1991 VW Vanagon GL Idle Issue While Engine Hot

[vangogh79]

Hi all,
I’ve recently purchased a 1991 Vanagon 2.1L GL. I’m having a peculiar issue with the idle and wanted to see if anyone else had experienced the same symptom or can point me in the right direction.

When my engine is cold and I start it, it idles at 1000 RPM steadily. The engine runs smooth, with no misfires or shaking. There are no fluctuations in the RPM either. I let the car sit for 5 minutes and once the temperature gauge reaches about halfway, I take it for a drive. At this point, the engine is hot.

When the van is put into Drive, the RPM drops slightly, one tick below the 1000 mark. It drives perfectly fine until I have to come to a complete stop. If I stop for 10 seconds, the RPM drops to 500 and then the engine turns off. After turning it on again, the RPM goes to 1000, I put it in Drive and it drops one tick below 1000 and I’m able to drive it until the next stop. This cycle repeats over and over.

As soon as I come to a stop, if I put the van into Neutral, the RPM stays at 1000, and the engine doesn’t turn off. But as soon as I put the van into Drive again from Neutral while stopped, if I don’t push the gas and take off, the engine will turn off.

After coming to a complete stop while the engine is in Drive, if I simply take my foot off the brake and not gas it, the van will also turn off. I must push the gas pedal to prevent the engine from turning off. It’s like, I cannot come to a full stop while in Drive mode with a hot engine.

What could be causing this?

Here’s what I’ve done so far:

1. I have the Bentley manual and I’m reading pages 24.23.
2. The gas tank has been cleaned, and it’s filled with gasoline. No leaks or smell of gasoline.
3. Oil was recently changed (20w50).
4. The fuel pump and the fuel filter were replaced recently. Both are functioning.
5. The Idle Air Control Valve was disassembled, connected to a 12v battery and confirmed that the valve opens and closes without any air leaks. The unit was not replaced since it's functioning.
6. I’ve inspected the Idle Stabilizer Control Unit circuit board and did not see any burnouts. The unit was not replaced.
7. The idle switch makes a clicking noise when moving from the rest position and when in full throttle position.
8. There are no cracks in the air intake boot. It’s been cleaned along with the throttle body.

Could the oxygen sensor or the temperature sensor be faulty? Fuel/Air mixture screw? Anyone experienced anything like this?

Thank you for any help or advice.

Bobby

[Altoona]

Just dealt with a similar issue and the culprit ended up being the coil. Van drove perfectly but would hiccup and occasionally stall at idle. Didn't expect it to be the coil but that's what fixed it.

[vangogh79]

[xflyer]

Need to check all the usual suspects: Compression, valve adjustment, timing, air leaks (injector seals, hoses, manifold to head gasket, fix any exhaust leaks, and check spark quality.
Spark should jump from fat coil lead to ground at least 10-12mm and be blue/white. If spark is red/orange and is 5-6mm or less; check ignition system wiring including grounds. Worst case is a failing ECU. The ignition circuit in the ECU is the first thing to fail and it can get worse over time.
Also set base idle speed per the Bentley. And check that the throttle is closing at idle. Sometimes the stop screw has been fiddled with.
The Idle Stabilizer unit can be checked with a timing light. With the engine idling the timing should move around a bit. This is to try to keep the engine at 850-950 rpm. If the basic idle settings and timing are off the system will not work properly.
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1989 Campmobile, 1984 7 passenger beater Vanagon
Both with cool A/C