brisyl

Hi all, my TT is acting strange, when i start it, the rpm is going up and down by around 500rpm three time and then it settle and been running good afterword and been like that for about a week,no check engine light, this morning when i left home it was running rough (like a miss) for about 10 min and then was fine. Did someone have an idea what would cause this?
Thanks

cheeba

You really need to scan modern vehicles before diagnosis – without it, it's almost always a crap-shoot. Logging timing, knock, fuel, boost, etc., when the issue is happening will also tell you exactly what's going on.

The fact that the engine is running rough for up to 10 minutes means it has nothing to do with the actual warm-up procedure of the car since it's entered into closed loop mode (running off of sensors) long before that. Are there any other symptoms? Anything going on with the temp gauge? If there is then you should replace the CTS (Coolant Temperature Sensor). Any work done to the car recently?

My guess would be the ignition system: coilpacks, wiring, plugs, etc. But it's just that – a guess. Without further information, anyone would just be taking stabs at the dark.

brisyl

Does the scan will read something if the check engine haven't come on? Yes my temp and fuel gauge have to be replace due to what it seem to be a common cluster problem, they dont give the right reading,but i will be at least one more month before i have the parts. As for the work done on the car,i don't know, i just bought the car 3 weeks ago.It only ran rough 1 time but the fluctuation in rpm is every time the car is stop for a few minute and then i start it up it will do it 3 time and then settle and will not do it until the car is stop again. i Tried it for about 10 times by starting and shutting down the engine and everytime it was doing the same patern 3 times. weird!

cheeba

Yes, there are many codes that will not trigger an actual CEL on the dash. Having access to the VAG-COM can also let you monitor things like voltage, knock, fuel trims, etc., which helps you diagnose combustion issues. A skilled mechanic will know what to check out for diagnostic purposes.

It almost sounds to be electrical in nature, due to the uniformity of the problem, but it wouldn't hurt to check out the vacuum system as well.

brisyl

Ok Thanks

jbrown

Hey Bud I got the same problem. The mechanics thinks it's the mass air flow that is indicating wrong numbers to the cpu, hence the fuel mixture is not adequate. You should then read a minus fuel trim (because the cpu is trying to correct the amount of fuel).

Unplug your MAF and keep it like that for a day or two, your TT's cpu will then set to a default mode, and it should get back to normal. If that's the case, you need to clean or change your MAF. If not, then I can't help you.

I am getting a new MAF tomorrow, so I'll let you know how are things working.

brisyl

Ok, let me know if it solve the problem

jbrown

Hey,

The mechanic replaced my old MAF with a MAF that was in a scraped car. I was not impressed, and the repairs obviously didn't do the cut.

I am keeping my MAF unplugged until I get a brand new Bosch MAF.


How did the unplugging worked for you?

brisyl

I haven,t unplugged it yet, the car is parked for winter.

jbrown

Alright, so I got a new MAF, but the problem is still there... So the MAF isn't the problem. It's got to be electronic since when I unplug the MAF, the car runs on "default" settings and runs good.

I got my car used, perhaps it is chipped. Maybe the chip is changing the air/fuel mixture, hence it's not the correct mixture to start the cold engine.

What do you think? What else has an electronic input on the mixture? Is there a gas sensor that could be misreading?