2000 PAU runs rough and hard start

Hi all,
I recently bought a 2000 Park Avenue Ultra with 130k miles on it. I bought it knowing that it had LIM problems due to the antifreeze being mixed with the oil. I didn't hear it run before I bought it (maybe a mistake) but the owner said that it ran fine. His mechanic said that it needed head gaskets because the water pump stopped working (?). The car sat for about a month and a half,before I bought it. Anyway I bought the car and drained the oil/water mix, put in fresh oil and tried to start it to get it into my garage. It started only with half throttle and a lot of cranking. After it finally started it would only stay running with lots of throttle, and ran rough and backfired below 2000 rpm. Got the LIM gaskets replaced and the problem still exists. No coolant is getting into the oil, the spark plugs looked fine (no evidence of burning oil or excessive ash build-up). It still takes a long time and about half throttle and a lot of patience, to get started. I know that its rare that the head gaskets go out but I don't know where to start. Thanks for any reply.

You can start by checking codes, this will give you an indication of where the problem originates. This is the first time I have heard of a head gasket failure on an 2000 PAU, probably the result of some idiot who did not care, or who was totally unattached from the basics of care care. Evidently, you have a bad (contaminated by coolant) sensor that is causing the starting problem. Hard to diagnose this from here, without some further codes or info.

I can't remember the "p" number but it was cylinder 5 misfire detected. That was the only code that I got. The spark plug wire was bad for #5. I did not change the head gaskets because I didn't think that they could be bad, after all of the forum researching and info gathering that I have done. The LIM gaskets were definitely bad though. Even with one spark plug wire being bad, would it cause it to start so hard?

A little more info. When I was able to get it to run, I was able to get it to operating temp and it did very well at temp regulation. It would go up to 212f and then one fan would kick on, it would cool down to about 190f and slowly raise up to 210 or so, and repeat it over again. All of this is done while I am keeping it running at around 2000 rpm. Anything less than that rpm it would stutter, spit and backfire when trying to get it back up to 2000rpm. I have changed the fuel pressure regulator (no change) and will replace the bad plug wire. I have read of the CPS and ICM problems that these cars have. I don't know which one it could be or if I am going in the wrong direction. Could they have gone bad from sitting for a month + ?

Have you disconnected the MAF to see how it runs. What is the fuel pressure & TPS voltage? Normally, the CKPS & ICM will not go bad from sitting. Have you replaced any of the coils?

I haven't tried unplugging the maf yet, but I will. I will have to get a fuel pressure tester for fuel pressure and I will also check the tps voltage. Coils have not been changed or touched either. As far as the tps voltage is concerned, what voltage should I be looking for?
I have an OBD II reader that can tell me the throttle position. As I move the throttle, it shows a smooth linear increase (in percent) and decrease as I go back and forth.

TPS voltage should be .45V @ closed throttle & show a smooth linear increase up to WOT where voltage should be 4.2v - 5.0v. Normally, one cylinder misfiring will not cause a starting problem. I assume you erased the original P0305 code (#5 cyl misfire) with the scanner after changing the wire(s). Do you have any other codes? Have you checked all the vaccum lines & fittings? How about the IAC, is it clean & working properly?

Have you checked coil output with a spark tester, for each cylinder?

Have you pulled the plugs and checked them? Are they worn or fouled? Are they A/C Delco's?

Are the coil terminals corroded?

Ok I changed all of the spark plug wires and it made a world of difference. It will actually start a lot easier than before. It still runs rough and will barely idle. Checked codes and got a p0300 multiple cylinder misfire. Changed the spark plugs and it started the same. Still runs rough and exhaust smelled like it still has raw fuel going through. Took off the coil packs and ICM and took them to autozone and they all tested fine no problems. I have also changed the pcv. I did unplug the maf and a p0102 code came up (while running). It didn't make any changes in the way that it ran. I then pulled the map sensor plug and got a p0107 code. No changes in the way that it ran either. The plug wires have been the biggest improvement yet. The iac has not been checked yet. The 2 torx screws that hold it in are very hard to move for that small of a screw. I'm trying to keep it from breaking off in the throttle body. Will keep trying though.

More than likely, you have a bad coil (or coils). Random misfire (P0300) can be set with one bad coil. As previously suggested, you need to use a spark tester for checking the coils output, I would not depend on AZ testing.

You may want to check the compression, and do a coolant pressure test.

It sounds like you've got ignition. You could also check for fuel pressure, maybe check the injectors also.

I used a spark tester and all of the coil posts put out the same amount of redish/amber light.

Fuel pressure would hit a little below 50 psi with key on engine off and bounce between 40 and 50 when running.

Compression has not been tested yet. I plan on testing it tomorrow evening. Hoping that all of the cylinders are good.

Z,I notice in the posts that you mentioned cleaning and checking the IAC and there is no mention of checking it,he does mention the ICM.

I did clean the iac when I had the throttle body off. I couldn't get it off to make sure that it was actually working.
I think that I found the problem though. After testing compression on the front bank I came up with these numbers.
#1= 3psi
#3= 3psi
#5= 90 psi
I would assume that this would mean that I have the rare 3800 that actually has bad head gaskets.
I only did the front side because I was too mad to even do the back side.
Now I have to take the whole thing back apart and then some.

Wow, with 3-psi on two cylinders, you have something worse than a blown head gasket. It would take a bent valve on both cylinders, cracked block, or hole in the pistos to come up with those numbers!

I guess that I will find out when I get it apart. Is there any tips or things to look out for when taking it apart?

I finally got around to getting the engine apart. I was able to get the head off and found that the head gasket was in good condition, no cracked pistons or head, no burned valves or stuck valves. I turned the engine before I took the head off and all of the valves moved up and down. I don't know what else to do or look for. Everything looks fine.

Now I have gotten a little farther into finding the problem. After talking to my brother about the whole situation, he suggested turning the head upside-down and pour some fuel into the combustion chamber to see if it leaks. So I poured some gas into the head and filled it up past the valves and spark plug and the gas leaked out pretty quick from the 1 and 3 cylinders through the exhaust valves and didn't leak anything on #5. My question is : would a leak in the exhaust valve like this cause it to only get 3psi on these cylinders? Or is there more to this story? Thanks for all of the help so far. It's very appreciated.

Take the heads to an automotive machine shop for a complete analysis. Without the valves removed, there is no way to know what the problem is. It could be burned or bent valves, or damaged valve seat. Visual inspection is mandatory.