Brief RPM dive when stopped.

gbrettin

I took my car up to Advanced Auto and had them test the battery. The battery has 313 cold cranking amps per what his machine said. I did a quick google search and the battery should be at 650.

Earlier today the temp was about 32 -35 degrees. It's now 65 degrees and the car is no longer dropping off time to time.

Maybe it's time for a new lightweight battery?

.... just remembered something.... I should check the water level in the battery.... bbiab

sunjian_auto

Had the same RPM dip together with slight batter voltage drop when rolling to a stop at neutral (idle drops from 650ish to almost 500 RPM) (mine is 6MT). After a month's trail and error I finally fixed it. Since my cause is different than the original post's, so i though of sharing it.
The RPM drop happened about 3 out of 10 times back when my car was completely stock, but I didn't bother to fix it. Then the problem worsen after I replaced the stock intake to Stillen G3 CAI. It happens almost 90% of the time and I finally decided not to be lazy and treat her right. Thanks to Z family's posts I listed the potential causes and rearranged them in the order of least to most workload:
1) Gas: I used to getting gas from Costco. So I switched to Chevron. Nothing changed after 2 full tanks.
2) MAF sensor: cleaned it throughly and still nothing changed.
3) ECU reset: I thought the RPM drop might be caused by not resetting ECU properly during my install. But i don't want to go thought the hassle to reset power window, radio, service reminder... list goes on. To avoid all that, this is what I did. Most people have seen the crazy "cheat code" and here is one example: ECU reset
(post #6 by cdoxp800). Tried it but still nothing changed.
4) Throttle body: I was trying my best to avoid this since my CAI requires me to take the front bumper off (yea, once again being lazy). But with options running low I ended up cleaning the throttle body. I used this as my guide: DIY Clean your Throttle Bodies - MyG37
I was surprised how dirty mine are for the millage I have (45K miles). Got lucky and problem fixed!!! Now is day 3 since the fix and haven't had RPM dip with or w/o AC on.
5) O2 sensor or MAP sensor: luckily I got my problem fixed by #4. Otherwise I would of gone through the hassle to put the stock on and take it to the dealer hoping whatever they can find will be covered by warranty.

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hooey_b

I've got the g37s, and I was having a similar problem, battery just changed. Try using seafoam for your fuel injectors and vacuum system, as well as cleaning out your upper intake manifold.

My car runs like new again.

gbrettin

So.............. The water level was really low. I'll let that marinate for a day or so and check back.

I'll also clean the TB's next week.

DEpointfive0

My battery is brand new, and worse comes to worse I have an even newer OEM battery
No tune either.


I'll try the TB thing this weekend. Can I drench the TBs in cleaner?

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gbrettin

I'll check with my brother to see how the TB's should be cleaned and let you know. My bro is a master mechanic with 20+ years exp.

DEpointfive0

I know the ideal "book" way, but if I cna disassemble them enough and just sonicate them in something. I'd rather do that.


Don't know how much I need to take off though.

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critical

i just used a micro fiber and some general cleaning solution. you'll see how dirty they are. just need to remove the intake tubing, or get it out of the way-pretty easy diy.



did this a ways back. it was always in drive at idle accompanied by a voltage drop. problem solved.

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gbrettin

I just got back from my brother's place and talked to him about it. He said it's probably dirty TB's. He pretty much repeated verbatim what Critical said.

1.)Take the TB's off
2.) Spray a micro fiber rag with TB cleaner
3.) Wipe it clean.

Super Werty

pull them off and clean them with maf cleaner/electrical cleaner

The spraying power from the can should be enough to blast any grim off with ease. no need to scrub or marinate anything

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DEpointfive0

It's still gonna vibrate like a mother with an auto though... ;-(

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gbrettin

I don't give two sh!ts about the vibrations. I just don't want my charging system to be strained.

Jordo!

It's quite possibly the battery.

Failing that search for an intermittent vacuum leak -- the unmetered air will cause you to skew lean at idle; ECU will compensate with high positive fuel trim, run rich, and dip a bit as it attempts to work around the leak.

So much of the throttle on this car is done with VVEL, I doubt cleaning the TB's will fix. Probably not it.

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TheRipperZ

I have that same problem then it started to turn on the oil light at the same time and then about 2 sec goes back to normal yesterday i bought a battery thinking it was it and nope it continue to do it. But the oil light did it when i changed my oil and theres no leaks i checked the dip and it was fine. I am loosing my mind help people!!!

Jordo!

Your ECU might be losing its mind... I'd check to see if have a bad oil pressure sensor if you aren't burning oil or actually losing pressure somewhere in the system... That might require a trip to the stealership and use of CONSULT III.

On that note: Do you have an oil cooler, either OEM or aftermarket?

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