Another Rough Idle Saga Base 2000 Deville
 

I have posted this over at *********, and I wasn't sure if the same users were over here, so I thought I would get ya'lls advice as well.

About the car: Base 2000 Deville, with 80k. Purchased from a family member, dealer maintained from new.

Rough Idle developed as well as a blinking SES upon WOT, that would go away after idling back and running at normal highway speeds.

1. Replaced Plenum, did not solve problem
2. Cleaned and inspected MAF, I later learned not to mess with it (what guys at ****** said)
3. Week later on 1.5hr drive constant SES with blinking upon WOT. Had codes pulled along the way (before I knew I can do it in the car!) Had Two of the same codes in the history, Misfire on cyl #3. Arrived at destination, let her rest and SES was gone
4. Spark plug and boot replacement, did not solve problem
5. Self Dx revealed PCM Codes P0300, P1189, P1617 History, oil was low a couple of days ago, hence the oil codes and has been topped off, accidentally cleared the codes
6. Ran the car per GM driving instructions at Cadillac Dx Page, yielded no codes
7. With a little WOT, blinking SES comes back, if I run the PCM dx while it is blinking, I get P0300 Current, when it stops, I get No Codes
8. Cleaned TB and still have the same response as #7 above

Still rough idle, still confused, still can't find the right answers.
Any ideas are greatly appreciated,
-C

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RE: Another Rough Idle Saga
 

I suggest coil pack. Just wondering why you replaced plenum?

RE: Another Rough Idle Saga
 

me too .. why was the plenum replaced ?

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Katz,

Can he swap the coil component for #3 and see if the mis-fire from #3 moves with it?

RE: Another Rough Idle Saga
 

I guess you could say the reason why it was replaced was ignorance. Also, from reading around, it appeared that the plenum is a common issue in the rough idle arena, not to mention it was only 20 bucks, I'll try 20, before 250 any day.

FYI:
Re-cleaned the TB (got in there with a toothbrush this time) and tightened all of the hose clamps assc. with the air intake to plenum and so far I would say the rough idle is about 90% better. However, I am worried that this is like a bad case of hiccups.... just when you thought they were gone....

However, I am still getting a blinking SES on WOT. I also feel like there is a vacuum leak in the passenger side of the intake manifold closest to the windshield. I can't quite get a fix on it. I am going to pull the manifold again, replace the manifold gaskets and clean the blow-off valve in the manifold. (all ideas from the other site)
I know I am dragging my feet on this coil issue, I just hate to waste the $$$.

RE: Another Rough Idle Saga
 

2000 has one coil for each bank and they don't interchange, no wires, this is coil overplugs.

I have to say that the plenum trick is a new one on me. Vac*** leaks can make the car run bad but generally poor idles come down to spark and fuel. Messing with a second hand plastic part just does not seem like a good call, even if it was only $20. Just my opinion.

On the coil issue just wondering why you think you'd be wasting money? You're driving a 9 year old car for goodness sake, these things break down over time. A set of AC Delco wires for cars with plugs & wires is $240, each of the 4 coils is $90. I don't think a coil pack for your 2000 will cost close to that. Maybe you need to replace your plugs too can't see where you mentioned if you've done that. To be honest that is what I would have done First.

SES light: Severe Misfire Detected
 

it never hurts to have a really clean intake. Seafoam continues to be a stock item in my shelf of cans and bottles. i get the liquid pint and load it into a spray bottle, more for your $$$. I also use a long wooden stick to scrape.

ditto on the replace the coil,
if it isnt that (probably WILL be) you got a spare that you WILL need at some point.
SES light: Severe Misfire Detected

plenum .. have you maybe created a vacuum issue with seals now leaking? vacuum leaks will give you rough idle but no way a mis-fire.

the misfire goes to the specific components of the cylinder with the misfire: coil, plug, coil to plug connector, fuel injector - period.

RE: SES light: Severe Misfire Detected
 

Great minds think alike Stealth!

Cadillac Problems
 

If your car is running rough check your EGR Valve Ok it may be stuck in open position or it needs to be replace should fix the rough idle situation. they build up carbon I had the same problems with mine and the EGR Valve was the problem and I changed the Map Sensor, EGR Valve seems to be your problem.

Let me know what happens ok!
Good Luck,