7I have a '98 Bonneville SE with 172,000 miles on it. I bought it in April 2007 and it had 156,000 on it. This is what is wrong with the car.

I've been having a real hard time starting the car. Once I get it running it will keep running, but the longer it runs, the worse it runs.

I could not get the car to restart after work one day this past December. When I turned the key over I couldn't hear the fuel pump running. I depressed the schrader valve to see if I had any fuel pressure and I didn't so I checked the fuel pump fuse and relay and they were fine. I replaced the fuel pump and fuel filter.

The car will now start after several attempts and stay running, but it seems like its misfiring a little bit. I took it to Advanced Auto today but first thing today but for some reason the check engine light was not on. Its almost always on but when I got up there today it wasn't so I didn't have any trouble codes. I kept it running for a couple hours and the longer I kept it running, the worse it ran. It seemed to spit and sputter, the hotter it got and the more it ran the more it refused to accelerate. Above 3000 RPM'* there'* nothing. Today I checked the spark plugs and they all showed normal wear and were all still at about .060.

I also took it to a muffler shop today due to the lack of acceleration and had them look at the catelytic converter and it was at 684F. I had them put a straight pipe in and it did have a little more power but it didn't solve the problem.

This is what I've done to it since I bought it:
April 2007 - Replaced radiator due to leaks
Replaced valve cover gaskets due to leaks
August 2007 - Replaced plugs and wires gapped to .060. Replaced the oil pan gasket due to leaks.
February 2008 - Intake manifold exploded into pieces. There was a manufacturers recall on the fuel pressure regulator in 2004 that the previous owners never got fixed. The manufacturer'* recall put out that this could cause an intake manifold to explode so I replaced it myself then had the dealership replace the fuel pressure regulator.
Fall of 2008 - Experienced charging problems, replaced alternator, the 5 year old battery, starter/solenoid(the shop said oil leaks from the past destroyed them), then finally I replaced the battery cable. Charging system is fine now.
Fall of 2008 - Also around this time the car started making a horrible screaching noise on startup. When I revved it up around 1200 the noise would go away. Over the past year or so, this noise has steadily gotten worse to where I have to rev it all the way up to 3000 for the noise to go away. And when it does go away there is this rattling noise thats loud at first then steadily goes away over the course of 2 or 3 seconds.
December 2009 - I start it up on a very rainy morning and it shuts off a seconds later. After a couple attempts I finally get it to restart. I drive it to work, it ran a little and the voltmeter went down a few times while I was stopped at stoplights.

I suspect that it might be either the crankshaft or camshaft sensor, but I'm tired of spending money and time on the car without fixing the problem. It seems like every problem I have with it I have to go around my elbow to get to my rear end. Any suggestions would be greatly appreciated.

Are you getting an SES light? If so, go to a local Auto Parts store and get a free read to see what the DTC is. This will help narrow it down.

The squealing sounds like it might be an idler pulley going bad.

The voltage drop at a stop light is probably because of a low idle condition and not an electrical problem.

SES light? Is that a check engine light? If so, like I said before it usually is on, but for some reason was not on when I went to Advanced Auto to get it scanned therefore no trouble codes. I forgot to mention in my original post, on my way home when it was running at its worst, the check engine light was flashing.

If only it were flashing or even on when I was at Advanced Auto. I'd like to just bring it back up there but with the engine struggling as bad as it was I'd hate to cause more damage, or for it not to start and have to get it towed yet again.