fuel issue, severe. . .

[southerncross]

hey guys, before i go replacing things all willy nilly, i just wanted to ask if anyone has previously had this problem:

i noticed about 2 weeks ago my car started to hesitate up higher in the rpm range, like about 5000. i was going up a hill in second gear (and getting on it) and it acted like it was low on power. i wasnt sure what to think (it was the first hot day here in georgia) so i just figured maybe id just take it easy and check it later that evening. got it home, nothing seemed to be out of place or broken, so i waited for it to happen again. about two days later it was even hotter (about 88*) and it began under load about 4500rpm and absolutely would not rev past 5000 in gear under load. i took it out of gear and revved it, and it seemed fine. over the course of the drive it cut off twice, had trouble idling a couple times, and completely cut out maybe 5 or 6 times. . . as in no power whatsoever. i figured something major was going on so i babied it home, turning 2500rpm or less and taking it really easy, and it didnt happen. ive only driven it about 15 miles since then and as long as its cold (the engine) it has no problems. as soon as it gets to normal operating temp it starts this up again. this is my daily driver, so i cant just park it and tear it all apart. lucky for me, my ride to work is about a mile round trip daily, so i feel comfortable driving it that short a distance.

anybody have this problem before?

my initial thought was fuel, as in either a bad pump or bad injectors. i tried running some redline SI-2 injector cleaner through the engine, but it had no effect. i also thought maybe it was a bad tank of gas, but if that was the case it would happen even when cold, and its a little too weird of a coincidence that it hasnt happened while cold. my car has 92,000 miles on it and is on its second fuel pump. . . it is a used pump that came out of a car with 130,000mi approx. on it. i have already checked my ignition and that is not the culprit. im just looking for ideas and hoping one of you has had this problem before and can have a quick fix for me.

anybody have any suggestions?

[FaLKoN240]

What motor is it?

Mods?

Have you checked your sparkplugs?

[godsmack]

Need more info on your setup.

[southerncross]

yeah, sorry about that. i was just taking a break in between trips outside to post.

its a '90 5 speed KA24E, 90,000 miles. only mods to the motor are an intake, header, and exhaust.

i have not checked my plugs. i feel like a retard cause i probably should have checked that second or third. i swapped my maf out to a spare one i had and drove it around for a few minutes after it had gotten warm and i didnt notice any of the problems i'd had before, but thats just way to easy a solution, so im still not considering it fixed.

one thing ive been thinking about: the air intake sensor, the one that bolts to the airbox with the two small screws. . . one of the wires is broke on it, and i didnt realize it until i was under the hood today. does this thing really affect anything very much? ive heard people talk like its useless (which i have a hard time believing or else nissan wouldnt have put it there in the first place) and that a lot of them just unplug it and dont use it. im going to solder/heat shrink the wires back together on it just because, but the intake i have doesnt have a provision for it, so it is ziptied in the bay next to the air filter.