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1999 Seville STS
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48 Posts
Discussion Starter · #1 ·
My 99 STS recently starting having a rough idle and sluggish acceleration. 130k miles, original plugs and wires. Any thoughts on what it could be? It has been this way for about a week and it's driving me crazy.
 

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'98 STS (RIP @ 206,xxx miles)
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4,854 Posts
....130k miles, original plugs and wires. Any thoughts on what it could be?
Welllll, there could be more than one cause but you have identified an excellent starting point.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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73,392 Posts
Yeah, that ^^^^ :holycrap: You're WAY overdue for plugs and wires; read the owner's manual....

Do a plug and wire change to AC Delco #41-950 Platinum plugs (same plugs as the original DENSO or AC Delco in the engine now) and a new AC Delco wire set before you start chasing other problems. Pay VERY close attention to the proper coil-to-plug wire sequence.

Pull the Diagnostic Codes from the car's built-in system and see what, if any, problems are identified.
 

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2006 Cadillac DTS Luxury III 135K
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453 Posts
possible timing issues or wrong firing order, clogged cat converter so many things could be wrong or it could be simple
 

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2006 STS V Tango int
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2,341 Posts
Yea a basic tune up sounds in need, especially a TB cleaning, plugs and wires and possibly a coolant flush
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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73,392 Posts
It could be mass air flow sensor
If he doesn't have either the SES light or a MAF code, then it isn't the MAF - in his car even an iffy MAF will throw one of a bunch of codes which point to air leaks and bad sensors - but he might want to check the electrical connector and also check the IAT near the air filter box.

"Timing"is controlled by 2 crank position sensors and a cam position sensor - any faults there and he gets stall codes and misfire codes as well as a flashing SES. Original plugs and wires ?? That should mean that no one has fooled with the plug wires, so they're probably OK on the proper coil towers.
 

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1993 Cadillac Eldorado Sport Coupe 4.6L Northstar "Y"
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130 Posts
Plugs for sure, highly doubt its the wiring. I would start at the plugs though and go from there, do you feel any "bucking" or "hesitation" while your accelerating? and if so, does it happen at a particular speed?
 

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2010 DTS
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88,120 Posts
Plugs for sure, highly doubt its the wiring. I would start at the plugs though and go from there, do you feel any "bucking" or "hesitation" while your accelerating? and if so, does it happen at a particular speed?
What makes you say that? If the wires are original, they're 11 years old.
 

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1993 Cadillac Eldorado Sport Coupe 4.6L Northstar "Y"
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130 Posts
Because mine are 17 years old and nothing wrong at 215k miles, I am just trying to pin point where it is obvious to start, because typically when you do a "routine" tune-up, its uncommon to need wire and boot replacements for the plugs.

*edit* depending on how the owner treats the vehicle of course, if this poster has good upkeep with the vehicle and especially at only shy above 130,xxx miles, i dont think this poster needs to be looking for wires/boots for his/her issue. Lets all remember that spark plugs are expected only to last 100,000 miles.... On top of that you may be right in a sense, i mean who knows? mabye she just needs to reseat the wires because of 1 or 2 being loose at the boot/plug. We will never really know until this poster tries these ideas and we know for sure. Any suggestions help in these cases! :D
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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73,392 Posts
Plugs for sure, highly doubt its the wiring. I would start at the plugs though and go from there, do you feel any "bucking" or "hesitation" while your accelerating? and if so, does it happen at a particular speed?
There have been many, many pre-2000 Northstars come through here with the OP's exact symptoms. In almost every case an inspection of the plug wires revealed either tracked plug boots or outer shield cracking with resulting arcing to ground. At 100 kmiles+ the plug wires have outlived their design life. Time for a complete plug/wire change.

You might want to go down to Discussions: Item Specific; Technical Tips and Discussions: Engines; Northstar Performance and do some extended homework.

BTW............. Welcome Aboard !!!!:highfive:
 

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1999 Seville STS
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48 Posts
Discussion Starter · #12 ·
You guys are right, I probably should have the plugs and wires replaces. I will not be able to do this myself. Before I go calling around for prices, how much should I expect a shop to charge me for this? I am assuming my Cadillac Dealership in town will be more expensive than anybody else.

