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'05 Deville DHS
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Discussion Starter #1
2005 DHS. 110K miles on the clock. Still has a nasty idle sometimes. Very rough. Latest trick is bucking at 55 MPH on the highway. 1600 RPM, not warmed up yet, and it seems to be spitting once in a while. Sounded like 2 pops through the intake the other day when leaving a parking lot (hot). No codes other than stupid seat heaters and such. No engine/trans codes.

Cleaned throttle body a few weeks ago. Also checked for vac leaks with a can of starting fluid. No leaks found.

Also ran a tankfull of Techron after cleaning t-body out.

Just came back from a 300 mile round trip of 80MPH. Runs out fine, MPG could be better I feel.

Fuel pressure was checked and good. FPR is not leaking. Coolant level hasn't budged since purchased last month and about 4K miles.

Now what? Ideas?
 

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'05 Deville DHS
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14 Posts
Discussion Starter #3
Currently running some Autolite trash. Will pick up some 41-987s. Still have them in my basket to check out online. How often do the coil packs on the 2004+ go bad and is there a way to bench test them? The bad idle is intermittent so not 100% sold on the plugs themselves yet.

Thanks!
 

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'05 Deville DHS
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14 Posts
Discussion Starter #4
Alrighty. Replaced all 8 old AutoLite plugs with the proper AC Delcos. Seems to idle a tad better now. Will know for sure on my 800 mile road trip in 8 hours. I do NOT want to replace the rear plugs in the near future AGAIN. Lost a spark plug socket in the front bumper somewhere.. Both nuts on the EGR tube had to be replaced due to loss.. Sheesh.

Hope it's all better now.
 

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96 Concours, 05 DHS
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184 Posts
How often do the coil packs on the 2004+ go bad and is there a way to bench test them?
My 05 DHS carbon-tracked a plug at 110K, so I replaced the rear coil cassette and plugs. The front cassette had already been replaced by the previous owner sometime before 105K (when I bought it). So maybe 100K is a typical lifetime.
 

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98 eldo/KD54 w/N37,T96,QA1,D55,DS3,U1Z. U3R next
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2,125 Posts
My friend has just acquired a deville, an 04 model.

The coils pictured must be the "improved" vertical coil connector design because his vehicle has horizontal cop set up with some horribly designed connectors that plug into the coil..

He acquired the vehicle from a young man that was in way over his head in understanding how this thing runs. After discovering 3 bad coils and realizing that the connectors were all heated rotted that plugged into the coils we tried to purchase new connectors. Yet, they were the newer design picture above and weren't compatible with his original coils.

So, I suggest if you still have the horizontal mounted connectors that you check all of them for fit into the coils because they can back out of the coil as we unfortunately discovered. I assume that's why they were replaced by the newer improved design.

Horizontal mounted design BWD E402
 
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