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#4498704 - 08/26/17 01:31 PM Idle randomly dipping
mclasser Offline


Registered: 04/13/13
Posts: 2233
Loc: The Northeast
This is in my Pilot.

90% of the time, the car idles at a solid 750 RPM at a traffic light with all accessories off. But the other 10%, the idle dips to like 600-650. When this happens, the engine makes a rumbling noise and you can feel the center console shake a little. BUT...turn on the headlights or A/C, the idle rises and everything smooths out again. It's strange that this happens intermittently. Car drives great otherwise.

Any ideas what could be going on?
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#4498794 - 08/26/17 03:57 PM Re: Idle randomly dipping [Re: mclasser]
bioburner Offline


Registered: 09/19/16
Posts: 1418
Loc: Minnesota
Maybe the 5 year old battery is starting to fail and the alternator is having to engage more to keep the system at 13 or so volts.
Many cars the AC system still exercises to keep seals good even with the switches off.
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#4498800 - 08/26/17 04:06 PM Re: Idle randomly dipping [Re: bioburner]
mclasser Offline


Registered: 04/13/13
Posts: 2233
Loc: The Northeast
Battery was replaced earlier this year; connections are all clean & tight.

In addition:

- All fluids are clean & full.
- I mainly use BJ's gas but fill up at Top Tier stations every 3rd tank or so to keep things clean.
- Inspected the air filter. It's 25k miles old but light still shines through; manual says to change every 30k.

I'm thinking about cleaning the MAF sensor & TB. I don't expect them to be dirty at only 45k miles but maybe it'll make a difference.
_________________________
2018 Hyundai Elantra VE -- 3K
2013 Honda Pilot EX-L 4WD -- 55K
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#4498840 - 08/26/17 05:19 PM Re: Idle randomly dipping [Re: mclasser]
gathermewool Offline


Registered: 01/09/09
Posts: 6002
My Civic will idle rough (haven't heckled RPM) after being fully warmed up and at higher ambient temps. This seems to coincide with the ELD sensing low electrical load and lowering supply voltage to 12.6 or so.

Turning even just the running lights on (all but headlights on) will raise the voltage to normal. The vibration doesn't go away completely (likely something else is the root cause of that) but the the vibrations do lessen.

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#4498855 - 08/26/17 05:39 PM Re: Idle randomly dipping [Re: mclasser]
JamesBond Offline


Registered: 12/13/06
Posts: 843
Loc: midwest
Maybe it's the cooling fans or ac kicking on. Try cleaning the throttle body.

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#4498965 - 08/26/17 08:49 PM Re: Idle randomly dipping [Re: mclasser]
FordBroncoVWJeta Offline


Registered: 04/16/16
Posts: 769
Loc: KS
Might be time for a new intake sensor.
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#4498990 - 08/26/17 09:33 PM Re: Idle randomly dipping [Re: mclasser]
ATex7239 Offline


Registered: 01/19/17
Posts: 331
Loc: Texas,USA
Go get the battery, alternator, voltage reg, etc. checked anyways. Sometimes you get a bad battery. Autozone with do it for free.

I've had bad or fouling plugs give me a rough idle, as well. Might be good idea to check those out and test the coil packs.
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#4501727 - 08/29/17 08:42 PM Re: Idle randomly dipping [Re: mclasser]
4ever4d Offline


Registered: 01/02/10
Posts: 953
Loc: North Carolina
Check the IAC valve. They will get dirty and cause idle issues. Throttle body cleaning will sometimes cause this problem also.
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