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Engine Shuts Off?

I have a 1993 Cadillac STS which I just purchased with low miles and clean carfax. Local car. Everything works like a dream and drives beautiful. All of the sudden it just shuts off ()Northstar engine()and I have to place it in park and start it again. It usually just happens on slow traffic. No engine service light so I can’t get the auto shop to get me an error code. Anyone know what it might be?

The ignition switch (the electrical component, not the lock cylinder) should be a major suspect at this point, particularly if the car was previously driven by a woman who had MANY keys as well as various do-dads on her key ring. I am constantly fascinated/appalled by women whose key rings bear more weight than my wallet.

Excess weight on a key ring can wreak considerable damage on an ignition switch.

This would cuase the car to just shut off?

This would cuase the car to just shut off? It can. It can become erratic.

It can, indeed.

Can you ask Myra, or Cynthia, or whatever her name might be, to weigh her key ring?
If she needs an industrial scale for this task, then you have found the likely culprit.

currently only three keys and the alarm remote on it…doesn’t feel heavy…is there a fix for this problem?

No matter what YOU have on the key ring, the person(s) who owned this car for the previous 17 years have left their imprint on the car and its components. When you buy a car that is this old, you will experience the fallout of the bad behaviors of all of the people who drove it prior to you, and in 17 years, that could be a whole heap of brain-dead people.

Is there a fix for this problem?
Yes, and it could involve replacing the ignition switch.
But, it is best to have a competent mechanic diagnose the problem, rather than those of us who are communicating from cyberspace.

I hope that you have hard copies of this car’s complete maintenance history.
If not, you have to assume that no maintenance has been done for X number of years.

It is time to get out the GM Maintenance Schedule, compare that to whatever maintenance records you might have, and prepare to do lots of catch-up maintenance–unless you can confirm that it has already been done!

It might just be it! I just realized the similarity of keychain movement when it shuts off…It happens when I take off in a hurry and start it up…maybe the chip in the key moves when the key chain moves back and forth! Thank you!!!

The igntion switch is much more likely to be the source of the problem, rather than the chip in the key.

ok, I will be careful when I start it in the meantime…do you know if this is easy to fix?

Does the shut off only occur with your foot off the gas? Does it feel like it wouldn’t shut off if you were pressing the accelerator slightly?

It also occurs as I am driving with my foot on the accelerator.

Does it seem to shut down as if you literally shut the key off? Do you have dash lights during the shutting down phase? WHen the engine is off after shutdown do you hear your fuel pump hissing in the back of the car? what do you do to restart? simply turn the key again? DOes it start right up again?

Start the car and monkey around with the key in the ignition…can you wiggle it or turn it any way that affects a shutdown. Could very well be an ignition issue…could be a security issue as well…such as the passkey chip losing contact w the transmitter…there are wire-arounds for this if it becomes an issue…I used to have to wire around them when doing remote start systems in these cars.

The ignition switch itself is suspect…check it by monkeying with the key while running… Fully describe the shutdown…is it like running out of gas…like a slow stumble and shutdown slowly or is it like whacking the ignition off?

It does not shut down if I wiggle the ignition. And yes it 99% of the time starts up right after it shutss off. Sometimes I have to try it twice but it always shutss off. When it shutss off I amd driving slow or am at a stop and it flutters a little (I can see the rpms go up and down) and then it shuts off. Sometimes the rpms go down then back up. When I am driving faster it will do this fluttering but it keeps going because I will accelerate a little. It is almost like it has a hick-up.I changed the fuel filter right before it did this and am wondering if they installed it wrong? The funny thing is it will work fine for hours and hours and then it will shutt off about three times in a row then it goes on and onand on again for hours and hours. I was reading about the MAP SENSOR? Any ideas I will try them. Sorry to say it was nothing to do with the ignition although it was a good theory. Thanks for all your help.

The fluttering leads me to believe you ran out of fuel…if your fuel pump is intermittent this can happen. Caddys usually have a rather vocal fuel pump… Do this…turn your key all the way on/no starter motor…and listen…you should hear a low whining…or a hiss…thats your fuel pump. Turn it off and on several times to see if you can hear it. Sounds funny but if you actually KICK your fuel tank you can get a sticky fuel pump to start pumping…lol. The fuel pump relay is also a suspect I think.

If you have a garage that is nice and quiet that helps a lot. I am thinking that you may have an intermit fuel pump…or a dirty fuel pump relay. If you look in your fuse box (under the hood usually) try to find the fuel pump relay…once you found it…look at it and see if they use a similar relay for another subsystem…SWITCH the relays… see if your issue persists.

If you know how the relays work....they have a diagram on the side of them can actually use a wire to temporarily bypass the relay and wire the pump directly to power just as a test...  Thats getting a bit more technical for you I know, but these are the things I do within the first 20 minutes of troubleshooting....its ez if you know how the relay works....the relay is just a remote connects two leads together to power up a just bypass the relay switch and supply power directly to the other terminal thus bypassing the whole affair.....but if you see a similar relay in the can swap them no problem to try and troubleshoot this.  Now if the new relay does the same thing then you are having a wiring issue...usually a ground wire getting corroded or dirty....Just an idea.

I have the same problem with a 2000 Mercury Sable Wagon. Mechanic suggested that it was the idle air control valve…

OK so today it shut off again but I paid attention…it starts perfect then I take of in drive and it starts to rev up and down and then it shuts off…it did this four times in a row even after restarting and then it finally remained on. Any ideas?