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Car turns on and idles roughly, press gas let go then stalls? (2004 Honda Civic GX)

I was driving back home the other day and everything seemed fine. Out of nowhere on a stop my car began to shake then it just turned off and wouldn’t turn back on. I was able to make it crank when I turned the key but no luck on getting it started so I had it get towed home.

My brother and I worked on it, and we change the Air Temp Sensor but there was no luck. Today we cleaned the Throttle Body and the Idle Air Control Valve (did not replace them) and still no luck.

The car starts when it’s cold and stays on idle with the idle RPMs moving up and down from 800-650 which makes the idle a bit rough. That wasn’t happening before. So the car will be on when it’s on idle, BUT once I press the gas peddle and then let my foot off the gas peddle the car engine will shake then turn off. I can turn the car back on and keep the gas peddle pressed (reving it) and the car won’t turn off, but as soon as I let go of the gas then the car engine shakes a bit and turns off. No check engine light is on. Anyone have an idea of what it could be or what it is?

I don’t know, but this runs on natural gas, right? That’s important for folks to know.

Most Hondas of that era including the 2004 Civic had chronic transmission failure.Hope its not the problem.

Usually, most cars with bad trans seem to run/idle fine. It’s the moving part that is lacking. On a CNG car, is there a regulator type device?

The problem might with a defective Idle Air Control valve.

One way to check for a bad IAC valve is, while the engine is idling, take the handle of a screwdriver and rap on the IAC valve.

If the idle speed changes it indicates a problem with the IAC valve.


How much is different on intake/control bits on a CNG vs gas motor? Do you have fuel? Have you ever run out of fuel before?