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post #11 of 13 (permalink) Old 04-07-2008, 08:47 PM
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Audi A4 Erratic Idle

I dumped a ton of money into parts & repairs that didn't work. No one could properly diagnose the issue. I then brought it to an Audi certified specialist who said it was the throttle body / Kombi valve. I put in a brand new throttle body and now it purrs like a kitten.

I spent like $450 for the part and an hour in labor for a total of about $600 or so.

This may be the same issue as you're experiencing but it also could be a host of other issues such as the folllowing. This is the list of things that were done, etc. The only thing that worked was the throttle body. If you've any questions feel free to email me directly at thx. & good luck!

2001 Audi A4 Quattro Avant Wagon (Silver)
1.8 Liter Turbo, Automatic Transmission – Tiptronic
99K miles, Premium Fuel Only, CO License: 880-PUZ

Surging…Rough…Erratic Idle
The vehicle is experiencing erratic idling, especially noticeable at while stopped at stoplights, etc. The tachometer bounces between about ~ 700-1000 RPM and sometimes stabilizes after a few up/down surges; however, the idling is still not as smooth as expected. When shifting into reverse the engine exhibits four or five erratic idles before stabilizing to a more normal level.

It is also noteworthy to mention that when the fan is turned on & off it seems to trigger a momentary increase in erratic idling. In addition, when powering the windows up the RPM’s drop dramatically and lights dim. There are no Check Engine Lights (CEL) displayed at this time.

Possible Causes

* Alternator
* Engine Control Unit – ECU

* Exhaust Gas Recirculation Valve - EGR
* Idle Stabilization Valve
* Inlet manifold (air leak)
* Intake hose (split)
* Sparkplug Wires
* Throttle body butterfly valve -
Carbon deposit build-up
* Throttle body/plate/head
* Throttle Position Sensor (TPS)
* Vacuum hose leak
* Voltage output from battery/alternator

Recent Fixes (2007)

* Air Filter replaced
* Auxiliary Fan Assembly

* Fuel Filter
* Oil Filter
* Engine Coolant Temperature Sensors - ECT
* Applied Fuel Injection Cleaner
* Ignition Coil Packs
* Mass Airflow Sensor – MAF
* Oxygen Sensors: fwd & aft O2 Sensors
* New Sparkplugs

Next Logical Steps

* Check alternator
* Clean or replace throttle body & butterfly valve(i.e. throttle plate); reprogram ECU.
* Check intake manifold & hoses
* Check for vacuum leak
* Check voltage outputs

Originally Posted by powersmokin View Post
I have the same problem with my 1.8t I have been doing a lot of research on this and I am I the middle of doing some repairs and if I figure out the problem I will let you all know the outcome but if anyone out there has any in please let us know thanks.
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post #12 of 13 (permalink) Old 04-08-2008, 10:41 AM
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I will change my Coil pack this evening and let's see.
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post #13 of 13 (permalink) Old 04-09-2008, 08:47 AM
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Rough Idle

I have a 1.8T, 98. At about 65,000 I started putting in non-premium gas. After about a year I started having quite a few issues with the vehicle rough idleing at stops, at times it would even stall at traffic lights. Restarting the car at these times could be difficult.

The Audi garage told me that my spark plugs were really poor and replaced. The car would drive somewhat better for a short period of time but then start the process all over again.

I then started using premium gas and changed the spark plugs again. Three years later I now have 129K miles and it runs smooth, no more cutting out or idle issues. I am not saying this is your problem but for me it was not using premium fuel.
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