I have a 99 A4 1.8T...

It has recently started running pretty rough sometimes. So far I have not been able to distinguish any type of pattern. Sometimes it happens when the car is cold and has just been started for the first time, but it has also happened when the car is hot and near the end of the commute after being restarted a time or two.

It has happened in both wet and rainy conditions.

When this is happening - the idle RPM fluctuates - normally seems to idle right around 900 rpm, but it will dip well below and a few times the car has died and needed to be restarted, normally when it doesn't die, it revs itself up to around 1100 then drops again.

When it is doing this you have to really get on the accelerator when letting of the clutch or the car will stall, if you just drive normally, it will stall or nearly stall. You then need to often get on the gas pretty hard even when switching gears from 1 to 2 and 2 to 3 or it will feel like its going to stall, and there is a lot of hesitation.

When its having this issue, and you are driving at highway speeds in 4th or 5th gear, the car often hesitates - you can put the gas pedal on the floor and the car will not really respond for a few seconds.

It is not constant - i have made it all the way home from work (30 miles) without having any issues, and i have had issues the whole way. I have also noticed my fuel mileage is very very bad lately.

Also when the car is running fine the vac reads a little under 20inHg which should be normal but once the hesitation starts it reads 10inHg

Once hesitation starts and i floor it boost builds but car goes nowhere till the higher rpms like 4.5,5,6

All electronic connectors have been cleaned all coils and throttle body has been changed. The car has a giac chip stock intecooler and exhaust.

Even though the car didnt have an CEL i went and hooked up the tester it said Bank 1 Sensor 2 dont know the code number exactly.

PLEASE HELP !!!!

Thanks!

 

BTW I've searched the forums and the one thread that seemed similiar died years ago with no conclusion and I'm sure a lot of us audi drivers has had the same problem and wants to get it fixed

 

Bank 1 sensor 2 refers to your post-cat oxygen sensor. This sensor's only job is to make sure your cat is working properly by comparing it's readings to those of the pre-cat sensor. Can't imagine that would cause the hesitation and stalling issues you're experiencing, just sounds like it might be on its way out.

How's the maintenance on the car? Fuel filter? Spark plugs? Air filter? Sounds to me like its not getting good fuel, spark, air, or all three.

 

Also, how old is the MAF? Have you tried using MAF cleaner on it? Have you performed a boost leak test? (not likely the issue here, but can't hurt to try)

Do you have some sort of VAG-COM or just an OBDII reader?

 

yea the fuel filter was changed in aug along with the oil. The plugs and air filter not sure i will check. As for a boost leak test I haven't done one either my friend said its either a boost leak, cracked intercooler, or the giac chip, or tps ? The MAF has not been changed but i sprayed the connector. Is there a way to make sure i mean while the cars running i unplugged it then the car eventually died after a couple of seconds.

 

If your car dies without the MAF connected then the MAF likely isn't the problem... it should run at least decently without the MAF (but will throw a CEL). But it still wouldn't hurt to try removing the MAF sensor and spraying the sensor itself with MAF cleaner.

Have you performed a throttle body alignment? This will align the TPS, and it can be a cause for big issues. It would be ideal to perform this with VAG-COM so you can make sure it doesn't fail, but without VAG-COM all you have to do is turn the key to the ON position and leave it in that position for several minutes (without starting the engine during that time).

 

ok i'll try that,my cousin has lent me his cable and i believe its a 16 pin, but I'm wondering where theres a software download I can get to use that cable. I mean I've seen rosstech website but I have no clue in which one to download.

 

There should be a free VCDS download on Ross-tech's website. IIRC this will allow you to read codes, but not clear them or read measuring blocks.

 

Ok so after a whole bunch of trial and error with the vas 5052 program. We came to the conclusion that it was my MAF. It seems when the air filter was changed, an oil based product was used to clean it. Because of that oil base residue, the inside strip in the MAF got messed up and caused it to act ridiculous randomly. We changed out the MAF and she's running like a champ. BTW if anyone has the issue of the temp gauge going back and forth between the middle and 1st notch of the C and H its not necessarily a bad temp sensor it just maybe the thermostat is stuck open which is common. So becareful if you get your car serviced for an air filter make sure (no oil based products are use to clean it). As for the tps calibration after 20 startups or so it does it on its own.

SO THANK YOU FOR YOUR HELP Chao !

btw if anyone is in the Atlanta area check out MMT EuroTech!

 

Cleaning the IAT sensor & throttle body fixed a similar issue with my B5 1.8t.

I had replaced an n75 valve, hoses, MAF, spark plugs, & used fuel injector but it didn't help. I had timing belt, valve cover gasket and other fixes done for routine maintenance and that didn't fix it either.

It looks like oil probably leaked from the valve cover gasket and got into the IAT sensor. The build up in the throttle body was pretty bad too.