1990 Volkswagen Other Repair Question
Cabriolet engine miss once warm
1990 Cabriolet 4 cyl Front Wheel Drive
Manual 95000 miles
I believe I caused this problem. After cleaning the intake/injector rail area to find an oil leak the car runs poorly once warm. After first starting it is fine. Once it hits running temp it runs rough at idle, smells like it is over fueling, spark plugs are damp and carboned (were not before this) It won't run over 2800 rpms under load. Accelerates poorly and lurches. If I unplug the coolant sender to the computer it doesn't idle as well but runs normal. Good power and no miss. The coolant sender Ohms appear to be close to spec. 200 ohm at normal temp. I also cleaned the throttle body area before this started.
You may have created the problem, and I think you are somewhat on the right track with the engine coolant sensor as this would definetely have an adverse affect on warm running. Have you taken a look at the fuel regulator? You will not need all the fuel delivered to the engine, thus some/most returns to the tank, as well, we have more than enough flow and pressure, (two different things). The pressure regulator will look at throttle position (through engine vacuum) and either by-pass fuel back to the tank, or allow it be sent to the injectors. Think of kinking a garden hose and how this affects the flow, pressure and delivery. You will probably find the pressure regulator at the "end" of the fuel rail. ensure that the vacuum line is in good shape. Check your vacuum schematic to see when you "should" be recieving vacuum to this device. An inexpensive fuel pressure gauge "tapped" into the fuel rail should give you a better clue if the regulator is working properly or at all.
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