Why would re-starting make a difference??

My 89 Supreme has been running good for months now...no problems to worry about...then, all of a sudden the following happened:
Last Tuesday, I was doing a lot of running around, stop and go driving
etc. I got home, dropped some things off and ran back out to run some more errands. I started the car, and the second it started-up I could tell something was wrong. It was surging up and down, bogging, felt like it was misfiring etc. The SERVICE ENGINE light was going on and off. The engine vacuum was only like 8" hg instead of the usual 17" hg. So I turned it off, ran inside to call my friend to tell him that I would be late, ran back outside, turned the engine over, and it ran PERFECTLY!!!??
Than 2 hours later, I was leaving a grocery store and it did the same thing again! This time, without shutting it off, I decided to just drive it to my house(because I was only like 2 minutes away) so that I could grab my Scanner to see what was going on with it. I get home, and accidentaly shut if off without first grabbing my Scanner. And, guess what, I started it BACK up and it was running GOOD again!!! This got me really frustrated.
Anyways, it hasn't done this since. I checked the codes and the only one I got was 33 which is MAP Sensor Voltage HIGH. BUT, I'm 99% sure that this code occured because of the LOW engine vacuum due to the ACTUAL problem, and is not the MAP Sensor itself. Even AllData says that a code 33 will often occur if there's any vacuum leaks or misfires etc.
So here's my question. Why in the heck would simply re-starting the car make a WORLD of difference?? This make absolutely NO sense to me at all.
I mean, it can't be ignition related, because that wouldn't all-of-a-sudden be cured by re-starting. I don't think it could be a fuel problem because of the same reasoning.
The ONLY thing I can think of is an intermittent MAP Sensor giving false BARO readings to the ECM. In other words, I know that the MAP Sensor is used to tell the ECM what the outside barometric pressure is so that it can compensate for changes in altitude ie. lower altitute results in more fuel and vica-versa. So, if the MAP was telling the ECM that I was somewhere around the height of Mt. Everest, the ECM would try to compensate by taking away a whole lotta fuel...
Anyone!?
THANKS:)
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It could be any of the things you mentioned plus a bad injector that operates intermitently (been there, done that) or a worn shaft on the TBI that knocks the TPS off and sends erroneous info to the ECM (been there, done that too).
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bigbossfan80 wrote:

In my 1987 LeSabre, it was a bad MAF sensor. Also, the timing gear was almost in pieces, so it would run okay for a while, then bad, then finally, a week or two later, not at all.
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I would look at the EGR system. The valve could have been open when it should have been shut. MU
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MarkU wrote:

That was busted too on my car. The combination of the three made for a nasty experience.
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Think about what parameters in the engine computer get reset at each key cycle or ignition start.
Although you aren't getting any ignition codes, I had a similiar problem an intermittent crank sensor. When the engine starts, it looks at the crank sensor pulses and goes into either bypass mode or the PCM controlled mode. An intermittent fault can cause the engine to run poorly or quit. A key cycle resets the default timing.
I also had this similiar problem with the TCC solenoid. It would unlock and only a key cycle would allow it to re-lock at highway speeds.
Rich
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Cam position sensor tells the ECM where number one is. After a few revs during starting, if the cam sensor doesn't signal, the ECM takes a guess, with a one in three chance of being correct. If I had to swag a part into this car, I would swag a cam sensor.
Jerry

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I would agree except that I can't explain why the owner didn't get any Cam sensor errors.
"Jerry Newton" <figatmcttelecom.com> wrote:

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snipped-for-privacy@yahoo.ca (bigbossfan80) wrote in message

Map sensor does more than indicate altitude. Its primary role is to sense engine load (how hard the engine is working)by watching vacuum. Engine vacuum is directly related to throttle position, so high vacuum= closed throttle=low load. The more the throttle opens, the more work the driver is asking the engine to do, the more fuel is needed. So, map sensors have a huge effect on pcm fuel calculations. An intermittent map sensor could cause the problem you describe. Some of the other responses could be right, but I think if you had a bad crank or cam sensor (even intermittent) you'd have a code. These ignition systems are also known to have issues with the ignition module (under coil pack) causing driveability problems. Sorry no real clear answer here, just lots of things to check.
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