I will try to pull codes this afternoon, its just been so freaking cold here in Iowa the last few days I haven't wanted to spend the extra few minutes in my car pulling codes haha
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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73,392 Posts
The book rate for spark plugs is just about 2 hours. The proper set of AC Delco plugs and wires will list at about $180, so if you're unable to do this yourself you're looking at $180 + 2 hours labor - easily $300+.

On your pre-2000 engine changing plugs and wires is not rocket science - a gearhead friend and a few common hand tools and you're good to go. Read up on the procedure down in Discussions: Technical Tips and Engines: Northstar Performance.

BUT you still need to post all your stored DTC's - there may be further hints there.
 

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Super Moderator
2010 DTS
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88,120 Posts
Because mine are 17 years old and nothing wrong at 215k miles, I am just trying to pin point where it is obvious to start, because typically when you do a "routine" tune-up, its uncommon to need wire and boot replacements for the plugs.
Somewhere back a few years ago there is a rather long detailed post by me entitled "Stutter, Engine or Trans?" if you care to search it out and read it. Short version is after the fuel rail recall was done to my '97 Deville I developed what turned out to be a misfire (I wasn't 100% sure, hence the title). Long story short, after replacing the plugs to no avail, I replaced the wires (at 75K) and that cured the problem. Like you, I did not expect them to be the problem. I now have a different view of ignition wires.
 

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1993 Cadillac Eldorado Sport Coupe 4.6L Northstar "Y"
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130 Posts
Well you learn something new everyday! :D
As generality's concern i was thinking it had to be the plugs, but i also stated "depends on how the owner is treating there car" (garage kept, drive ALOT, etc.) but this post is really making me start to look around later this weekend and inspect my wires to see any noticable cracking at the boots and see if any replacement is needed. Im installing a fresh battery ground and potentially a Voltage Regulator, so i mineaswell take care of some other things while im at it. Thank you for posting this information, this sorta helps me as well if i see anything wrong with them (havent experienced any misfires or bucking lately) but you never know. As far as the Poster is concerned, he/she should definitely get a full plugs/boots/wire exchange via garage visit or do-it-yourselfer.

Just make sure *POSTER* if your doing it yourself, you either want to use different colored permanent markers to mark both plug location and at the coil so wire installation is easier, or you can easily just take it easy and do one at a time! :thumbsup:

Hope these friendly Cadillac Drivers have given you the information you need, and apologize if i could not give full potential statements of the necessary issues.
 

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2010 DTS
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88,120 Posts
A word to the wise. Leave well enough alone if you are not having any problems. As I said, my misfire started after the fuel rail recall was done. In order to do that they had to pull the left bank plug wires and move them out of the way. Apparently moving the old wires around caused the problem. Visually, they where perfect. No external breaks or cracks at all, but it caused an internal problem that caused a misfire under a light load. It ran perfectly at WOT.
 

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'98 STS (RIP @ 206,xxx miles)
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4,854 Posts
....but this post is really making me start to look around later this weekend and inspect my wires to see any noticable cracking at the boots and see if any replacement is needed.
As far as the plug wires are concerned, the "easiest" inspection is a visual inspection with the beauty cover removed on a dark night. You might see a corona glow, but you would not want to see any arcing. It would help to have a "trusted" friend torque brake the engine in gear to simulate normal engine loads and greater demand on the plug wire insulation.

Plug wires slowly become less and less flexible over the course of several thousand thermal cycles and moving them around for "inspection" is counterproductive. Avoid moving the wires if possible !!
 

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1993 Cadillac Eldorado Sport Coupe 4.6L Northstar "Y"
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130 Posts
A word to the wise. Leave well enough alone if you are not having any problems. As I said, my misfire started after the fuel rail recall was done. In order to do that they had to pull the left bank plug wires and move them out of the way. Apparently moving the old wires around caused the problem. Visually, they where perfect. No external breaks or cracks at all, but it caused an internal problem that caused a misfire under a light load. It ran perfectly at WOT.
Well then! This makes me want to change them out for fun, just so i never have to deal with that. Thank you
 

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1993 Cadillac Eldorado Sport Coupe 4.6L Northstar "Y"
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130 Posts
Plug wires slowly become less and less flexible over the course of several thousand thermal cycles and moving them around for "inspection" is counterproductive. Avoid moving the wires if possible !!
Well i know this as far as being an electrician myself. As i say with anything else i touch under any hood i own, "Dont touch it unless you feel comfortable replacing it." :tisk:
 
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