'93 3.3 rough idle, stumbles off-idle

[manicmech]

I have a '93 Century with a 3.3 V-6 and 94,000 miles. It idles a bit rough, but stumbles really bad on acceleration from a standstill. Higher speed acceleration is normal. I got a code for a lean condition (44 I think it was). I replaced the fuel filter, air filter, and oxygen sensor with absolutely no change. It also has relatively new plugs and wires. I have about 35 psi of fuel pressure at idle. I do not have specs as to what this should be, but I thought it might be a bit low? Can anyone confirm what it should be? Could it be a MAP sensor? What else can I check? Thanks for any help you can offer, as my knowledge is mostly on older vehicles.

[richtazz]

Your symptoms are consistant with a bad MAF (Mass AirFlow sensor), but low/borderline fuel pressure can exhibit the same.

35psi fuel pressure is right at the low end of acceptable. The pump specs are 51 psi max, and on-car it should read 41-45 psi key on/engine off, and should drop 3-7 psi engine running with vacuum attached to regulator. So if you take the low KO/EO reading and subtract the max vacuum drop, you get 34 psi. Taking into account a margin of error on your gauge, you could be below acceptable pressure and in need of a fuel pump.

[Scrapper]

check your tps see if it's bolts came loose or need a new one.

[manicmech]

Thanks for the tips. I removed the MAF sensor, cleaned it, and reinstalled it with no change. The TPS is not loose. The fuel pressure with key on, engine off is 37 PSI, so I suspect it may be the cause.

[Scrapper]

yes time to drop tank.

[richtazz]

if ko/eo pressure is only 37 psi, then most likely the fuel pump needs to be replaced. It's only 4psi under minimum spec, so if you're using a cheaper/high usage pressure guage, it could still be the guage that is off but not very likely.