Recent Topics
Anti-Counterfeiting packaging
by sloinker. 01/17/19 09:13 PM
Heavy Snow Predicted for Northeast Sat/Sun
by Donald. 01/17/19 08:34 PM
Pennzoil Ultra Plat 5w30 1.4L T Chevy Cruze 10k
by SubieBlue. 01/17/19 08:03 PM
Coated rotors
by supton. 01/17/19 07:51 PM
Good samaritan
by JLTD. 01/17/19 07:15 PM
Doing suspension work. Need alignment?
by HawkeyeScott. 01/17/19 05:45 PM
100mg CBD Cannabis Gel
by Al. 01/17/19 05:36 PM
Electric Car "Green Test"
by redbone3. 01/17/19 05:06 PM
Want to try a uoa
by Dylan1303. 01/17/19 04:56 PM
Happy Birthday, Betty White!
by eljefino. 01/17/19 04:20 PM
Fram Ultra for Ecoboost 2.7
by Purpfox. 01/17/19 04:10 PM
Idle Speed / 1998 Olds 88
by Mark72. 01/17/19 03:28 PM
Heat blanket for your oil filter!
by MrWideTires. 01/17/19 03:24 PM
Proper oil viscosities.
by Bullwinkle007. 01/17/19 03:20 PM
44$ for 5 gals of home heating oil treatment!
by Audios. 01/17/19 03:05 PM
Good job Hyundai!!!
by Andy636. 01/17/19 02:43 PM
PP 0W-20 vs PP HM 0W-20 - Difference in VI
by The Critic. 01/17/19 02:34 PM
Newest Members
Dickerson888, Frisky, polarisman340, jfradella, Bigyetti83
66964 Registered Users
Who's Online Now
117 registered members (2015_PSD, 209paulc, 40w8, 4WD, 2009Edge, 12 invisible), 1,643 guests, and 46 spiders.
Key: Admin, Global Mod, Mod
Forum Statistics
Forums67
Topics296,753
Posts4,958,231
Members66,964
Most Online2,577
Jan 14th, 2019
Donate to BITOG
Previous Thread
Next Thread
Print Thread
Hop To
Diagnosing rough idle #4725027
04/12/18 06:16 PM
04/12/18 06:16 PM
Joined: Jan 2014
Posts: 460
Australia
Spetz Offline OP
Spetz  Offline OP
Joined: Jan 2014
Posts: 460
Australia
Hi everyone,

My idle isn't as smooth as it should be.
I have replaced the usual culprits and have done all the usual tests with no result.

Would the best option be to take the car to a mechanic who has an oscilloscope to diagnose this?

Car is a 2003 Mitsubishi Diamante.
Items replaced:
Fuel filter, injectors serviced, ignition module, spark plugs, spark leads, distributor cap and button

Tests conducted:
Compression test, vacuum test, vacuum leak test, ECU and all sensor test (all sensors reading within normal parameters)


2003 Mitsubishi Diamante 6G74 3.5L. 5 Speed auto. 155,000 miles. