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Old 03-30-2012, 04:22 PM   #1 (permalink)
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Default Engine RPM acting up

I've been having two issues with the behavior of my engine RPMs:

1. When coming to a stop, coasting in neutral (or with clutch depressed), the tachometer will fluctuate between ~800 and ~1500. Shouldn't just stay at idle? The problem is worse when I'm at very low speeds right before I stop, it (sometimes, not always) dips down really low and the car ALMOST stalls. For a split second the car shakes and the lights on the dash flash. Besides this being annoying, I don't want people in parking lots to think I'm revving my engine at them.

2. When driving and trying to accelerate, if I give it a lot of gas (not necessarily flooring it, but more than regular acceleration) the RPMs go up pretty high, near red line if I'm on the highway or something. Then it will go back to normal when I let off the gas. It's behaving kind of like an automatic car would except that I'm not downshifting which is what an automatic would do. I was under the impression that in a manual it should just gradually increase RPMs as speed increases.

I cleaned my MAF and IAT sensors and they were dirty but that didn't help. Other things to note are I have an Injen CAI, a Unichip Piggyback (to prevent CEL), and Magnaflow Cat-Back exhaust. The CAI and Piggyback however were installed before I bought the car so I'm not very familiar with them if they might be causing the problem. Any suggestions for either of these issues would be much appreciated, thanks.
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Old 04-04-2012, 12:23 AM   #2 (permalink)
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bump
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Old 04-04-2012, 01:13 AM   #3 (permalink)
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Have you checked your vacuum hoses? It sounds like a vac leak.
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Old 04-04-2012, 03:44 AM   #4 (permalink)
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spark plugs?
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Old 04-04-2012, 07:53 AM   #5 (permalink)
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How old are the O2 sensors? This is exactly what the engine does just before they go out.
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Old 07-10-2012, 05:31 PM   #6 (permalink)
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ok i realize it's been a few months but i finally got around to getting this stuff checked out so i figured i'd follow up. i went to the dealership (probably a bad decision, i think i got ripped off) and the first issue was because of the pcv hose that needed replacing. second issue was because the whole clutch assembly was worn down and needed replacing. makes sense now that i think about it. is it normal for a clutch to need replacing? its got about 95000 miles on it and been through a few different owners.

funny thing is my CEL never came on for any of this, the guy at the dealership was surprised about that. i'm pretty sure my "piggyback" is stopping it from coming on because i've never seen it come on unless the car stalls :/

anyway everything seems to be working now, thanks for your input.
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Old 07-10-2012, 06:27 PM   #7 (permalink)
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A few owners with THAT many miles...not bad! I had the same high revving while driving on the highway, when my clutch was about done.
I had mine replaced around 90k miles as second owner. I went with the mazdaspeed clutch though, alot more bite for my wild driving.

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Old 07-10-2012, 07:03 PM   #8 (permalink)
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PCV hose i common, i had to replace mine at about 100k, I did not get the surging issue but it did whistle because of it. PCV hose replacement is an expensive job at the dealer.

Diregard I thought i was in the 2.3 section. I guess you 3.0 guys have better access to the PCV hose.
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Old 07-11-2012, 11:19 PM   #9 (permalink)
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ok seems reasonable that i needed a new clutch and the new one is working great. problem is my tachometer is back to fluctuating again just like it used to. it was "fixed" for about a day but i noticed it's back again . i thought it was caused by the pcv hose? i'm gonna go back when i get a chance but do you guys have any idea what else could be going on?
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Old 08-05-2012, 12:34 AM   #10 (permalink)
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for anyone who cares, i ended up replacing my spark plugs (well 5 of them anyway, one of the boots was IMPOSSIBLE to pull out) and its been over a week worry free, no fluctuation on idle
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