View Full Version : '98 DeVille Northstar dies while coasting.

01-23-11, 10:31 AM
125k miles. When I'm coasting down the road 25-35 MPH only. My engine speed is 900 RPMs, but occasionally, it slips down to as low as 200 and sometimes dies. I put premium in it. Idle speed is 650 RPMs. I replaced the brake booster. What could be the problem with this?

01-23-11, 10:44 AM
What codes do you have?

01-23-11, 11:36 AM
:welcome: HI !! Welcome Aboard !!!

Follow N*Caddy's advice and read, study and practice the sticky thread ^^^ "How to pull codes".

When you're comfortable with using your car's built-in Diagnostic Trouble Code scan system, write down all codes found, nothing whether the suffix for each is Current or History. Return to the sticky and open the link with "obd2" in the URL. This will take you to a Master Index of all P,B,C, and U codes. Click on each code type for lists of their definitions. Write it all down and come back to this thread and post your findings.

N*'s reference to "CKP" is the acronym (another sticky ^^^) for CranKshaft Position sensor(s), those ignition/injector triggers which send timing signals to the PCM. One or both sometimes develop problems with a subsequent loss of timing output and the engine will stall and/or default into a fixed ignition timing of 10 degrees BTDC. If one or both is faulty whey will set a ^^^ DTC.

01-23-11, 02:42 PM
409 That ain't the Piper is it?

Anyways back to business. Here are all the codes that came up and their translations.

P0603 - Control Module Long Term Memory Reset
P1527 - Transmission Range to Pressure Switch Correlation
P1599 - Engine Stall or Near Stall Detected
B1552 - Keep Alive Memory (KAM) Error
B1558 - BCM EPROM Checksum Error
C1255 - EBCM Internal Malfunction

01-23-11, 06:55 PM
Well based on the codes I would say you may have a battery issue (check your battery terminals) but this is not related with the engine stall.
I believe the engine stall is caused by a vacuum leak, or an issue with the idle control hardware near the throttle body. Also check your overpressure valve (is known to be leaking).

01-23-11, 09:43 PM
I did have some terminal issues recently. That's fixed. I replaced the brake booster because I thought it might be a vacuum leak. Where else could that vacuum leak be? Is there any other ways to conduct a more specific test to narrow it down?

01-24-11, 10:40 AM
USS PIPER (SS 409) - '59-'62, then fast attacks and SSBN's 'till '82.

02-17-11, 02:26 PM
I'm still having this issue. I checked for a vacuum leak. Nothing there. What does seem to be helping it is putting in Fuel Injector cleaner, the RPMs still dip but usually not enough that the engine dies. Someone told me this may be due to the starter or cam sensors there. (he had a similar issue on his 96 deville) The car does have trouble starting when the engine is cold. I have to press the accelerator to get it to start on occasion. Has anyone else had this problem or know what I should check next?

02-17-11, 04:02 PM
There is no starter sensor. If the car starts only while holding your foot partially on the pedal, then I'd give the TB a good cleaning. You might have a carboned up IAC valve inlet.

02-25-11, 01:20 PM
Idle Air Control valve would be my first suggestion too. Pop it out and clean it and the passages in the T-body. Probably a lot of grime and carbon in there as mentioned.

03-01-11, 09:16 AM
The Idle Air Control valve can be faulty without setting codes. I would also take a look at any freeze frame DTC's you might have.