98 DeVille cranks ok and fires but shuts down immediately
 

Hello,

I am the family Saturday mechanic and my sister in-law's 1998 De Ville with the Northstar engine and approx. 160K miles has just decided to go ahead and start but not stay running. I have not been able to look at the car in person yet to see if there are any codes or messages on the dash display. My first question to her concerned whether a security light or symbol was showing up on the dash. She says there are no messages and the only indicators that remain on are the seatbelt and oil pressure. The engine cranks normally and it does start but shuts down right away over and over. I intend to use the diagnostic function with the dash display in case anything is indicated there when I get the chance.

It almost acts like a fuel problem, as though the injectors are being turned off right after starting. Don't think there is a lack of fuel or a fuel pump problem. The car was working fine the day before. I don't know where to even start looking.

I'm aware of the security and anti-theft systems in these cars related to the chips or resistors in the ignition keys. She was going to try the other key but it's my understanding that the engine won't even crank and a security warning will show up if this is the problem.

I should point out the two months ago, after a heavy rain, she buried the nose of this car in a deep pool of water and flooded the engine. It appeared the air intake got below the water line and sucked in enough to kill the engine. I got all the water out of the cylinders, intake manifold and ducting, changed oil and spark plugs, replaced the air filter and it started. It has been running fine ever since. Even spent a week in an airport parking lot and fired right up. Probably has had at least 1000 miles put on it since without incident. From what I could see, nothing electrical got wet in the engine compartment. I checked all the grounds and main wiring connections to the fuse/relay panel and they were all clean and dry.

This car is stuck in her driveway now. I'm not going to be able to do too much there. Have the feeling it must be something fairly simple but not sure where to start looking. Appreciate any advice. Thanks.

Most likely, it is a dirty/defective Idle Speed Controller. It happened on both my 1989 Sedan Deville and my current 2002 Deville. Clean it off, clean the plates, drive it for a while to burn off any excess cleaner, and it should do it. If it doesn't fix it, it's probably more, but this is a simple fix.

TS

Thanks for the tip
 

Thanks to SimpsonTruckDriver for the tip about the idle speed controller. This makes sense considering all the water that this engine swallowed a couple months ago. Certainly some of the water had to get into passages in the throttle body and may very well have affected the function of this part. To date, I have not had a chance to look at the car and check anything out. She said it now starts and runs but hasn't driven it much. The ISC will be the first thing to check and clean when I can or when she can get it to my shop. Appreciate the lead. Thanks. Ruckle