Car keeps stalling

Most mechanics have scanners that can record a snapshot of sensor data when a problem occurs. You may need to go to a VW dealer because Volkswagen likes to do things differently than most other manufacturers. Your mechanic will have to drive the car until the problem occurs, then he presses the "record" button. Because the data passes through the scanner's memory, the recording actually starts a few seconds before you press the button. That data can be replayed slowly later to see what happened. The hard part sometimes, when a sensor's signal has a problem, is determining if that is what caused the stalling or if that signal was in response to the non-running engine.

Chrysler also has a special scanner used as a "flight recorder" that they leave in the car with you, then you press the button when the engine stalls. I know some other manufacturers have that too but I'm not familiar with using them.

There should also be diagnostic fault codes set related to the stalling if it is the result of a sensor problem. Usually the fuel supply system is not monitored so that would be the place to start looking if there's no fault codes.

Since you can restart the engine right away, you could also have nothing more than a low idle speed. Observe if you get a nice "idle flare-up" to 1500 rpm when you start the engine. If you do not, the Engine Computer is not controlling idle speed.

Look at the fresh air tube between the mass air flow sensor and the throttle body. If there's a leak that allows outside air to enter the engine without going through the mass air flow sensor, that air won't get measured and the computer won't command enough fuel to go with it. If the engine rocks when coasting, it can tug on hoses and wiring harnesses and cause intermittent problems.

https://www.2carpros.com/articles/replace-an-air-intake-boot

Thanks for the reply. There's more to the story though because this can happen to any car. The pickup for the fuel pump lies on the bottom of the tank, so if sludge was blocking it, the fuel level would not be a factor. The more common cause is using ethanol in the gas. Mold grows on that alcohol and it can plug the pickup screen. I've had to replace those screens three times on two cars. They become plugged about every 200,000 miles. When you have an engine that uses a fuel pressure regulator on the fuel rail on the engine, the clue is the stalling occurs after the first ten to fifteen miles of driving, and when the highest volume of fuel is being pumped, ... Which is during coasting. The flow draws the mold in the tank to the screen and blocks it. The second clue is if you wait for about five minutes, the blockage will clear up enough for the engine to run fine for another mile or two. In my cases, the second vehicle this happened to had fuel injection. Once I figured out what was causing the stalling, the additional clue was to disconnect the vacuum hose at the fuel pressure regulator, and plug it. That caused pressure to be too high, but it greatly reduced the amount of fuel being pumped. The only fuel that had to make it through the screen was what the engine was using. That is far less that what is normally flowing.

A similar problem occurred on Chrysler products, but it affected their fuel pumps. Their pumps are uncommonly quiet, but that is because they are built to very close tolerances and clearances. The mold, and other debris, causes the rotor to lock up. The dead pump causes a crank / no-start. People replace the pump four or five times over a period of months with ones from an auto parts store, then get frustrated and buy one from the dealer's parts department, then never have another problem. Their assumption was the aftermarket pumps are junk, but that is not the case. Each replacement pump collects some of that debris, and by the time the Chrysler pump is installed, there's no gunk left to lock up that one. Also, if you buy a replacement pump from NAPA, (and probably from some other stores), you're getting the same pump as from the dealer. Some of the auto parts stores get their pumps from the same suppliers that sold them to Chrysler.

The proper fix, when you know about it, is to have the tank steam-cleaned at a radiator repair shop, and replace the pickup screen when a new pump is needed.

Also, most fuel pumps sit inside a little bowl in the middle of the tank. That insures the engine won't stall from lack of fuel when going around a corner and fuel runs away from the pickup. The pickup is always sitting in about five inches of gas, even when the tank is almost empty, and more when the level is higher than that bowl. The only thing that might cause fuel level to be a factor is the debris suspended in it will be more concentrated and more likely to fully block the screen.

One of the engine sensors may be faulty go get a scan first and check for any unresolved fault codes, this should show a sensor fault if one is causing your problem.

Might be the throttle valve control mod, this is 1.8 engine shown, others are similar.

EPC. That is your check engine light (malfunction indicator light)and you will need to use an OBD-II code reader to read the code. AutoZone will loan you a code reader for free.

Get some carburetor cleaner and spray down the throttle plates and intake. Then check the idle it may be too low you will need to adjust the idle higher to stop this.

New purge valves can be bad out of the box. The only way fuel vapors will enter the intake manifold during fueling, is if the N80
is sticking open. Have it checked again.

Thomas

Hi,

The engine's idle speed is controlled by the throttle body control module. In this case, we need to first make sure the throttle body is clean. Take a look through this link it explains how to service one:

https://www.2carpros.com/articles/throttle-actuator-service

If that is clean, then we need to check the throttle valve control module. Here are the directions for testing. This does require a scan tool to complete and is a bit complicated. However, if you have questions, let me know. All attached pics correlate with these tests.

