'91 Corsica 3.1 engine surges

My vehicle acts like it is running out of fuel yet throws no codes ..........if I am light on the throttle it is "reasonable", stomp on it and it's like
nothing is wrong, but medium throttle it acts up, surges. I've tested fuel pressure and put in new filter:OK, threw a timing light on it and no loss of ignition, EGR tests fine, even verified grounds are sound.. I know it is fuel injected but it acts like a carb engine with float level set to low, running lean. If I rapidly pump the throttle (like an old accelerator pump) it works fine. Any suggestions my friends??? Tom the ticket tearer
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Check ignition system, verify you have no carbon tracing, or leakage (use a spray bottle of water to mist the spark plug leads at night in the dark) if the plug wires are old or original, replace them. Pull a sparkplug, what does it look like? Does it have a distributor and coil? If so, replace cap and rotor and consider replacing the coil.
With the cost of plug wires, a cap, a rotor, and a coil, you can replace all of them for about $60 and if they have never been replaced since the car was new one of them is most likely shot. Some people would say to replace the plugs too, but in my opinion the nuisance of replacing them in most transverse engine mountings really only justifies it at 80,000 mile intervals, unless the engine has been suffering predetonation in which case once you fix the source of the predetonation you must pull all the plugs and check for cracked insulators.
Ted

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Here's the short list: Check fuel pressure running at off idle. You should have 80 PSI at the Schrader valve
Clean your fuel injectors.
Clean your throttle body.
Check or change your plugs
Check or change your plug wires
If all else fails change the Pressure Regulator. Charles
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Thanks for your suggestions, here is what I have done to date: Yanked plugs, regapped and wires recently replaced......resistance within 10% across the board....... Cleaned and checked all grounds ....... Replaced injectors with used ones:same symptom ........ Fuel pressure: book says 41-47 psi:, I'm righ there...so that's ok..... Cleaned throttle body: no change..... Blew out and checked all vacum hoses: OK but same same.... My symptom doesn't care if its cold or hot, so same same even when in open and closed loop...... However, I'm kinda thinking pressure regulator (too)......makes sense as it is "throttle" connected......through the vacumn line which is coupled to the intake manifold sensor ........... This is my personal vehicle which I keep in exceptional shape .......so with no codes the ECM is saying all is well........hell, I even checked timing to see if it was getting retarded from faulty knock sensor....nope, thats stable as well......... If this was a carb engine I know that holding a rag over it would richen it up and it would run fine, so that is why I'm leaning towards fuel starvation...has all the classic symptoms..........just where is going to be the headache...... Tomorrow I'll unhook the vacumn to the pressure regulator and give it a spin.......never can tell..........will let you all know what I find out.......but keep on sending suggestions....... Tom is tearing out his hair
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Found it, fuel pump was the root of the problem: was fine cold, when warm it would act erractic. Had to make a test line and tapped of shrader valve where I could watch it in "realtime". Thanks for the tips ........
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