92 240 sx sputtering/ rpms drop to 0 while driving. HELP!

[silvia2011]

ive had my 240 for a few months now, its got quite a few miles on it. Recently when i drive it it keeps loosing power. I will be driving with my foot on the gas and it runs good for the most part. BUT when i let off the gas the rpm gauge will drop to 0, sit there for a second then bounce back up and repeat several times till i put my foot back on the gas. the motor is still running when it does it but it just has me stumped now. ANY ideas? im checking the fuel filter current in a couple days when i go and work on it

thanks for checking out my post

[Mishkin_707]

does it do it when you push down the brake pedal? how's your charging system? alt, battery, grounds, maybe a vacuum hose is loose or cracked?

[silvia2011]

eh no it doesnt. the battery is good, alternator looks pretty damn old, which is what i thought it was. i checked the current for the fuel pump relay and it was right at 4.5, i dont know if thats low or not. and i will have to do a good check for vacuum leaks thats a good possibility

[r20crazy]

check for a vacumme(sp?) leak, also the IACV (idle air control valve), its on the back of the intake manifold [basically against the firewall] and very hard to get to may be cloged/malfunctioning..... try running some "sea-foam" thru the brake booster line..... but be warned.... this will created a HUGE HUGE HUGE smoke storm for up to 20 mins and car will idle crappy/stall if not reved or product fed to fast. if that doesnt work and no VAC leak found replace the IACV with a new unit or try ur luck with a junkyard unit.