2000 Bonneville has been running jerky under acceleration. The SES has been on for some time. The Bonneville sat for 2 weeks, and when I took it on the highway its power became week, and when it was at full acceleration above 40 mpg, the SES would flash until I let off the pedal, and then would remain on solid.

Went to AutoZone and they pulled three codes:

P0442
P0305
(LOST THE THIRD ONE).

The codes showed a missfire in cylinder 5 and 2 vacuum leaks.

I bought new plugs, replacement PCV valve, new gas cap and MAF cleaner. In the AutoZone lot I changed the PCV valve, cleaned the MAF sensor and replaced the gas cap. Also pressed down on the plug wires. Took it on the highway home and it ran much better, and no flashing SES under full throttle.

At home I went to replace the spark plugs. Did the research on this board and debated if I wanted to change the plugs because of the back 3 plugs. Did the front 3 and found the plugs very easy to change, but near impossible to get off the plug wires. After the front 3 were completed, went to the rear three plugs. The first two came out much better than expected. No problem at all except getting off the wires. I didn't pull the rear engine lift bracket- no need to I thought (also it is 13 mm on my Bonny, not 10mm as on others). Went to pull the last plug wire (#6) and could not get it off. 30 minutes to change the first 5 plugs, and 1 hour trying to get plug wire 6 off. I the pulled the engine lift bracket and tried again. No luck. Another 30 minutes of trying and.... I broke off the plug wire. This sucked because I didn't buy wires and was planning on changing the wires in a few months. Spent another 30 minutes trying to get the plug electrical socket off, and it finally came off. Put the socket wrench on the plug and it wouldn't fit. Seemed the metal contact inside the plug socket had welded itself to the plug. Another 5 minutes getting that piece off and then pulled the plug. Off to Napa for wires.

Upon return I replaced the wires, starting with the back first. No major issues, although the old wires had labels 1-6, new belden wires were not labeled... no bg deal but it was nice to have the wires labeled. Number 6 installed, no problem. Next, number 2. When I got to the coil side I discovered corrosion on the metal male reciever. Suprised, i slightly sanded it and sprayed MAF cleaner on it and went about my business. Went to plug 4, replaced it and no issue.

Now to the front. Started with plug 5 and when I pulled the old wire off the coil side I noticed the same problem as seen on cylinder 2, but only worse. Sanded it again, little MAF cleaner sprayed on the terminal and then replaced the final two wires.

No corrosion was found under the other 4 terminals, just the 2/5 terminal, which is very surprising because they are in the middle. I WAS THANKFUL I BROKE WIRE 6 OR I WOULD NOT HAVE FOUND THE CORROSION under 5/2 for months. The plugs all looked fine, so I am confident that the corrosion caused the misfire. A super simple fix- yet I never saw it or even imagined it.

A few notes from the repair:

Cleaning the MAF and changing the PCV took seconds, as easy as it gets thanks to Dan Thurs pictured writeup(*). That along with the gas cap change made the car run many times better.

The plug wires, not the plugs were the challenge in replacing the plugs. I used a huge old comforter to lay on the engine to protect the engine and myself on plug 6. On the new plug wires I put a touch of dielectric grease in the sockets.

NGK plugs were the old plugs. Not sure how they got there, we bought the car with 40k miles. Maybe my wife had them changed while I was deployed? Hadn't seen NGK since the my minibike days of the 1970'*.

Bottom line- best $160 in parts I ever spent on the Bonneville. It is running better than ever with the new plugs, wires, pcv valve, gas cap and cleaned MAF. Can't imaging what a dealer would of charged and how long it would have taken to find the problem. The parts were so cheap in the big scheme of things it was cheaper to do all of it and then see what was wrong. In this case, standard maintenance was the fix.

Take a can of carb cleaner an dspray all the vacuum lines, EGR tube, and around teh injectors while the engine is running. If the RPM changes you have a vacuum leak.