# rpm fluctuates



## calvinhobbes (Feb 1, 2005)

Hello:
I just bought a used 1997 Nissan Altima GXE with 54K miles on it last week and I have been noticing a few quirks. I am not sure if they are normal to all Altimas or if it is a symptom of an impending breakdown. First: the rpm varies a little bit between 700-800 rpm even when the engine is fully warmed up ( On my first car a 1989 Honda Civic the rpm would stay dead on 700rpm when fully warmed up). Second: With the car idling, when there is an extra load coming on like the AC compressor the rpm drops rapidly to around 550 rpm threatening to kill the engine down and then adjusts itself after a little while. I just noticed the rpms behave the same way even when I try to lower/raise the windows. Third: When I first bought the car, the acceleration from zero speed was pretty smooth. I recently had the drive belts changed and now when I accelerate from zero I can distinctly hear what sounds to me like a belt or someother rotating component whirring under the hood. Would appreciate any help/pointers on things to check/replace.
Thanks.
From Boulder.


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## KA24Tech (Feb 2, 2004)

Check the belt tension sometimes they get it too tight and it puts an unneccessary load on the bearings usually the alternator.
The fluctuation could be in the Idle Air Control Solenoid which gets dirty and sometimes will cause the idle fluctuation it could also be a misadjusted Throttle Position Sensor. Try unplugging the Mass Air Flow Sensor at the sensor itself next to the airbox see if it changes as well when it is running.

Troy


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## calvinhobbes (Feb 1, 2005)

KA24Tech said:


> Check the belt tension sometimes they get it too tight and it puts an unneccessary load on the bearings usually the alternator.
> The fluctuation could be in the Idle Air Control Solenoid which gets dirty and sometimes will cause the idle fluctuation it could also be a misadjusted Throttle Position Sensor. Try unplugging the Mass Air Flow Sensor at the sensor itself next to the airbox see if it changes as well when it is running.
> 
> Troy


Thanks for your reply. Before I start unplugging things like the TPS or the MAF (things I have never done before) can I check from the ECM output whether there is anything wrong with these components? I dont have the check engine light on. So does that mean there is nothing wrong with these components? Or does the Check engine light only turn on for catastrophic trouble with the engine? Also is there a way to read off codes from the ECM without a reader? The service manual says to check voltage from an appropriate ground for testing the MAF and TPS... where is the most suitable ground? 
-CH


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## KA24Tech (Feb 2, 2004)

I just check the ground side of the harness connection.
The codes can be read by accessing the ECU and turning the diagnostic mode screw. The directions are in the manual or on the side of the ECU. The long flashes are the first digits and the short flashes are the other set of digits.

Troy


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