'93 Impreza L wagon, will turn on but will drop rpm under 1K.

It is possible dedicated diagnostic software is needed to restore default values after replacing the throttle sensor.
Just a guess...

Bad spark plug or wire. Observe it while running at night to see if spark is jumping.

may be you should make a diagnostic and you can do it in a garage or you can do it by yourself if you want to do it by yourself you need some tools and you can find some good ones here: chinasinoy.com

Top up coolant, drive 1k and stop. With engine idling check for telltale drops of water under engine and you can locate area of leak.

Fuel? 55-62psi
Oil? 6psig @ 1k rpm, 18psig @ 2k rpm, 24psig @ 4k rpm
Power Steering? 1525psi

If you went 1k miles since that same issue occurred I would look at the transmission. A faulty torque converter, clogged fuel filter, or a clogged CAT can cause a delay in the shifting but it would happen right away not 1k miles later.

sounds like an intake leak / getting to much air at low rpm . spray a (tiny amount) of tractor starter fluid near the intake base and see if the rpm speeds up if it does it's leaking you need new intake gaskets, or a hose is leaking , get a vacum guage to test it.

fuel pressure regulator!! vacuum run not electric!! happened to my 97 lesabre

1st thing to do is have the system tested for the code that caused the check engine light to come, you may also have a fuel pump starting to fail or many other things, the check engine light may be the key. How many wiles on the car?

Hi,

The engine RPM dropping from 1K to 800 when the A/C is turned on would be because the engine is now powering another load, the A/C compressor. However, most designs incorporate a "compensator" that increase the idle back to 1K. This is accomplished with a solenoid coupled to the throttle opening. Electrically, this solenoid is powered in parallel to the A/C compressor. Once energized, the solenoid would open the throttle a little bit more. If your engine has one, then it could either be defective, not electrically connected to the compressor or the reach of the solenoid is not adjusted to push the throttle a little bit more.

Of course, there would be instances where the solenoid is simply installed.

Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards.

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