: 03 STS rough IDLE P0300 & U1016 Code

08-24-06, 06:51 AM
Hey guys, I need some help. I've got an 03 Seville STS with 70k miles on it and it just started idling rough when warm with the A/C on. With A/C off, it still idles a little rough, but not as bad. Also, it seems to sputter a bit when under WOT and if at WOT for more than 5 seconds, the Service Engine Soon light flickers and sometimes stays on. When I dump the codes, I get a History P0300 and occasionally I see a History U1016.
I've looked up the P0300 (multi-cylinder misfire) and the U1016 (lost communication with PCM).
I'm a little low on $$ right now due to family problems so I'd appreciate some advice on the least expensive way to approach the repairs.
Any help would be appreciated.

08-24-06, 07:53 AM
Could be wires, plugs or a coil. I think it's highly likely a wire/s. If you have an ohm meter you can check the resistance of each wire (i can post back the ohm range for you later). You can also do the same for the coil/s.

08-24-06, 08:58 AM
The 03 northstar is coil on plug... There are no sparkplug wires

Clean the throttle body, and then clean the EGR Valve...
Other then the idle... does it run OK... if so try replacing the Air bypass valve but on an 03 this shouldn't have failed... 00,01,02 and some early 03s have an issue with crank sensors which will cause a stall but generally not a lousy idle..

08-24-06, 10:37 AM
:bigroll: OK, apparently I know nothing about 98+ n*....

08-24-06, 12:27 PM
UR7x, can you point me to a howto for cleaning the throttle body and EGR?
Also, any idea what caused the U1016 code? Could it have been when I cleared the codes?

08-24-06, 12:30 PM
Oh, and yes it does seem to run OK above idle (Except for WOT), although there is a slight stumble when first accelerating off idle.

08-24-06, 04:40 PM
Cleaning the Throttle body is easy... use an old toothbrush... or your finger and a can of Throttle body cleaner (what else) its basically squirt, scrub, wipe... clean the front and the back of the throttle blades...

However the fact that is is stumbling at idle and WOT sound like it could be the EGR valve... It is supposed to be closed in both of those conditions... buy an EGR valve gasket at the dealership and remove the EGR valve and check it for deposits.

The "U" codes are normal and will appear from time to time... Ignore it...

How many miles on the car? It could be a bad spark plug too...

Or a vacuum leak... There is a vacuum line under the engine trim cover at the back that tends to rub at the elbow and can cause a vacuum leak but vacuum leaks are usually only apparent at idle.

08-30-06, 06:41 AM
Well, it turned out to be the #3 coil so it took a coil pack (not covered by my Continental Gold warranty! Thanks guys!) and the #3 plug. Also cleaned the throttle body and the injectors.
BTW, had a broken front motor mount which Continental Warranty also DID NOT COVER! GRRRRR!
Anyway, thanks for the help guys!

08-30-06, 02:42 PM
Sounds like a great warranty. Hope you didn't pay too much for it.