pimpman81

My car is acting really wierd! When I accelerate and let off of the gas my RPM's drop clear down to about 100 and then go back up. Another thing that it does is when im cruisin down the road and the car is about to shift gears (i have an auto) the RPM's jump up about 500 and then come back down to normal again. Im not sure why its doing this. I did the AC test where you turn it from off to maximum and my rpm's went up about 200 and then back down to normal. Can anyone help me on why this might be happening? Thanks

NZ Max

Daniel B Martin will help you.

SB97MAX

Ill bump this back up for you so Daniel Can see it. take care

Rit

iTrader: (3)

is it just a problem with with Tach. It would seem that the car would stall at 100 rpms, so I'd guess you should be looking for a electrical problem with either the tach pick-up, or the tach itself.

SMX

I have the same problem, took it to the dealer the computer did not find anything wrong. Its be like that now for 2 months, sometimes it does it other times its fine. I just ignore it now until I can figure what is wrong , other than that the car runs fine

pimpman81

Yeah, Took it to the dealership too and they didnt find anything. The car does go down to 100-200 and almost stalls and the steering wheel gets tight (like the cars off) then it goes back up. I dont realy know what to do. Daniel can you help? Thanks

Daniel B. Martin

Sorry, no. I read your original post and did not reply because I don't know what's wrong... don't even have a good guess.

Please understand that anyone attempting to diagnose a car problem at a distance is working under a handicap. In this case the dealer had the car and their fancy CONSULT electronic tester, but failed to diagnose the malady. You may have to wait for the symptom to increase in severity before the cause becomes evident.

If you don't want to wait and are sufficiently motivated to do something you could perform some basic diagnostic tests.

- Compression test (valves and rings)
- Intake manifold vacuum test (many things)
- Fuel pressure test (fuel pump, fuel filter, fuel injectors, fuel pressure regulator)
- Exhaust system back pressure (clogged Catalytic Converter)
- Fuel injector sound and resistance (fuel injectors)

Daniel B. Martin

I've got a guess. False air.

Any air which "sneaks" into the engine from a source downstream of the Mass Air Flow Sensor is called False Air. False Air will cause RPMs to increase. The first place to look is the flexible black plastic duct which conveys air from the Mass Air Flow Sensor to the Throttle Body. The engine moves around a bit on its flexible mounts during normal operation. If there is a crack or split in that air duct, engine movement may cause the crack to open and close. Every time it opens, RPMs go up. Every time it closes, RPMs drop.

Please make a careful visual examination of the air duct, and also make this simple test... with the engine idling, grab that air duct and push it back and forth, up and down. Don't use enough force to break it, but just enough to flex it as it was intended to do. If you can cause the idle speed to change, up or down, that is evidence of False Air.

Stillen_I30

I once test drove two I30s (used) one was a 98 and the other was a 97 and when i started both, the RPMs went up (liek they're suppsed to) and then shot down to below 500 for a second, and then went back up...all within a few seconds of starting. it was the strangest thing i ever seen...

SkyXRacer

Been trying to figure what the problem is for but 6 months now. But mine never dies. It jus drops to about 300-400 rpm everytime i press on the brakes to come to a stop and then it slowly goes back up to normal. But other than that my car drives fine.

PimpMan81 Please let me know if you figure out the problem.

emax02

iTrader: (1)

I think I know what is wrong with all of your cars. I had a very simalar problem and found the fix . The problem is most likely a clogged Throttle body{TOB}. Nissan's electrical diagnostics will not be able to figure this one out. The cure is to clean your TOB with some TOB cleaner, the stuff is like $3 a can and is very effective. Another thing I whould recommend is for you guys to replace your PCV valve, a clogged PCV valve will clog up your TOB with carbon and make your car run like it is{like crap}. All in all it will take about 1 hour and 15 bucks and your car will run perfect again . BTW even if this is not the problem you should do what I said anywasy since it's cheap and is good for the car. Let me know how every thing goes.

Confused

iTrader: (4)

this happens to me as well but it ONLY started after installation of the super charger. Could the idle air control valve - aux air control valve have something to do with it?

SkyXRacer

I've checked iavc and the aac valve with the ohm meter but it's fine.
Dunno what could be wrong.

MaxC1Get!

Instead of my RPMs dropping, they are raising intermittently. Sometimes it happens when I'm stopped at a light, put the car into park (auto), or start it up. The RPMs go up to 1200 for approx 10 seconds or so. Daniel suggested that it could be false air. However, I took it to the dealer and they said the computer couldn't find anything wrong. They decided to keep the computer hooked up and take the car for a spin. They still couldn't find anything. They asked if I use premium gas, and I said sometimes. Before I took it to the dealer I had the car filled with regular. I cannot recall if I've had the problem while using premium. Do you think the octane in the gas will make a difference? BTW, the day I took the car in, it was behaving. Since then, it is acting as I described earlier. Any thoughts!

Maury

iTrader: (1)

...and still test OK with the multimeter. i had a low idle immediately after cleaning my TB. i took the iacv housing apart and it was pretty dirty - it too tested ok on the meter, but i suspect it wasn't working to it's potential. now my car's running and idling great. just a thought- good luck
maury

Stillen_I30

I think thats the reason why my car idles rough. It drops significantly if i put on the headlights or foglights, and never returns to the set position of 650 RPMs. havent gotten a chance to take the thing off yet...will do that soon. Daniel, just a quick verification...do I remove the IACV using the two metal screws that are NOT fastened to the plastic part? thanks agian...

Daniel B. Martin

Correct. The factory service manual says ...

Remove idle air adjusting unit assembly (IACV-AAC valve is built-in) from engine. (The IACV-AAC valve harness connector should remain connected.) Turn ignition switch ON and OFF, and ensure the IACV-AAC valve shaft soothly moves forward and backward.

Stillen_I30

the damn batteries on my multimeter were dead, and were giving me a false value on the resistance test. threw some fresh batteries in there, recalibrated, and found the IACV-AAC to actually be 30 ohms resistance...problem of my RPMS dipping significantly when I throw on any accesories (esp. headlights/fogs) still occurs daily. I really have to find time to open that valve up and clean it...if it was dirty and stuck, would it still give a reading of 30 ohms?