confirm that issue is good, and then i'm going to get to the bottom of the rear o2.

I would plug the rear o2 in now that you are running stock, will tell you if the tune has something to do with it throwing the code.

 

[Larry_Fopps]

I actually meant to do that tonight when i had the hood open and forgot. I'll plug it back in tomorrow and clear the codes and see what happens. I logged the maf tonight, same readings as the tune, 1.7-1.9 at idle, has to be because of that hose thats split open. 034 kit should arrive tomorrow we shall see if replacing that hose raises maf readings.

 

[seany26]

Have a look at your fuel trims before clearing the codes, that will tell you if that breather hose is effecting anything. It should be out of wack because you will be pulling in unmetered air via that breather pipe leading to the TIP.

 

[Larry_Fopps]

My issue was in fact my tune. Stay away from unitronic stage 2. I've come across another person having this issue with that file. Switched to Apr and haven't had the problem since.