Buick - Parkavenue :: 1995 - Occasional Miss When Cruising Along At Highway Speeds And Slightly Rough Idle

Got a strange one here. 1995 Buick Park Avenue, supercharged 3800, 159K miles... an older car, but an unmolested one. A little over a week ago I began to notice an occasional miss when cruising along at highway speeds, along with a slightly rougher idle. Both the fuel filter and the plugs/wires predated my ownership of the car (a little more than 6 months); so seeing no obvious culprit, I replaced them and hoped for improvement.

Unfortunately, neither had any impact. The missing continued to become more noticeable. It was never present under acceleration. Most of it was like a split-second long version of "bucking" that could be observed while cruising at lower (<2000) RPMs. It was also very noticeable at idle. Eventually a code was set: P0341, camshaft sensor issue. If the story had ended there, it would have been just another night in the garage. But it didn't.

As I was noticing the aforementioned symptom increase, I also noticed my voltmeter would occasionally "twitch" in the downward direction. Eventually I had an incident where I came to a stoplight... transmission in Drive, foot on brake, gauge dropped to around 10-11v. It returned to 14v momentarily, but dropped back down, held there for several seconds, returned, etc. No particular rhyme or rhythm. Of course my first guess was that the alternator was failing; a separate problem from the other.

I checked all the relevant connections (at the battery, at the alternator, etc), and cleaned them for good measure. All were tight, relatively clean, and the cables showed no resistance on the ohmmeter. It happened that I had another correct alternator on hand (used/working pull), so I swapped it in. No change. I reinstalled the original and was back where I started.

On my most recent drive, I noticed both issues had become very noticeable. The drop in voltage was happening at nearly every stop, and the missing was happening a few times per minute while coasting along. There seemed to be some correlation between the missing and voltage fluctuating, but it wasn't absolute.

I decided to attack the voltage issue again. Re-checked all the cables; same result as before (all OK). Looked all over the car for possible bad grounds, loose connections, or other visible problems, but found none. My next thought was to run a jumper from B+ to the voltage regulator's Sense input (have seen issues there on more than a few older vehicles) - but after reading that this car uses the PCM as the voltage regulator, I didn't proceed.

Just to be certain I'm going to have the alternator tested by the local auto parts store. But I suspect it'll pass.