Go Back   AnandTech Forums > Social > The Garage

· Hardware and Technology
· CPUs and Overclocking
· Motherboards
· Video Cards and Graphics
· Memory and Storage
· Power Supplies
· Cases & Cooling
· SFF, Notebooks, Pre-Built/Barebones PCs
· Networking
· Peripherals
· General Hardware
· Highly Technical
· Computer Help
· Home Theater PCs
· Consumer Electronics
· Digital and Video Cameras
· Mobile Devices & Gadgets
· Audio/Video & Home Theater
· Software
· Software for Windows
· All Things Apple
· *nix Software
· Operating Systems
· Programming
· PC Gaming
· Console Gaming
· Distributed Computing
· Security
· Social
· Off Topic
· Politics and News
· Discussion Club
· Love and Relationships
· The Garage
· Health and Fitness
· Home and Garden
· Merchandise and Shopping
· For Sale/Trade
· Hot Deals with Free Stuff/Contests
· Black Friday 2014
· Forum Issues
· Technical Forum Issues
· Personal Forum Issues
· Suggestion Box
· Moderator Resources
· Moderator Discussions

Thread Tools
Old 12-03-2011, 12:13 AM   #1
Senior Member
Join Date: Nov 2009
Posts: 340
Default Causes of rough idle?

I drive a 1990 Toyota Camry with a V6. 160k miles. On my way to the airport 2 days ago (bad timing), it started idling rough. When under way, it sounds and feels normal, but at idle the engine runs rough and the speed blips up and down quickly. It feels like maybe it is not running on all cylinders, but that's a wild guess. I had two cylinders go out on a different V6 car once due to a coil pack dying, and it sounded way worse, so I'm guessing it is only one cylinder out if that's the case. Also, oddly, I hear -no- difference from normal at speed. Sounds absolutely identical to before the problem.

It started at least once normally after the problem emerged.

The car is waiting for me in an airport parking lot an hour from home tonight. What should I check first?

Thoughts: arc tracing on distributor cap, borderline spark plug, bad/clogged injector
Heat: Ned Funnell
Formerly a lifer. Came back for FS/T.
Ned Funnell's blog
nedfunnell is offline   Reply With Quote
Old 12-03-2011, 12:18 AM   #2
Golden Member
pandemonium's Avatar
Join Date: Mar 2011
Location: Augusta, GA
Posts: 1,463

Most commonly is the O2 sensor.
..:: |We are but shadows of our achievements and dust of the stars; empowering the universe to have conciousness.| ::..
..:: |Fighting ignorance is bliss.| ::..

If you're curious about getting into vaping, I'd be glad to help! I quit smoking with vaping! /truestory
pandemonium is offline   Reply With Quote
Old 12-03-2011, 12:42 AM   #3
exdeath's Avatar
Join Date: Jan 2004
Posts: 13,478

Vacuum leak, idle valve, open EGR, etc, are all things that will affect idle but be insignificant (problem goes away and engine smooths out) when the engine is revved or operating at normal driving speeds and during acceleration. Idle hunting is usually a clear sign of a vacuum leak or slow responding idle control valve.

Bad ignition components will also manifest as cruise and acceleration hiccups as well but it's never a bad idea to replace plugs/wires/cap/rotor if they are old and you observe excess erosion or arcing. Arcing in the distributor cap is a sign of too high resistance in the plugs/wires.

Just recently, for example, the cause on a brother-in-law's Saturn was a $20 intake manifold gasket on a 1.9L (vacuum leak on cyl 1 causing a lean misfire at idle). Problem found by spraying carb cleaner around intake sealing surfaces and listening for the rough idle to smooth out.

Last edited by exdeath; 12-03-2011 at 12:52 AM.
exdeath is offline   Reply With Quote
Old 12-03-2011, 12:43 AM   #4
LTC8K6's Avatar
Join Date: Mar 2004
Location: Under an American chemtrail
Posts: 18,938

IAC valve...my pat answer to idling problems.
no offense, but does he have some sort of mental dissability? -nick1985

Brainwashed, mentally unstable, and stupid Intel user, screwed by Intel and located directly under a chemtrail.

Don't be a moron! Buy AMD!
LTC8K6 is online now   Reply With Quote
Old 12-03-2011, 10:05 AM   #5
natto fire
Diamond Member
natto fire's Avatar
Join Date: Jan 2000
Location: Ohio
Posts: 6,618

Originally Posted by pandemonium View Post
Most commonly is the O2 sensor.
Not sure about the newest cars, but all the ones I have worked on ignore the O2 sensor at idle.

I would check the idle air control valve, and for vacuum leaks as well. Do you have A/C? If so try turning that on and listening to the idle. Personally I would pull the IAC valve regardless and clean it with carb cleaner, there will definitely be some carbon buildup.
natto fire is offline   Reply With Quote
Old 12-03-2011, 11:35 PM   #6
Senior Member
Join Date: Nov 2009
Posts: 340

Thanks for the info, all. It started, idled, and drove normally tonight. Not sure what the story is on this. I've heard that some ignition issues only happen during higher humidity, so maybe that's a factor. Anyway, some more info:

Reasonably new plugs and wires (judging by that they're clean and bright, installed by/for the PO). Cap looks newish as well.

EGR valve bypassed- vacuum line plugged. It's been running fine this way for half a year, situation normal. I'll check to see that the plug hasn't fallen out, though. Is EGR usually active at idle?

Haven't checked the IAC at all, but I will.

I looked over the vacuum system a few weeks ago just out of curiousity, and I didn't see anything abnormal.
Heat: Ned Funnell
Formerly a lifer. Came back for FS/T.
Ned Funnell's blog
nedfunnell is offline   Reply With Quote
Old 12-04-2011, 09:32 AM   #7
jlee's Avatar
Join Date: Sep 2001
Location: AZ
Posts: 45,728

It could've been moisture in the distributor cap - would explain why it cleared itself up in time.
Heat 91 MR2 Turbo 07 GX470 Sport
jlee is offline   Reply With Quote

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT -5. The time now is 08:06 PM.

Powered by vBulletin® Version 3.8.8 Alpha 1
Copyright ©2000 - 2015, vBulletin Solutions, Inc.