240sx problem RPM dipping

[sickchick]

93 240sx auto trans 133,000 miles
This has happened a few times, once coming off the highway, a few times in city driving. When I come to a stop at a light, my RPMS have dipped from between 6000-8000 quickly down to below 4000, sort of like a stutter. I thought it would stall, so I shifted to neutral and it became steady again. It also occasionally takes a few seconds to catch when I start it in the morning.
I was told that 240s are prone to moisture sensor problems. Could that be to blame? Or any other ideas? Maybe just a tune up? It's been 20,000 miles since my last.
I'd appreciate any input- I know next to nothing about cars and can't find a trustworthy mechanic. Thanks!

[D-Bo]

do you mean 600-800 down to 400??
or are you driving the piss out of your 240??

[sickchick]

Oops. I'm officially a stupid girl. I guess I meant 400.

[D-Bo]

mine does it too when i shift to neutral coming up to a light and let the rpm go down but i drive a 5spd..

[SHIFT_KA24DE]

hrm.. that sounds very similar to my car. I drive a 5-speed so it's not big of a deal since nuetral is only a kick away. anyway, sometimes this happens when you have the AC turned on... so if you're really worried about it... try not to turn that on. when the ac compressor is turned on it puts additional stress onto the car so the possibility of it dying will increase.

i'd say it's fuel related problems. Try checking fuel injectors, fuel filters, fuel pumps, etc...

btw... you said your last check up was 20,000 miles ago?!! it's been a while hasn't it? unless you meant 2,000. It's ideal to do light maintenance like changing engine oil + oil filter every 3,000 or 3 months (whichever comes first). You could try using an additive called fuel injector cleaner on your next fill up as well.

[driftking777]

does your car idle rough when you first start it? kinda like it has alittle miss...like runs fine stutters runs fine stutters...ect...if so your valves might have some build up on them...and possible could need some work...but then again...

[lucki17]

hmm, i kinda had the same problem, now im in debt 3k.
i have an 89' auto and the speedo didnt work when i bought it, no big deal i thought, 2 days later it started to idle really low, 200-400rpm and it wouldnt shift right at start up, once i started driving it, it would get up to speed really slowly, but once it warmed up it was fine. well 3days after that it wouldnt shift into any gears at all, it just stalled out when i put it in gear. shitty, its been 3 months of it sitting in the trannie shop and mechanics and they just now found out it was the speedo, i have to get a new one from nissan.
but yeah, point of the story is get it checked out before it goes wrong in a major way. like mine.

[D-Bo]

mine starts and runs fine but i think the idle rpm is lower than it used to be.. even a couple of months ago.. i get my oil changed every 3 months, so did the 2 owners before me (between 3 and 6 months) is there any reason for a lower idle rpm?

[nissanfanatic]

Check AIV, fuel filter, and idle adjustment. www.240sx.org FAQ.

[sickchick]

OK, just got back from vacation and saw your replies, thanks.
I took my car to a mechanic and explained the problem, but when they took it out for a test it didn't happen for them, so they didn't do anything about it. The next day it happened again. Would it be wise to take it back and ask them to clean the injectors? I didn't have the a/c on, so it can't be that. I'm just trying to prevent breaking down on the road.
Also, I asked them to tune it up, told them it had been 20,000 miles since my last. They didn't seem to think it was necessary. Is there a set amount of miles when it should be done?
I love this car, it was a hand-me-down (I'd NEVER buy a sporty car with an auto trans), and I'd like to keep it going as long as possible. If anyone can give me some pointers, I'd appreciate it. Thanks.

[D-Bo]

when was your last oil change?

[sickchick]

I got my last oil change about 2K miles ago. That wouldn't be a factor, would it? And what is an AIV valve?

[D-Bo]

depends on the service history.. does it drive smoothly?? do you feel any significant restriction from the engine when you're driving?

[nissanfanatic]

The AIV is located on the driver's side of the engine bay. It runs between the exhaust manifold and the intake before the MAFS. It should have a small black box on it. Take the metal piece apart. It should come in half and have two sets of reeds in it. You may need to clean them with carb cleaner.

Another problem could be a vacuum leak. Check all of your vacuum lines. Typically the small one between your BPT and EGR will develop small cracks. Good luck.

[ExTrEmEDrIfT]

umm sounds to be a tranny problem since it does even out and is ok in neutral so if i would think that it would probably be the torque converter or the torque converter clutch..