Attachment Bulletin # 240303
Group: 24Number: 03-03
Date: Nov. 6, 2003
Subject:
Engine, Fluctuating Idle or Idle Speed Too Low
Model(s):
A4, Cabriolet, with (Eng. cod. AMB, ATW, AWM)
TT, with (Eng. code AMU, ATC, AWP, BEA) 2000 --> 2003
Supersedes T.B. Group 24 No. 03-01 dated Aug. 5, 2003 due to procedure revisions (marked by asterisks)
Condition
1.8L 5V Turbo Engine idle fluctuates or is too low at times, poor throttle response, engine bucking, cold start driving concerns, MIL ON.
May be caused by contaminants (dirt, oil) on interior surfaces of throttle valve control module -J338-.
Contaminants may cause bucking due to wrong airflow recognition.
DTC's which may be associated with condition:
In conjunction with the above listed DTCs, the following DTC's which may also be stored:
Service
Always review and follow Cautions and Warnings listed in the Repair Manual regarding the use of the VAS 5051 and VAS 5052 during any road test.
A4, Cabriolet and TT models:
Using a second Technician, road test vehicle with VAS 5051 or VAS 5052 connected:
- Select "Vehicle Self Diagnosis mode".
- Select vehicle system "01 - Engine electronics".
- Select Diagnosis Function "04 - Basic settings.
- Input "032" on keypad to select "Display group 032"
- Select "Q", button to confirm.
- Drive approx. 10 miles (15 kilometers) under normal driving conditions.
Channel 1 value (at idle) should be:
^ approx. +/- 2.5%
Channel 2 value (at partial load) should be:
^ Approx. +/- 10% (A4)
^ -2% to +8% (TT m.y. 2000).
^ -10% to 0% (TT from my. 2001)
- If channel 2 value is:
^ Above +10% (A4)
^ Above 8% (TT m.y. 2000)
^ Above 0% (TT from m.y. 2001)
** These values indicate that the system is leaner than normal.
- Check for air leaks in air duct before turbocharger using VAG 1687 Diagnostic Tool as outlined in Technical Bulletin Group 01 Number 01-01 dated Oct. 26, 2001.
- Check Mass Airflow Sensor -G70- **
If channel 2 value is:
^ Below -10% (e.g. -15%) (A4)
^ Below -2% for (TT m.y. 2000)
^ Below -10% (TT from my. 2001) These values indicate system is richer than normal (due to the engine getting less air than measured by the MAF sensor)
- Check for air leaks in pressure side air duct using VAG 1687 Diagnostic Tool as outlined in Technical Bulletin Group 01 Number 01-01 dated Oct. 26, 2001.
If values in Display group "032" are within limits:
^ Lambda adaptation and Mass Air Flow (MAF) sensor are OK
TT models only:
- Select the <-- button.
- Input "115" on keypad to select "Display group 115".
- Select "Q" button to confirm.
- Check Channels 3 and 4 of Display group "115" at full load acceleration in 3rd gear at 2000 RPM. Here the following can be seen:
^ Channel 3 value = Target value of boost pressure according to programmed map in ECM.
^ Channel 4 value = Actual existing value of boost pressure.
^ Values should not deviate from each other by more than 50 mbar.
If values deviate (consistently) more than 50 mbar:
- Check Charge air pressure system (see Repair Manual Group 21 - Turbocharger, G - Charger).
A4, Cabriolet and TT models:
After road test:
- Let warm engine idle in warm surrounding.
- Switch OFF ALL consumers (A/C, seat heating, window defroster, etc.).
- Select the button.
- Input "003" on keypad to select "Display group 003".
- Select "Q" button to confirm.
^ RPM, Air mass, throttle valve angle and the Advance angle are displayed.
If Channel 3 value (throttle valve angle) is at 2% or higher:
- Clean throttle valve control module -J338- (see cleaning instructions below) thoroughly and readapt.
- Inspect crankcase ventilation system hoses. If sludge or oil deposits are found inside hoses:
- Clean inside of hoses as necessary.
** For vehicles up to and including M.Y 2002 only: **
- Remove suction jet pump for brake booster (arrow).
^ Arrow indicates airflow direction (towards intake manifold).
- Inspect suction jet pump (in area of white circle) for blockage.
If blocked:
- Replace suction jet pump.
Continued for ALL vehicles: **
Throttle valve control module -J338-,
Cleaning instructions:
- Remove intake boot from throttle valve control module.
- Inspect interior surface of throttle valve control module and throttle plate for dirt / oil film.
If interior of throttle valve control module is not dirty:
- Reinstall intake boot.
- Continue with diagnosis, (see appropriate Repair Manual group or VAS 5051 Guided Fault Finding).
If interior of throttle valve control module is dirty/oily:
DO NOT replace throttle valve control module for this condition. Over a long period of time it is possible that dirt can accumulate on the inner surfaces.
- Clean interior surfaces of throttle valve control module (on both sides of throttle plate) with a soft clean cloth.
Note:
It is not necessary to remove the throttle valve control module -J338- to clean.
- For heavier deposits of dirt / oil film, apply Wynn's(R) X-Trend(R) V.I.C. Combustion Chamber Cleaner: Part No: 61510 (U.S.), Part No: 61512 (Can.) on a soft clean cloth then, clean interior surfaces using this cloth (one can of cleaner will do many vehicles, therefore it is considered shop supply)
- Reinstall intake boot.
- Perform throttle valve control module adaptation (see Repair group 24 of appropriate Repair Manual).
If throttle valve control module adaptation cannot be performed after several attempts (see Repair group 24 of appropriate Repair Manual for proper adaptation conditions):
- Replace throttle valve control module.