A3 TDi cold start misfire

[lewis88]

Hi, lately I've had a problem with my A3 TDi running really rough when started in the morning. it sometimes idles lower aswell as lumpy and when driven it will get to 2000rpm then feel like it has a really really bad misfire (and sounds like its hitting a rev limiter) then if you floor it it shakes the car really badly then will run on full throttle. changed the MAP sensor, temp sensor, have tried unplugging the MAF and have run VCDS and it has no fault codes other than an ABS sensor that i already knew about. turbo has recently been cleaned. runs fine after it warms up slightly but runs awfully when started from cold. any one had any similar issues? or know where to start looking next?

 

[Lewis583]

Check the glow plugs.

Easy way to test is a follows. (you will need a test light similar to below)

Remove all feeds to glow plugs.
Connect clamp end of test light to positive side of battery.
Touch probe end of test light to one glow plug terminal at a time
If glow plug is okay the light will illuminate, if they're knackered it won't light up. Perform test on all glow plugs

 

[colicabcadam]

i thought glow plugs just warmed the cylinder up prior to starting, to do nothing other than help it start

they do not stay on once the engine is running, so why would it be them ?

 

[Lewis583]

Not 100% sure on VAG diesels, but on some other marques the glow plugs stay on for a duration after the engine has started, to help maintain cylinder heat and idling.

It's a simple enough test to do, so will rule them in/out quickly.