Car misfiring and the engine wiring loom needs to be replaced

check for sure the batt and charging.that can cause lots off problem.
weak batt gifs weak spark charge chould be round 14.7 not 14.9
that toomuch also not good.check sparkplug wires and rotor,if needed,
to replace use original parts.check also pipes off the turbo.

When replacing wiring looms it is best to tag all wires first and un-plug and plug as you go. To have an auto electrician do it will be costly. Arm yourself with a workshop manual before you start as it will be the best help you will get.

02 Audi TT with a 1.8L turbo or none turbo engine, Audi recommends, timing belt replacement every 105,000 miles.You still got some time, hope this was very helpful.

It is probably either the N75 valve(Diverter Valve) or the wastegate actuator. Usually a significant boost leak will set a DTC, still check all hoses and clamps.

A bad wastegate actuator or flap would cause no boost but not necessarily the air-sound.

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Testing N75

Air Bypass Valve: Testing and Inspection
With Generic Scan Tool
Wastegate Bypass Regulator Valve, Checking
Recommended special tools and equipment e.g.:
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
Test sequence
- Switch ignition off.
- Disconnect connector at solenoid valve for boost pressure regulation.
- Measure resistance between terminals of valve.
Specified value: 25...35 Ohm
If specified value is not obtained:
- Replace Wastegate Bypass Regulator Valve -N75-.

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Testing N249

Exhaust Bypass Valve: Testing and Inspection
With Generic Scan Tool
Recirculating Valve For Turbocharger, Checking
NOTE: Valve opens between connection to intake manifold and connection to deceleration shut-off valve with no voltage. Connection to vacuum
reservoir is closed.
Test sequence
- Switch ignition off.
- Disconnect connector from Recirculating valve for turbocharger -N249-.

- Measure resistance between terminals of valve.
Specified value: 27...30 Ohm
If specified value is not obtained:
- Replace Recirculating valve for turbocharger -N249-.
If specified values are obtained:
- Connect test box to control module wiring harness, connect test box for wiring test.

- Check wire between test box socket 105+2-pin connector terminal 2 for open circuit according to wiring diagram.
Wire resistance: max: 1.5 Ohm
- Also check the wire for short circuit to B+ and Ground (GND).
If no malfunctions are found in wire:
- Check wire between 2-pin connector terminal 1 and the Fuel Pump (FP) Relay -J17- for open circuit according to wiring diagram.
Wire resistance: max: 1.5 Ohm
If no malfunctions are found in wires:
- Replace Engine Control Module (ECM).

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To test the wastegate, locate the wastegate linkage rod and verify that there is no play and that it is closed. You can apply compressed air to the actuator to see if it opens and closes. (not more than 30 psi)

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Vehicle: Vacuum and Vapor Hose Diagrams
System Diagram
Vacuum Diagram
1 From fuel tank
2 EVAP canister
- with Evaporative Emission (EVAP) Canister Purge Regulator Valve -N80-
3 Check-valve for EVAP canister
- Between EVAP canister and intake manifold before turbocharger Installation position (light/dark side): Arrow points in direction of flow, as
shown
4 Turbocharger
5 Pressure unit for boost pressure regulation
6 Mechanical recirculation valve
7 Brake booster
8 Check-valve
- Between brake booster and intake manifold
- Installation position (light/dark side): Arrow points in direction of flow, as shown
9 Wastegate bypass regulator valve -N75-
10 Mass Air Flow (MAF) sensor -G70-
11 Air cleaner housing
12 Pressure control valve for crankshaft housing ventilation
13 Vacuum reservoir
- Bolted on at cylinder head
14 Charge air cooler
- With charge air pressure sensor -G31-
15 Fuel pressure regulator
16 Throttle valve control module -J338-
17 Intake manifold
- With Intake Air Temperature (IAT) sensor -G42-
18 Crankcase ventilation
19 Check-valve
- Installation position (light/dark side): Arrow points in direction of flow, as shown
20 Recirculating valve for turbocharger -N249-
- Component location Fig. 1
21 Check-valve
- Between EVAP canister and intake manifold
- Installation position (light/dark side): Arrow points in direction of flow, as shown
22 Charge air cooler

check for deformed tyres ?? this is the most obvious cause,i may be old dinasaur who gets lost with sensors and electronic stuff but after 40 yrs somethings never change

change the mass air flow meter.

First check spark plugs/wires/distributor cap (tune up). Also would be good idea to use fuel injector cleane and change fuel filter and O2 sensor.
Hope that helps
Good Luck

replace the speed idle sensor

possible air flow meter,or vains sticking in turbo (if its a pd engine)check your air flow rate on vag tool,should be between 12 - 14 kg/hr or 2-4 g/s

Clean the throttle body and reset the idle. Also check the O2 sensor. I am having the same problem with my 01 tt