2.8 multiport has problems

Seems like I've been posting in here a lot lately but I have a problem I'm not sure what the symptoms point to.
'88 Cavalier Z-24, 2.8 mpi, 170K miles, has intermittent problem both
with hard starting and power loss.
Sometimes I go to start it and it will fire a time or two right away but then I have to crank it another 10 seconds or better without it firing at all, but I can always coax it into starting by manipulating the throttle.
Also, when I am driving it it will lose power and surge, then come out of it, etc.
It had a starting problem about a month ago and it turned out to be a leaking injector flooding the engine, which I replaced.
Within the last 25k miles, the car has had: New ECM new MAP sensor New TPS New heads, plugs & wires New intake gasket and injector o-rings
Also, since I thought the symptoms pointed to a faulty ignition module, I replaced that, but the problem remained.
Fuel pressure is about 36 psi with engine running, althugh I did note that the pressure remains there at any throttle position, and also with the vacuum disconnected from the fuel pressure regulator. I know this indicates a faulty regulator, but I don't think that would cause the symptoms (starting, etc.) seen here. Especially since the pressure holds steady with engine shut down.
I inadvertently left the MAT sensor unplugged after changing the ign module, and hence got a check engine light alerting me to that fact. I plugged it in and light went off.
I just checked the codes and got one for MAT sensor, naturally, and also one for "lean exhaust."
This has never had an O2 sensor replaced in the 6 years I've had the car. But I wouldn't think that would come into play with cold starting when the vehicle is in open loop.
The problem seems ignition related. Could a knock sensor go bad and cause the ECM to make the ign timing go crazy?
The EGR moves freely by hand and there are no codes for it.
Just wondering if anyone has any suggestions, TIA
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snipped-for-privacy@webtv.net (James Goforth) wrote:

The purpose of the fuel pressure regulator is to maintain a constant pressure differential across the injector tip. At 36 psi and 18" of vacuum, there is a 45 psi differential. At 36 psi and 2" of vacuum, there is a 37 psi differential. Certainly fits the no power and lean exhaust condition. Then again, it may not be the fuel pressure regulator that's causing the low fuel pressure as you describe, it could just as easily be a weak pump and 36 psi is all it can manage to begin with. Does fuel pressure go up when you pinch the return line? Have you done a fuel volume test? Does the engine start easier if you give it a squirt of fuel thru the throttle body?

As evidenced by a lack of spark when the problem is occurring?

You'd likely have ESC codes.

What's missing when it won't start? Fuel, air, spark, compression.
Have you Ohm checked the injectors? They are extremely notorious for shorted windings? Does the engine run any better if you unplug the alternator? (the small plug)
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Thank you for your input. After clearing the codes I drove the car around all day yesterday and most of the day before -- trying to get it to act up and perhaps set a code -- and it behaved perfectly normal. I am not done messing with it yet, obviously, I definitely want to determine if the fuel pump is getting weak, and I believe I have the specs for injector resistance, etc. Since it's my own car I guess I also have the option to wait and it will either get better or get worse. Ssince it's a convertible it will just be going into storage in another month or so anyway.
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The car finally exhibited the same behaviour as previously described. I didn't have time to look at any further than before, but after thinking about it --and this might be an important clue -- I am pretty sure it never acts up while i'm driving it, but rather only right after I start it up -- whether from stone cold or after just shutting it off to run in to a convenience store. It will always idle; just seems to lose all power as throttle is depressed. Today when it did it, I just let it idle for a few minutes and then it came out of it.
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