Diesel Engine - Poor Throttle Response
23 07 02August 13, 2007
2003575 Supersedes Technical Bulletin Group 23 number 07-01 dated April 5, 2007 due to updated content.
Condition
Vehicle Information
Poor Throttle Response
Poor throttle response on 1.9L TDI equipped vehicle.
Technical Background
Not applicable.
Production Solution
Not applicable.
Service
Tip:
Perform steps 1 through 9; if any of these steps reveals a problem, repair or adjust as necessary and perform a road test to determine whether the customer concern has been resolved prior to continuing on to step 10.
All steps should be documented using VAS 5051 / 5052 printouts.
^ Check Engine Control Module (ECM) ground (GND) connection (see below).
^ Check injection pump timing (see below).
^ heck snow screen (if applicable) at intake air duct (see below).
^ Check vacuum hoses (see below).
^ Check Exhaust Gas Recirculation (EGR) valve and intake manifold air flap - integrated in EGR valve (see below).
^ Check Mass Air-Flow (MAF) sensor and (EGR) valve including solenoid valve (see below).
^ Check crankcase ventilation system (see below).
^ Check engine oil level (see below).
^ Check fuel quality (see below).
1. ECM ground connection, checking
^ Inspect ECM ground (GND) connection for corrosion, poor or no connection.
2. Injection pump timing, checking
^ Check start of injection pump timing (see Repair Group: Diesel direct injection system, servicing)
Tip:
An adjustment to the upper range is advised.
3. Snow screen (if applicable) at intake air duct, checking
^ Check snow screen, located below left front fender in air duct -3-, and clean as necessary.
^ Inspect air cleaner element -1- for proper installation.
If air cleaner element is deformed due to improper installation, this may
cause the MAF sensor to fail.
^ Replace air cleaner element as necessary.
4. Vacuum hoses
^ Check integrity of all vacuum hoses and connections, and repair as needed.
5. EGR valve and intake manifold air flap (integrated in EGR valve), checking
^ Remove intake hose -1- at EGR valve.
^ Remove vacuum hose from EGR valve -2-.
^ Connect hand vacuum pump to EGR valve -2-. See --> Required
Parts and Tools.
^ Apply vacuum and make sure that air flap arrow- opens and closes
freely.
If flap does not open and close freely:
^ Replace EGR valve / flap.
6. MAF sensor and EGR valve including solenoid valve, checking
^ Check correct function of MAF sensor and EGR valve including solenoid valve (see Repair Group for procedure and operation ranges).
Tip:
Since both systems work closely together, if one system malfunctions it will directly affect the function of the other. Therefore it is important to follow the procedure carefully.
^ In addition, the MAF sensor must be full-load tested. See Repair Group 01, On-Board Diagnostic (OBD).
If MAF sensor readings are out of tolerance (even if no MIL ON condition or DTC is present), before replacing any parts (MAF sensor, -G70- or EGR solenoid valve -N18-):
^ Ensure wiring is OK and electrical connections are clean and functioning properly.
If wiring is OK and electrical connections are clean and functioning properly.
^ Replace MAF sensor.
Tip:
For manufacturer defect only: Claim MAF sensor repair/replacement under applicable warranty.
If MAF sensor failed full-load test, and after replacement of MAF sensor full-load value still cannot be attained:
^ Check turbocharger (see appropriate Repair Group).
7. Crankcase ventilation system, checking
^ Inspect and verify that it is functioning to OEM specifications.
8. Engine oil level, checking
^ Check and adjust to proper level if necessary. DO NOT overfill!
9. Fuel quality, checking
^ If condition occurred suddenly, fuel quality may be inferior.
If fuel is suspected to be of poor quality:
^ Drain and refill fuel with known good quality fuel.
10. Carbon build-up, checking
In most cases, performing steps 1 through 9 will restore throttle response.
In some isolated cases, if all previous items are functioning according to specifications and the vehicle still exhibits poor throttle response, it may be necessary to physically inspect the EGR valve and intake manifold as (in higher mileage vehicles) there may be excessive carbon build-up (greater than 10 mm) in the intake manifold and/or EGR valve.
Tip:
While some carbon build-up is normal and not a concern, excessive carbon build-up (greater than 10 mm) is related to fuel quality and soft driving behavior (operation at low speeds and short driving distances, under extremely cold and damp operating conditions.
To inspect for carbon build-up:
^ Remove EGR valve and inspect and record depth of carbon in the valve and intake manifold.
Normally carbon build-up is not a concern; a problem may occur only if it is excessive (greater than 10 mm).
If the carbon layer in the EGR valve and / or intake valve is greater than 10 mm (more than 50% - 60% clogged):
^ Replace EGR valve and / or intake manifold.
If the EGR cooler is clogged more than 50% - 60% in its flow area:
^ Replace EGR cooler.
If new parts are not available, or if it is more economical, the intake manifold and EGR cooler can be cleaned (see below).
Tip:
Prior to cleaning, the intake manifold and EGR cooler must be removed from the engine to ensure that no carbon particles enter the engine.
Warranty
Information only.
Required Parts and Tools
No special parts are required.
Additional Information
All part and service references provided in this Technical Bulletin are subject to change and/or removal.
Always check with your Parts Dept. and Repair Manuals for the latest information.