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My car turns off while I'm driving

I will be driving my car and it will turn off - I lose power breaks and steering but all my electrical lights, dash lights still work. This happens most often when I’m coasting but can happen while my foot is on the gas. Usually, I just pull over and start it up again, although it can take a few tries (which never happens when I cold start it).

I’ve had 2 shops look at it, but since it doesn’t happen when they drive it it’s hard to diagnose. I’ve had the battery, spark plugs, and radiator replaced within the last 18 months. I do regular scheduled maintenance and the car is in good condition otherwise.

Also, when my car is in park the idle is high ~ 2000 rpms, but in drive or neutral the idle can drop to ~700 prms. Is the idle the problem? Fuel pump? A sensor or something? I’m sick of paying useless diagnostic fees and repairs that don’t fix my problem.

What kind of car do you drive? Year, make, model, and engine type, etc, please. This information will help.

Does the check engine light come on when the engine stalls? Does it stay on afterward? Have the mechanics who looked at the car done anything other than look?

I think the high idle speed could easily be connected to the stalling problem. 700 is not terribly low for a normal idle. 700-750 is about where most cars should idle, but 2000 in park or neutral is way to high.

I would ask someone to test and/or clean the idle air control (IAC) valve. This valve controls idle speed on most modern, fuel-injected cars, which I assume you have. Sometimes cleaning the valve helps, other times the valve must be replaced.

There could be other causes, but the IAC valve is a good place to start.

1991 Volvo 740 (no turbo) 4 cylinder engine, automatic

Mechanics have cleaned the intake, checked the O2 sensor, replaced battery and spark plugs, replaced water pump, radiator and hoses, timing belt, tensioner… I’ve had quite a bit of work done since buying it in Jan 2005.

The check engine light will come on for less than one minute and turn off. The mechanics told me that that is normal.

The problem may be due to an intermittent relay that supplies power to the ignition area. I think there are some relays under the panel near the windshield, under the hood.

Here are the instructions for testing the idle air control valve. Download and print these instructions for your “mechanics”:
If the mpg is poor, I suspect the engine coolant temperature (ect) sensor as being faulty (and of causing hard starts). The tests of the ect sensor are simple for a mechanic with a multimeter and knowledge in use thereof. If in doubt, change it out.