ERRATIC/ROUGH IDLE ON COLD ENGINE START....HELP!?

[STYLEZAU]

Hi guys. I have been experiencing some annoying rough/erratic idles on cold engine starts. RPMs are jumping between 400 and 1000 until the needle settles at 800 after 30-40sec (see video). Engine/exhaust sound like a tractor during these first seconds and engine seems to stall almost. This only happens when the engine is absolutely cold (early mornings mostly when I haven't been driving for at least 6-8 hours). There are no problems when the car is warm and I cannot tell any difference while driving (maybe less low end power but I might be imagining things).



This whole problem started 2 months after I bought the car (was bought Feb 2012 new). I bought it to the dealership the first time and they replaced the camshaft control solenoid and timing cover gasket under warranty. Problem persisted so I brought it back...they repeated the process as they said they probably ripped the gasket while installing...yay...

Problem persisted and I brought it back a third time demanding this problem to be fixed once and for all. They kept the car 3 weeks and had several (according to them) conference calls with Audi Germany and other "experts" to find the root of the problem. In the end they replaced the injectors, the fuel pump and "cleaned the whole engine bay" (their words). FINALLY....the car started normally. This was October/November 2012.

Now for the last two weeks the problem slowly came back, getting worse every day.



I am thinking dirty throttle body/Idle air controller that keeps coming back ??? Or maybe a vacuum leak that wasn't discovered. Or defect coolant sensor. I don't want to go back to Audi again atm. They kinda p*** me off at that dealership.

Already tried coil packs and spark plugs...no change with new ones. Cannot locate any boost leaks through VAG-COM. No fault codes present.

If I cannot locate the problem myself I might take it to my local APR tuner to have a go at it.


Maybe somebody is familiar with this problem? Oh yeah...the problem already occurred when the car was fully stock.

Cheers!

 

[STYLEZAU]

So the MAF seems to be the culprit here. I disconnected it before starting the car this morning and it started just fine, no idle issues, no stalling. Switched off the engine, reconnected the MAF and tired again....stalling, erratic idle.

Gonna have to try a mate's MAF to confirm and then see if it can be fixed with a simple clean or need replacement.

Never thought it could be the MAF as the car drives fine except for the cold start problems. Who knows maybe I will feel an improved throttle response or something after changing it?!

No fault codes in VCDS.

 

[MrLapou]

Well done finding the possible cause of the problem.
A faulty MAF normally does not come up with a fault.
Disconnecting it, then running the engine will flash up a fault in the ECU and or may cause the ABS light to come on.

 

[Marshy]

Maybe it's the air temp side that's faulty which I'm suers part of the maf

 

[JaCkPoT]

please keep us informed as my car does this sometimes but rarely, also upon cold start... i just keep my foot on the gas at about 3k rev for 10 seconds and it seems to settle

 

[STYLEZAU]

Gave the MAF a clean but didn't improve. Then checked with a working MAF of a mate's car...still no luck. Same problem. So even though the engine runs perfect with the MAF unplugged, the MAF is not the issue. Also did a reading on the throttle body and realigned it using VCDS...all parameters seem to be fine and in line with factory/vehicle specs (also doubt its carbon build up in there as revving the engine on start up doesn't really help unless I do it for 10 or more seconds to warm the engine up).
I will check the coolant sensor next (see if data matches ambient temperature on cold engine). If that turns out to be fine I will do a pressure test and smoke test to see if there are any vacuum/boost leaks (more concerned about vacuum leaks in that case, doesn't feel like boost leak).
After that I could only think of air intake sensor or a dirty/defective Idle Air Control.

I don't believe its the fuel pump or fuel injectors again....very unlikely for these parts to fail again after only 5000km or less. Also cam seem unlikely as parts have been replaced there in the last 5000km.

Lambda sensors? Unlikely I guess.

 

[S3Alex]

Mine had similar problems a few months back.

The redundancy built into these engines is amazing as the list of wonky probes built up.

AMD found the thermostat was stuck open,MAF dirty but working,lambda probe giving dodgy readings and the real culprit was a throttle body fault causing the car to massively over fuel and idle badly or stall.

 

[Marshy]

Lambda sensors shouldn't come in to play until the car gas warmed up .
Have you logged your low fuel pressure when starting from cold?
Worth checking if you have vcds

 

[STYLEZAU]

So checked a lot of things today with VCDS and visually.

Double checked that spark plugs are alright, checked for vacuum leak/boost leaks (none), checked coolant sensor and lambda sensors (booth give correct readings), checked TB for residue but seems alright. Checked MAF again with VCDS...all good. No fault codes, no abnormal readings, no misfires in the log.

I am lost now. Cant think of anything else. Will talk to my APR dealer next so he can have a go at it.

 

[STYLEZAU]

The sound in the video is the APR turboback system which sounds like misfire/wrong air/fuel mixture. It kind of sounds like gasping for air/fuel. Hard to describe. The sound itself is nothing to worry about though.

I check my fuel pressure with VCDS while cold/starting up/warm....all normal.
Checked battery voltage and alternator...all good.
Now my last thing which I did, half by coincidence, half to rule a fuelling problem out, is change my fuel from VORTEX 98 (local Caltex Australia brand) to United 100RON. After refuelling I did an Adaptation 00 Reset with VCDS to reset all learned value (including fuel trim) to factory settings.

To my surprise the car started absolutely normal this morning and seem to have much better throttle response and less hesitation between gear shifts. I really really hope that this was the problem all along. Will see tomorrow. I found a few threads in different forums about Vortex fuel quality...apparently quite a few people had issues with it.


EDIT: Fuel and reset solved my problem...finally! Must have been contaminated fuel and not just the one batch as I always fuelled my car at the particular service station....gonna avoid them now and stick to 100RON.

 

[s3_revo]

So glad you fixed this issue, I am currently having this problem now with mine and am so baffled as everything seems to be all in order. I always use the same fuel never Shell V-Power

 

[xaudi]

wow, cant believe if the low RON fuel caused this. will check what comes up

 

[xaudi]

As I checked around and only find 95Ron max, shell vpower, caltex, BP. don't know what do with this now....