My Rough Idle Story, So Far...

[SuperC]

So I bought my 2000 base deville a couple of months ago and of course, right after I bought it, she developed the infamous rough idle.

After finding, and reading this forum, I decided to replace the plenum. Which, by the way, was a little intense for me. The first and last time I worked on an engine was shop class in high school 10 years ago. Nevertheless, I got that done and starter fluid detection yielded no leaks post installation.

Retrospectively, perhaps I was a little too hasty on the plenum replacement, I had a SES light blink while playing with someone in a mustang on 75. It went away and came back for a few hours and is now gone again. I did, however, have the codes pulled and I have a misfire on cylinder 3.

I am currently out of town and away from the everything I need to do a spark plug replacement. So, it looks like its gonna run me $300ish to have them changed. Which doesn't make me too mad, especially considering that you guys have said it is a PITA.

So, am I headed in the right direction here? Is there anything else I can do BEFORE I have this done? If this does not solve the problem, how can I trouble shoot other possibilities causing the rough idle, is there a way two determine whether or not the coil pack is functioning correctly?

By the way... 2000 Base, with 80K. The car was owned by an old lady, which she serviced regularly. However, I called the dealership and they said it was difficult to see what service has been done. Are they feeding me BS?
-C

[Ranger]

I called the dealership and they said it was difficult to see what service has been done. Are they feeding me BS?

Any service performed by a GM deal will be available to them. Any service performed by anyone else will not.

[WoodShoe]

youre paying someone 2 change your spark plugs? its not that much of a pain. you can do it in 30 min. Take off the coilpack if youre really annoyed with the clearance back there. other than that there is no problems. and i seriously doubt your coils have gone bad. i bet its the wires.

[SuperC]

Originally Posted by Ranger

Any service performed by a GM deal will be available to them. Any service performed by anyone else will not.

All work was done a the dealership, the car came from a family member. I guess the guy at the dealership was just being lazy... I'll call'em back and give'em hell this time, thanks for the input.
-C

[SuperC]

Originally Posted by WoodShoe

youre paying someone 2 change your spark plugs? its not that much of a pain. you can do it in 30 min. Take off the coilpack if youre really annoyed with the clearance back there. other than that there is no problems. and i seriously doubt your coils have gone bad. i bet its the wires.

Pain or not, I am in Jacksonville for two weeks (home base is gainesville) so unfortunately, I am gonna have to suck it up not to mention the rough idle has nearly driven me to drink.

That being said, since there are no spark plug wires, what exactly am I looking for in terms of "wires"? When I replaced the plenum, I pulled the fuel rails and also unplugged 8 wires. I am assuming this is what you are referring to. If so, out side of frayed wires, how can I determine if the wires are bad?

Forgive me for being ignorant, I am at the very beginning of a long learning process.

Thanks for your help!
-C

[Crown Vic Owner]

Stupid idea, DONT do this unless someone else OKs it, but could a piece of carbon nailed a plug?


WOT cleanup?

[submariner409]

WoodShoe doesn't realize that 2000+ Northstars have coil-on-plug ignition and do not use plug wires...the wires you unsnapped are individual injector trigger wires from the PCM. The 8 ignition coils are triggered by wiring to each coil cassette ICM in one end.

If you need to get the dealer in JAX to change the plugs, go for it.......it can be a bear without a hoist and tools.

Make sure that your air intake ducting from the filter box to the throttlebody is correctly oriented and the clamps are tight. An air leak between the MAF and throttlebody can show up as a low-speed miss or stumble.

[SuperC]

Alright... Bad news...
Spark plugs and what they referred to as "boots/wires" were replaced. She feels better, no hesitation on WOT, but there is still definitely still a rough idle. I am going to run it tonight with a little more WOT on the highway and double check my connections around the MAF.

Recap of what has been done:
1. New plenum/boot
2. New spark plugs/boots
3. Cleaned MAF with spray MAF cleaner

So correct my thinking on (if need be) on the next steps:
1. There was a misfire on #3, I am going to have autozone clear the codes just to make sure something else does not pop up.
2. Replace the fuel filter
3. Replace Rear coil pack (seeing that it is a misfire on three)

Do you guys think this is the correct order, or should I go straight for the coils?

Does anyone know what the part number is for the rear coil pack? is it ACD589 or ACD590 from Race Pages

Thanks,
-C

[submariner409]

There was no need to clean the MAF. Leave it alone. Do some snooping around in Northstar Perf. and read up on throttlebody (TB) cleaning. An hour job, toothbrush, rags, Throttlebody cleaner, (NOT carb cleaner !!). DO NOT shoot cleaner into a wide open TB. Block the gas pedal fully to the floor and stuff a lint free rag past the butterfly to absorb excess cleaner which would otherwise pool in the manifold and possibly hydrolock a cylinder. Cheap insurance. Scrub away, dry it all, and pull the rag with a hook or long needlenose. Check every one of the plastic/rubber vacuum and supply lines to/from the TB and PCV connectors.

read the stickys at the top of these forums...you can pull, read, clear, store codes right in the driver's seat in the driveway......no need for scanners or shops.......it's all built in.

[SuperC]

Thanks SubM!

I Used the diagnostic, however I accidentally cleared all the codes before I had a chance to write them down.

What I did get was PCM codes
P0300 History
P1189 History
P1617 History

As you know, misfire and oil level sensors, the oil was low a day or two ago and I topped it off.

I am going to run the car to the specs on the GM driving cycle sometime tonight. I will also clean the TB, following your guidelines in the morning and I will post the outcome(s) tomorrow.

-C

[tateos]

What about crankshaft position sensors? They are a known problem on these 2000s.

Also, what about a bad fuel injector - that would cause a misfire.

[Ranger]

Forget the fuel filter. If it where dirty enough to cause a misfire at idle, it would fall flat on it's face when you attempted WOT.

[SuperC]

Some other things I forgot to mention which may/may not help you guys, help me, that is.

Prior to plenum replacement, had blinking SES after WOT, which would go away shortly thereafter. I am assuming that was the misfire in the history.

After plenum replacement and a little WOT, had a blinking SES and then steady SES until I got to Jax (about a 1.5hr drive). After she rested, SES went away. I have also noticed that the rough idle is worse when the A/C is on.

No SES since plug change today, but I have not had a chance to really run her yet.


As for the rest if the ideas, thanks! Keep'em comming
-C

[Ranger]

A blinking SES light means "Severe Misfire Detected".

[SuperC]

After I got done studying, I took her out and ran her, per GM driving instructions from the Cadillac Dx Page.

1/2. Cold Start w/ AC and rear defrost = Rough idle which held pretty steady at about 800RPM
3/4. Acceleration 1/2 throttle and hold at 55mph = nothing to report, maybe some intermittent hesitation while accelerating.... maybe... too hard to tell
5. Deceleration = normal
6/7. Acceleration 3/4 throttle and hold at 55mph = about the same as part 3/4
8. Deceleration = normal

After which I gave it a GOOD WOT about 10-70mph, and noticed some fluctuant hesitation on acceleration and got the blinking SES (again) that went away after about 30s of 55mph. Got home and pulled codes and only got, IPM B0429 Current, which has absolutely NOTHING to do with my problem.

In the AM I will clean the TB, clear the codes again, and run it again and report back.

-C