__________________________

2000 Volkswagen New Beetle (1C1) L4-1.8L Turbo (APH)
With Generic Scan Tool
Vehicle Powertrain Management Relays and Modules - Powertrain Management Relays and Modules - Computers and Control Systems Electronic Throttle Control Module Testing and Inspection Component Tests and General Diagnostics Throttle Valve Control Module J338, Checking With Generic Scan Tool
WITH GENERIC SCAN TOOL
Throttle Valve Control Module, Checking

NOTE: Use only gold-plated terminals when servicing terminals in harness connector of throttle valve control module.

Function
The throttle valve activation occurs via an electric motor (throttle drive) in the throttle valve control module. It is activated by the Engine Control Module (ECM) according to specifications of the two sensors, Throttle Position (TP) Sensor -G79- and Sender -2- for accelerator pedal position -G185-, function of the E-gas system.

Components of Throttle Valve Control Module -J338-:
- Throttle drive (power accelerator actuation) -G186-
- Angle sensor -1- for throttle drive (power accelerator actuation) -G187-
- Angle sensor -2- for throttle drive (power accelerator actuation) -G188-

Recommended special tools and equipment
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram

Test requirements

pic 1

- The respective fuses of Motronic Engine Control Module (ECM) -J220- must be OK.
- Battery voltage must be at least 11.5 volts.
- All electrical consumers such as, for example, lights and rear window defroster must be switched off.
- Parking brake must be engaged or else daylight driving lights will be switched on.
- If vehicle is equipped with an A/C system, it must be switched off.
- Ground (GND) connections between engine and chassis must be OK.
- Throttle valve must not be damaged or dirty.
- Coolant temperature must be at least 80 degrees C, Diagnostic mode 1: Check measuring values; PID 5, Coolant temperature.

Function test
- Connect diagnostic tester. See: Computers and Control Systems > Reading and Clearing Diagnostic Trouble Codes > Diagnostic Tester, Connecting
- Switch ignition on.
- Under address word 33, select "Diagnostic mode 1: Checking measured values."
- Select the measuring value "PID 17: Throttle valve position (absolute)."
- Check specified value of throttle valve position (absolute) at idle stop:

pic 2

- Slowly depress accelerator pedal up to Wide Open Throttle (WOT) stop while observing the percentage display.

The percentage display must increase uniformly.

- Check specified value of throttle valve position (absolute) at Wide Open Throttle (WOT) stop:

pic 3

- End diagnosis and switch ignition off.

If specified values are not obtained:

Check resistance
- Connect test box to control module wiring harness, connect test box for wiring test. Engine Control Module (ECM) is not connected.
- Measure resistance of throttle valve drive between test box sockets 117 +118
Specified value: 1...5 ohms

If specified value is not obtained:
- Replace Throttle Valve Control Module -J338-, item 20
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code. See: Computers and Control Systems > Monitors, Trips, Drive Cycles and Readiness Codes

If specified value is obtained:
- Check voltage supply of throttle valve control module and wiring to control module.
- Check Throttle Position (TP) Sensor -G79- and Sender -2- for accelerator pedal position -G185-.

If voltage supply and wires are OK:
- Replace Motronic Engine Control Module (ECM) -J220-.

Checking voltage supply and wiring to control module

pic 4

- Disconnect 6-pin connector -2- at the throttle valve control module -1-.

pic 5

- Connect multimeter to terminals 2 + 6 of connector for voltage measurement.
- Switch ignition on.
Specified value: at least 4.5 V
- Switch ignition off.

pic 6

- Connect multimeter to terminal 2 of connector and Ground (GND) for voltage measurement.
- Switch ignition on.
Specified value: at least 4.5 V
- Switch ignition off.
- Connect test box to control module wiring harness, connect test box for wiring test.

Engine Control Module (ECM) is not connected.

pic 7

- Check wires between test box and 6-pin connector for open circuit according to wiring diagram:
Terminal 1 + socket 92
Terminal 2 + socket 83
Terminal 3 + socket 117
Terminal 4 + socket 84
Terminal 5 + socket 118
Terminal 6 + socket 91
Wire resistance: max. 1.5 ohms

- Also check wires for short circuit to each other.
Specified value: Infinite Ohms

If no malfunctions are found in wires:
- Check voltage supply of Engine Control Module ECM). See: Engine Control Module > Component Tests and General Diagnostics > ECM Voltage Supply, Checking
- Erase DTC memory of Engine Control Module ECM), Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code. See: Computers and Control Systems > Monitors, Trips, Drive Cycles and Readiness Codes

_____________________________________________

Let me know what you find or if you have other questions.

Take care,
Joe