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1990 Sedan DeVille, 2003 DeVille
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16 Posts
Discussion Starter #1
2003 Deville... I have had an issue where when sitting idle in drive the engine will jitter and return to normal. I will feel the same jitter when coasting and accelerating sometimes and that can be a bit heavier than when sitting idle. If the A/C is running it is more noticeable. When driving it runs fine but the acceleration will sometimes increase even if I am holding the accelerator steady. I have NO CODES. I get terrible gas mileage (around 10 to 11mpg average). I am thinking either I have a bad injector(s), bad spark or maybe a weak fuel pump? I am kind of stuck as to what I can look at next or consider to be an issue. Anyone have any thoughts?
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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69,886 Posts
Take the car out of the city and perform several spirited runs to 70+ and then forced coastdowns with the stick in 1. The transmission will NOT let you break anything.

Google "cadillac forums northstar wot procedure".

10 or 11 city/slow traffic mpg is normal, especially with A/C on - that alone takes 6 - 9 hp to run.

Study this - all of it. Written by a CF member who was a GM Cadillac Northstar System powertrain engineer. Especially the article "Occasional full throttle operation is good ..."

 

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White Diamond '03 DHS (with DTS floor shift)
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87,194 Posts
Might check for a leaky FPR.
A good TB cleaning may or may not help, but sure can't hurt and is probably way overdue.
 

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Registered
1990 Sedan DeVille, 2003 DeVille
Joined
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16 Posts
Discussion Starter #4
Take the car out of the city and perform several spirited runs to 70+ and then forced coastdowns with the stick in 1. The transmission will NOT let you break anything.

Google "cadillac forums northstar wot procedure".

10 or 11 city/slow traffic mpg is normal, especially with A/C on - that alone takes 6 - 9 hp to run.

Study this - all of it. Written by a CF member who was a GM Cadillac Northstar System powertrain engineer. Especially the article "Occasional full throttle operation is good ..."

Thank you. That information is helpful.
 

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Registered
1990 Sedan DeVille, 2003 DeVille
Joined
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16 Posts
Discussion Starter #5
Might check for a leaky FPR.
A good TB cleaning may or may not help, but sure can't hurt and is probably way overdue.
I cleaned the throttle body as best I could. It is constantly over 110 degrees outside and recently humid. I didn't take it completely off. I had not considered the Fuel Pressure Regulator. Thank you.
 

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2005 Base CTS work at Pullen solenoids Glass Factory for 36 and a half years
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268 Posts
If you can get it scanned that would be helpful and it should also show you what your fuel pressure is.

Roy
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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69,886 Posts
No reason to remove the TB. Block the throttle wide open and, using an old toothbtush and lint free rags, clean in as far (both sides of the butterfly) as you can and don't get excess spray into the plenum and intake manifold. Make VERY sure the rubber intake ducting is correctly replaced with NO air leaks.

His 2003 FWD Northstar does not monitor fuel pressure or oil pressure. That info comes from rented test gauges.

His car also has its own built-in DTC scanner/memory/system. Use the correct model/year section of the sticky thread "How to pull codes". These are the DIC control buttons you use to enter the OBD-II system. There is an embedded link to all his OBD-II DTCs.

DIC controls.jpg
 
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