KYNZ

so i recently posted about a couple seperate issues that ive been having with my 98 A8. Im listing them together now and trying to see if you all know what to do here...aka, what i should ask my mechanic to check out:

1. shaky idle at 550 rpms...feels like a very slight bouncing sensation.

2. strange vibration at 2000-2100 rpms. It is NOT a bent wheel or out of balance tire. it is pretty much instant on at 2k and then by 21-2200rpms it goes away but ONLY at 60mph and 72mph (give or take)...aka 4th and 5th gears.

3. I have been throwing engine misfire codes (P300s) (P0305, 306,307,308). This was after a drive back from Richmond VA this past weekend where about 45miles from home the car's CEL started flashing, then stayed on...then flashed a few more times then stayed on...then it started running REALLY bad. Basically the car was undrivable in 4th and 5th gear and 3rd under 3K rpms. It would stumble and shake really bad. Once into the higher rpms it would smooth out but was still rough running. Also once i got off the highway, the idle was VERY bouncy and the exhaust sounded very burbly (like a quiet flowmaster). HOWEVER, once i got it home, turned it off for a few min, and then restarted...NOTHING. It went away. UGH...this was after sitting in 2 hrs of STOPPED I95 traffic in 106 degree weather.....

I changed my spark plugs to NGK Iridiums the day after (thinking they might be fouled...NOTHING...clean and in perfect condition...except they were Autolites...ew). No code since then but idle is still rough and vibration is still there. I also had my rear diff fluid changed and seals replaced AND my tranny fluid flushed and filter changed. all have not made any of these better....

so, ive spoken with a few people and come up with a few possibilities as to where to look. I am of the mindset that these could all possibly be related. Possiblities to check:

- Compression test on 5-8 - just a check
- Check Timing (if the TB was changed and the timing was not correct this could cause a rough idle?)
- Replace PCV Valve
- Check U Joint (vibration related)
- Check ignition system
- Check Fuel Pressure from the regulator to the injectors
- Clean and/or replace Idle Control Valve

These were some ideas that a friend came up with...unfortunately i am not much of a mechanic but i have a good one...and luckily i still have a little bit of an aftermarket warranty still left to use so its going in in the next day or so...HELP

tonypai

Idle control valve is very easy to clean, three nuts and off it comes.

KYNZ

i saw your response and pic to that in a recent post...i will attack that tomorrow...btw...where is it located in the engine? back near the throttle body?

tonypai

I used some contact cleaner and a rag. Lots of black gunk on the inside and the slide. You'll see what I mean when you take it apart.

My car was stalling when I had the ac on. Once I cleaned it off my problems went away.

Good luck.

Always Overcharged

Have you had your wheels off recently for any reason??

KYNZ

yes, i recently had my CV boot replaced on the LF and i test fitted a set of mercedes rims that ultimately didnt fit...so yeah ive had them off but they are torqued properly and seated right.

Always Overcharged

Hubcentric rings may not have been put back on???

kphani

Can you kindly post a picture with location.. I need to clean her too. Thanks a bunch.

tonypai

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KYNZ

i dont have aftermarket wheels. I have the OEM 17" A8 wheels...which to the best of my knowledge, are already hub centric from the factory. HCRs are only for wheels with a different center bore than the standard OEM Audi center bore. This vibration is NOT wheel related as it ONLY happens at SPECIFIC RPMs and does not fade in and out as you near and pass them. Its ON ...then OFF.