Smithw500 here. Hello to everyone!

[Smithw500]

Hi everyone. Smithw500 the new guy here.
Bought a 97 Bonneville SE about a year ago and love it. Just last week found a 2000 Bonneville SSEI with 44,000 original miles on it so I had to buy it. Found that it has all the typical problems from what I've read so far. Saggy headliner (new one ordered already), all passenger windows and locks inop (fixed now thanks to the article I read on here about the splice under the driver's seat), and a leaky sunroof (partially fixed again thanks to articles I've read on here).
Now have a problem I thought I could pick everyone's brain. Had a surge/miss with load on engine. Typically going up hills before it downshifts. Been a mechanic my whole life and figured it was ignition related. Bought 3 OE coil packs, OE ignition module, AC delco plugs that were recamended in the owners manual for this car and Napa premium wire set. Now the surge/miss has gone away under load but have a miss at idle in P/N. I am thinking it's the Napa wires since everything else is new OE. No vacuum leaks. I'll probably just buy the AC delco wire set but didn't know if there was a common cause that I was unaware of with this engine.
Thanks for any suggestions.

[sseilmnop]

Do you have a scanner? Good scanners will give you a misfire table by cylinder. Even if your getting P0300 random misfire its likely only one cylinder. The cylinder closest to the vacuum leak.

I have found that most misfires at idle are vacuum related!! (injector o-rings, vacuum fitting, boost bypass, egr tube, vacuum fitting on top of supercharger, TEE UNDER THE SUPERCHARGER SNOUT)

Most misfires under power or boost are spark related. (plugs, wires, coils, etc..)

So you now only have misfires at idle, so its vacuum. Have you replaced all the rubber ends on the vacuum lines? If you still have the stock ones there not great. If they weren't leaking they are as soon as you pull them off. Pinch them and you will see little cracks. There is also an EGR tube from EGR valve to intake manifold that can crack which is an instant leak. I never had much luck with spraying carb cleaner, I recently smoke checked my car and found the the Vacuum fitting on top of the supercharger was leaking.

I've had 7 SSEi's so over 10 years so far!

44,000 miles!!!!! Does it still have the stock black plastic lower intake gaskets? Change them and the plastic coolant elbows as soon as possible and you got a great dependable car!!!! Use aluminum elbows from dorman and aluminum LIM gaskets!

[00Beast]

I agree to double check for vacuum leaks. All the tee's in the vacuum harness around the engine get pretty crunchy, and like to break, especially after sitting for 17 years (44k miles means it's done a lot of sitting). I'd pull the lines off and inspect each component. They might fall apart as you take them apart too.

[Smithw500]

Thanks guys! I ohmed out the new Napa wires I got and one had way more resistance than the others. I got a set of AC delco wires and the dead miss went away. Still does idle a little rough. I already bought a bunch of vacuum Ts and line, so I'll replace em all and see what happens. I'll also get a set of those intake gaskets and replace the coolant elbows while I'm at it.
Thanks for the help guys, I appreciate it.