up down rpm - Subaru WRX Forum
 
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post #1 of 7 Old 12-08-2009, 11:06 PM Thread Starter
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up down rpm

when the car is already warm and is not running mean waiting for traffic light you can see the rpm going up and down little bit and hear the engine up and down as well. Thank you guys for all these answer.
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post #2 of 7 Old 12-09-2009, 09:15 AM
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Could be a number of things. That only time something similar to that happened to me was in my 02 Cougar, the alternator was going out. Not sure if thats your issue, but check the electrical system (battery, alternator, ground).

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post #3 of 7 Old 12-09-2009, 04:55 PM
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Is your A/C on? Because if the compressor kicks in. Your engine will change RPMs when the compressor turns on and off.

Edit: A/C for your defrost.

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post #4 of 7 Old 12-11-2009, 12:15 AM
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I had this problem in my prelude. my intake manifold was really really dirty and all the sensors had dirt and crap on it. Its been a really long time but I think the MAF was in there and it was dirty to. if i was you i would try to clean out your MAF then see what happens. when was the last time you had your plugs changed?
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post #5 of 7 Old 12-11-2009, 07:15 AM
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A lot of people don't know that your defroster setting kicks on the A/C compressor, like mentioned above , I bet that is what you are experiencing.

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post #6 of 7 Old 12-11-2009, 09:15 AM
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What do you all have done to your car? How many RPM's does it range from? Look around for vacuum leaks as well, Have you ever had your car tuned before?
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post #7 of 7 Old 12-11-2009, 12:59 PM
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How much is it raising and dropping? Your IAC (Idle Air Controller) has a lot to do with that as well. If it's full of crap it will also cause your car to jump up and down in a cycle. It will run for about a second at 1500-2000 rpm, then bog down as if it were going to stall, then come back up for a second, then drop. Is that what you are experiencing? Or are you talking about more of a "load based" drop (i.e. when you're stereo is crazy loud, A/C compressor kicks on, power steering in locked position). Fill us in on specifically the issue you're having, and we can help a little more. The IAC is about $200-$300 but you can often take it out, clean it, dry it, and put it back in. On my old Prelude there was an adjustment to it which we had to change the first winter I had the car. If it's a load based drop, that's completely normal. Give us details on RPM levels and duration of each in the cycle and maybe we can help more.
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