I've been lurking in this forum for the past few weeks as I've undertaken, and just completed, a UIM/LIM job on the wife'* car, a 95 Bonneville SE, K engine, NA with about 187,000 mi on it. She'* an fiercely independent type, so I've always let her handle the maintenance details through her favorite mechanic (GM. Goodwrench auth.). I've monitored her and tried to educate her on how she might be getting screwed over on occasion (I think she'* had way too many transmission and coolant system flushes), but for the most part she'* done a good job of keeping up with repairs, etc. However, since she'* recently lost her job, these duties have fallen to me. And, since I've just purchased a house, I must wrench! It'* been over 25 years since I've done much of that. Enough background...
Looking back I should have paid more attention when she complained of having to add coolant. But she'd just had a water pump done, so I didn't think too much about it, except to keep me up to date. Well, she left for town one Saturday morning and the car just died, she said, on the way into town (2 miles away). She rolled it into a parking lot and called me to say it wouldn't start, it wouldn't even turn over. When I got there, I found it would just start to turn over. I tried to jump it, even though lights looked strong. No effect. I towed her home and layed on the starter until something started to make a whining sound that slowly increased in pitch. I let off quickly.
I found this site and investigated the hydrolock issue. A rachet on the crank bolt would not budge. I removed the front spark plugs and got it to budge about 10 degrees by hand. I took out the rear plugs and #4 (a little hard to turn all the way out) dumped about a cup of coolant. With all plugs out I cranked it successfully, blowing water out of all the cylinders, it seemed from the splash pattern.
Hydrolock, without a doubt. I drained the oil (it was quite low) and put in fresh oil and cranked it a little to work it in. I drained the coolant and put in new plugs (41-606) and gave it a couple of unsuccessful, but very short, cranks. The third one fired it up; idle surged breifly (about 1500 rpm) then dropped to about 900 rpm. I listened for less than 10 seconds for any unusual sounds, then shut it off. It sounded smooth and even, with no knocking or ticking sounds. So...
I bought the APN replacement UIM, and the aluminum LIM gasket set, as well as both radiator hoses, and coolant bypass elbow. I'd never been this deep into an engine before, so it took me longer than you seasoned gearheads, but it was very educational. I took pictures along the way, but nothing you guy haven't seen before. When I removed the UIM there was a lake of coolant sitting on the lower intake manifold; but, to be sure, I probed the UIM in the area of the EGR entry port and found the plastic material to be severely degraded (like thick, wet cardboard) with a small (about 3/16") hole easily discoverable. The LIM gasket looked OK, though.
The throttle body certainly needed cleaning, but I did not do a full disassembly of it. By this time I'm wanting to get this job done. I did spray through the front screen with a MAF cleaner, and I tried to avoid getting any throttle body cleaner past the throttle plate from the other side, though I think I was not entirely successful in that effort as certain areas of the screen turned out to be somewhat golden in color, probably from dirty TB cleaner.
Now, I had purchased the FSM from Helms, so I'd been following it faithfully, and saw no reason not to continue to do so in the refilling of the coolant system. I cycled ignition to on (no crank) a few times to get the fuel system going and used a series of short cranks to start it up. It seemed reluctant to stay running for the first few attempts, then it stayed running (I never touched the gas pedal). I was rewarded with the expected thick white smoke out of the exhaust for about 5 minutes, then all clear. Long story short, it seemed to take a long time for the thermostat to open, but it got to the point where it was open and only coolant flowed from the bleeder.
To the nitty-gritty (finally
)--It seems like it'* missing at idle, except that that it'* extremely regular and at too slow a rate to be a regular miss. When I give it a little gas it'* a lot smoother, then rpm drops back to just under 1000, like it'* supposed to, but right them it takes a brief dive, like it wants to die, but it catches itself back up for between 1 and 2 seconds, then dives again. It will do this over and over again like clockwork. I put it into reverse (no gas) to roll back a few feet so I could clean up the floor underneath, and it didn't die, but the pulsing was quite evident--the same when I pulled back forward.
I've spent hours over the past few weeks reading messages in this forum, and have caught some talk of O2 and MAF sensors and the IAC valve, but nothing that seems to address my issue in particular. Can anyone help me understand what is likely happening in my particular case? Thanks in advance to anyone who has read this entire message--and I'll put my second-born in the mail to anyone who can help me solve this problem.