cJared3b

Hello everyone. Im Jared. I recently acquired an 03 A4 1.8T Quattro. When I got married, my wife added this car to my stable. Its a fun car, but has a number of issues. Ive been lurking for a while and can only find the same problems I have, but no solid answers. I finally decided to join with hope that yall can help me make my wifes car reliable again.

First off the CEL is on. I scanned it a while back and remember the 420 code and a couple others for low coolant temp, O2 sensors and Cat.

The car sometimes doesn't want to start. It cranks, but wont fire up. I usually cycle the fuel pump hoping to increase fuel presure if thats the issue and then start cranking. It slowly increases rpm until it fires up. Sometimes it idles smooth like nothing happened, but more often than not it idles rough for a while. As if it has a miss. Sometimes it fires up on the first try, but idles rough, and sometimes it starts up and runs perfect. Its very intermitant. Majority of the time it runs fine. Just the other day my wife and niecewere leaving a park and when she tried to leave the car wouldnt fire up. She sat ther for 10 minutes cranking and waiting, cranking and waiting until it finally started, then she said it was idling so rough and had such little power that she could barely move. She feathered the clutch until it was up to speed then eventually it cleared up and ran fine.

Another issue is when accelerating, I must be easy on it, or it will stumble. It accelerates fine as long as I dont push it too hard. When it does stumble the CEL flashes. I counted and it always flashes 16 or 17 times. This happens at highway speeds or slow speeds. I havent been able to floor it and see how this car is really supposed to accelerate.

Im hoping someone on here has experienced these same symptoms and solved them and can tell me what exactly fixed the problems.

Recent repairs: water pump, thermostat, timing belt, coil packs(4), spark plugs, fuel filter air filter and other obvious PM parts....oil...filter...etc.

I suspect a failing fuel pump?? Clogged cat?? Obviously I got the code for the cat, but these codes come from the O2 sensor which also has a code. I cant afford to replace the wrong part.

I grew up working on cars and have been a mechanic ever since. Ive worked on plenty of BMWs, but Im new to Audi. I appreciate your help.

Thanks, Jared

cJared3b

Sometimes when it finally fires up after having a hard time starting it idles high. Around 2-3k rpm for several minutes.

cJared3b

Anyone, anyone?

cJared3b

Bump

lyleswk

I would start with the looking for leaks in your exhaust or intake. Could be causing the problems you are having. Below is a link to the code you said you had.

http://wiki.ross-tech.com/wiki/index...4/P0420/001056

cJared3b

Thank you for the suggestion. Im a noob to forced induction, so bare with me....in what way would an air intake leak cause the hard starts? Are you saying its MAF and/or TPS related issues due to a leak or issues with boost? I dont hear exhaust leaks, but Ill get under it and listen closer.

Thanks again for your effort lyleswk


Are there o2 sensors after the cats? What are thoughts on hollowing the cats as an alternative to replacing them?

lyleswk

Forced induction really doesn't change the issue except the intake pressure part of the equation changes. Anyway, with a leak in the intake, you are leaking out some of the expected air volume (which is provided by the MAF) / pressure that the ECU is expecting, so as the unmixed air passes the injectors and mixes with the fuel, the fuel / air mixture the ECU is expecting is not met as it goes into the piston cylinders. In the case of a leak in the intake, generally the mixture would be too rich. As a note, vacuum or intake leaks are very tricky and there is no solid way to dignose except to inspect and fix anything that looks astray. Could it be the MAF? Maybe, but you generally get a code for that specifically.

As far as your O2, the O2 faults are defintiely easily expalnable given the explaination above. The This would then "confuse" the O2 sensors which would trigger faults on them.

As far as O2 sensors, I believe there is one before and after the cat. The ECU compares the two values to determine if the cat is working at the expected efficiency. This is what is causing your cat fault.

Hollow out the Cat (also known as installing a "test pipe")? There are several writeups on how you have to trick the ECU into thinking there is a cat in there and has to do with putting spacers on the O2 sensors. I have not done this out of fear of not being able to get the car registered becuase if the guy that does the inspection visually inspects and sees a downpipe versus a cat, big fines could be headed your way.

My 2 cents on the subject.

gimik

all due respect to lyleswk, i dont think a vacuum leak alone would cause your starting problems.. (also, usually i'd expect more codes). if you haven't already you should probably replace your coil packs (there was a recall a couple years ago) and spark plugs. usually when a coil pack goes, it goes for good, but it's possible these are creating intermittent problems (and they are a known issue, and pretty inexpensive to replace--like $25 a piece from ecstuning)

assuming the car probably hasn't been running well for a while, the cat code could actually be because the cat has been toasted. (my 1.8 ran rich for a long time and killed my cat)

all that being said, the hoses on these cars do get old and brittle and tend to crack so you may have a leak. many times you can spot them visually, but you may have to do a pressure or smoke test.. if the hoses havent been replaced at all, it's a good idea to do it (something like $250 at a dealer but prob much cheaper at an indy shop).

good luck!

Audi Baron

1) how much few is in the tank? i just had an issue where my tank was completely empty but the gauge said 1/4 tank.
2) change your fuel filter. then try starting it. add some fuel.
3) make sure fuel pump is sending fuel. if its is then next step.
4) i would try disconnecting the MAF and trying to start it.
5) check for air and vacuum leaks. and exhaust leaks.
6) i dont think its your coil packs.
7) O2 could be bad. there are not very expensive
8) cat could be bad. very pricey!

cJared3b

Ive replaced all the coil packs and plugs. The fuel filter is new as well. The car is still daily driven. Never sat, broken down.