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Discussion Starter #1 (Edited)
I have a 1999.5 Golf TDI which has sat for quite a few years due to a very slight head gasket leak of compression into cooling system - after I drove it home from San Antonio to Houston some 200 miles I notice a bit of coolant coming out of the overflow on way home and when I asked the PO about it and he said - Oh that's the head gasket we put on - it just needs another one - i am thinking OK now wouldn't that have been nice to know before I purchased it - but I don't call people out I just take it as my responsibility to deal with it since I was the one who bought it - my eyes were bigger than my stomach - lol - ok now for the short story - it is hard to start and when it does it just idles - no above idle speeds throwing three codes 17970 - 16485 - 17656 17970 - Quantity Adjuster ( N146) Upper Limit Reached
(intermittent) 16485 - Mass Air Flow Sensor (G70) Implausible Signal 17656 - Injection Start Regulation Control Deviation
(intermittent) I am wondering since it sat and the non beyond idle RPM happened after it sat - maybe something got gummed up in the injection pump? When I have replaced top injection pump O ring gasket I have noticed a variable type sensor - I think it has to do with IQ settings - would that or something else in the upper two top sections of IP that relates to foot feed input need cleaning?
 

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I see the same thread on another VW forum I look after.

VAG Error Code: 17970/005474

EOBD II Error Code: P1562

Fault Location:
Fuel Quantity Adjuster (N146) - Upper Limit Reached

Possible Cause:
Malfunction Indicator Lamp (MIL)(K83) active.
Reduced Power.
Engine jerking.

Fuse(s).
Wiring/Connector(s) from/to Fuel Quantity Adjuster (N146) faulty.
Fuel Quantity Adjuster (N146) not adjusted.
Fuel Quantity Adjuster (N146) blocked/faulty.

Possible Solutions:
Check/Replace Fuse(s).
Check/Replace Wiring/Connector(s) from/to Fuel Quantity Adjuster (N146).
Check/Adjust Fuel Quantity Adjuster (N146).
Check/Replace Injection Pump.

Special Notes:
On the 1.9L ALH TDI engine:
The Fuel Quantity Adjuster (N146) should ohm test between 0.5 and 2.5 Ohms.
With the coolant above 85° C, Measuring Value Blocks (MVB) 001, Field 3 should read between 1.45 to 2.0 Volts.

VAG Error Code: 16485/4794/7330/5667/4795/000257

EOBD II Error Code: P0101

Fault Location:
Mass Air Flow (MAF) Sensor (G70) - Circuit Range/Performance Problem/Implausible Signal

Possible Cause:
Malfunction Indicator Lamp (MIL)(K83) active.
Loss of Power.
Erratic Idle.

Wiring/Connector(s).
Air Leak(s) after Mass Air Flow (MAF) Sensor (G70).
Excessive restrictions in the Intake/Exhaust System.
Dirty air filter, clogged snow screen, clogged CAT.
Mass Air Flow (MAF) Sensor (G70) faulty,
Ground Spots corroded or Paint Residue.

Possible Solutions:
Check/Replace all faulty Wiring/Connector(s).
Check Intake Air Filter.
Check Mass Air Flow (MAF) Sensor (G70).
Check Earth Points.
Read Measuring Value Blocks (MVB).
Mass air flow vs upper threshold model < 60 - 800 kg/h.
Lower threshold model < 0 - 400 kg/h.
Load calculation > 18%.
Fuel system < -17%.

Special Notes:
In MY 1995-2002 (?) in Europe at VW diesel cars Mass Air Flow (MAF) Sensor (G70) had the bad reputation of slowly losing his performance, causing loss of power. It's not a matter of defective or breaking down, but it is filthy / dirty (not easy to clean). You can check functionality by making a log in [01-engine], [Measuring Value Blocks (MVB) - 08], group 003 (3e gear, full throttle, from 1700-4000rpm).
It is not uncommon for a TDI to set Implausible Signal Mass Air Flow Sensor (G70) faults when the engine performance is reduced due to a mechanical problem. These mechanical problems may include, but are not limited to:
Faulty electric fuel pump or Restricted fuel filter. See the Fuel Pump Basic Settings for PD, PPD, and CR TDI Engines page for Basic Settings tips after replacement.
Excessive restrictions in the intake/exhaust system.
Internal camshaft/valve/lifter problems.

Tech Notes:
Before replacing the mass air flow sensor, try replacing the air filter and cleaning the air flow sensor with low compress air or mass air flow sensor cleaner. Reset code and drive vehicle. If the code comes back, it may be necessary to replaced the mass air flow sensor.

When is the code detected?:
A high voltage from the sensor is sent to Engine Control Module (ECM) under light load driving condition.
A low voltage from the sensor is sent to Engine Control Module (ECM).

Description:
The Mass Air Flow (MAF) Sensor (G70) is placed in the stream of intake air. It measures the intake flow rate by measuring a part of the entire intake flow. It consists of a hot film that is supplied with electric current from the Engine Control Module (ECM).

The temperature of the hot film is controlled by the Engine Control Module (ECM) a certain amount. The heat generated by the hot film is reduced as the intake air flows around it. The more air, the greater the heat loss. Therefore, the Engine Control Module (ECM) must supply more electric current to maintain the temperature of the hot film as air flow increases. The Engine Control Module (ECM) detects the air flow by means of this current change.

As taken from my new Free EOBD II Error Codes software
 
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If Keith's suggestions don't work I would also look over all your wiring. You said it's been sitting and I had an issue with my 06 BEW when it sat for awhile. I had a mouse make its home in the engine compartment and chewed up a bunch of my wiring which caused me all kinds of electrical nightmares getting it back on the road again.
 

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My 99.5 had a bad wire in the bundle under the battery, near the starter. That code points to the injection pump, so you want to rule out the simple stuff. Similar with the MAF code, often the plugs get iffy.
 

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03 Jetta. Nothing special. 380k miles
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I have an 03. Similar symptoms but not as severe. My problem was VERY restricted intake manifold. First verify it’s not plugged exhaust. Shop vac. I had to remove the intake manifold to verify it was plugged. Took me about 6 hours of soaking in SuperClean degreaser (I think it is mostly lye?) and manually scraping with an old steel tent stake. I got most of a pint of black fluffy nasty out of it. I’ve put about 120k on it since then with no recurrence. Almost all highway including hills. Good luck!
 
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