05 A4 1.8T mis fire at idle

[drod]

In november @ 96K miles car started mis firing and shaking CEL flashing. Changed all 4 coil packs and plugs. Still mis firing brought it to a "profesional" found 2 vacume leaks. Replaced the broken tubes/lines car ran fine untill about 1 month ago (104K). CEL would come on if car was started and left idle for a few mins. If I reset the CEL it would not come back on unless I would leave it idle for a few mins. Therfore no mis fires or CEL comming on if the car was placed in drive and took off right after starting. The CEL codes detected by OBD II reader at autozone would be P0301, P0302. P0303 and P0304. I drove the car this way for untill now (115K). Ticking noise comming from alternator. Brought car to "professional" to diagnose the noise and the mis fires. Professional replaced alternator and throttle body $1200 later. Picked up the car noise was gone but misfires are back at idle with the same codes. Returned the car to the "profesional". Then diaganosed it as the MAF sensor which he was calling the air meter (same thing?). Replaced the MAF and car still has same symptoms. 1 thing i did notice is that it only seems to happen at idle with the AC on. Coincidence?

Someone please help!! going crazy.

Also what tool should I buy for trouble shooting? OBD II or the "vag-com" thing I keep reading about. Is it software that runs on a PC or is it hardware and software.

[imnuts]

VCDS/vag-com is software, but Ross-Tech (company that makes it) also sells a cable as well. The cable has built in authentication to enable full functionality, otherwise, you can use a generic OBD2 cable and buy a license key for the software to enable full functionality.

If it is misfiring on all cylinders, I would start out by checking anything and everything related to ignition. Spark plugs, coils, wiring harness, and all the vacuum lines. Look for anything out of the ordinary like cracked and broken lines, exposed wires, etc. If someone already replaced some vacuum lines, odds are that there are others that could be on their way out as well.

[awdjunkies]

If you've replaced all the culprits and still have the p01/2/3/4 codes, it could be as easy as an o2 sensor/cat, or the wiring CP harness. Did you check the harness/connectors when you replaced all the CPs + plugs? Are you sure he fixed all the vacuum leaks?


Every Audi/VW owner should invest in a Vag Com. This is an invaluable tool which gives you information that you wouldn't normally get with a generic OBDII Reader.

When was the last time you replaced the fuel filter? were the plugs gapped correctly? when did you do the timing belt/water pump service?


Welcome to Audizine.

[drod]

Water pump and timming belt were replaced at 45k by the dealer then pump was replaced again at 56k. I have never replaced the fuel filter. I didn't check the cp wiring. Also I never checked the gapping for the plugs. Was told they were pre gapped. I did a visual exam of the vaca lines but not very thorough. Is ther a systematic way to test them or is it just visually examine them.i.e is there a test that can be performed on them?

[frei0623]

I would go with the spark plugs on this one for $5,000.....

Had the same problem last year with mine. Make sure that they are gaped. I never trust them when they say they are pre-gaped.... Its like saying raw chicken is good for you....

[drod]

Plug gaps were good. Changed fuel filter.. Made no difference.. After I changed the throttle body car aeed to run worse. Would see the cel flash at idle.. Does the throttle body need to be programmed on the B6? I'm giving up and bringing it to the stealership..

[smppro]

my 1.8t was giving me lots of misfire codes then TB codes so i replaced the entire engine bay wiring harness for $150 and never had a problem again. Plus you should be taking your car to a VW/Audi specialist that uses a vag com and is familiar with the problems these cars have otherwise people are just throwing parts at it because they dont know any better.

[diagnosticator]

In november @ 96K miles car started mis firing and shaking CEL flashing. Changed all 4 coil packs and plugs. Still mis firing brought it to a "professional" found 2 vacume leaks. Replaced the broken tubes/lines car ran fine untill about 1 month ago (104K). CEL would come on if car was started and left idle for a few mins. If I reset the CEL it would not come back on unless I would leave it idle for a few mins. Therfore no mis fires or CEL comming on if the car was placed in drive and took off right after starting. The CEL codes detected by OBD II reader at autozone would be P0301, P0302. P0303 and P0304. I drove the car this way for untill now (115K). Ticking noise comming from alternator. Brought car to "professional" to diagnose the noise and the mis fires. Professional replaced alternator and throttle body $1200 later. Picked up the car noise was gone but misfires are back at idle with the same codes. Returned the car to the "profesional". Then diaganosed it as the MAF sensor which he was calling the air meter (same thing?). Replaced the MAF and car still has same symptoms. 1 thing i did notice is that it only seems to happen at idle with the AC on. Coincidence?

Someone please help!! going crazy.

Also what tool should I buy for trouble shooting? OBD II or the "vag-com" thing I keep reading about. Is it software that runs on a PC or is it hardware and software.

What are the EXACT DTC codes that are stored? It's normal for a Tip trans car to vibrate more at idle speed with Drive engaged, with the A/C system ON in AUTO mode, and working hard with the engine cold after start up. Sounds like the "Professional" is guessing and throwing expensive parts at the problem however. VCDS (VAG-COM,) is comprised of a genuine Ross-Tech OBDII interface cable, and Software that runs on a laptop PC. VCDS provides Audi/VW Group diagnostics capabilities and information similar to the dealer tools. Cheaper OBDII scan tools only provide generic DTC information.

[drod]

Thanks everyone for the help. Throttle body needed to be programmed.