Sorry to keep starting new threads- here is an update on the so far unsolvable stumble problem!
1.6l 4speed - will accelerate fine if pedal pressure is smooth and slow, but when you NEED to get to speed quickly (highway on-ramps, merging, emergency maneuver) the car jerks and shakes like there is no fuel flow (at WOT) then if you let off to half throttle and smoothly accelerate, then you have the power back and no shudder or stumble whatsoever! Here are the checked items: injectors, fuel pump, fuel pressure while running, temperature sensor (replaced since it was less than $20) oxygen sensor (unplugged and it made no difference) airflow sensor (cleaned) also have checked the EGR valve and it is currently disconnected and vacuum hoses sealed on both ends. The EGR valve itself was working properly- checked at idle with a vacuum pump, and it functions correctly. Whether the EGR control is working is debatable, but irrelevant since the EGR valve itself is not hooked up and is closed properly according to the test I did at idle. The PCV valve I was considering as a possible source for a vacuum leak? Anyone have any comments on that? I just found some forums discussing PCV valves causing lack of power when clogged or stuck open? I figure it's overdue to be changed anyway, so it will be getting a new one. I looked for vacuum leaks initially with a can of ether, and I plan to take apart the plastic intake box/intake hoses and carefully inspect them for cracks. In the meantime, if anyone has any suggestions, feel free to chime in! Thanks so much, -robbie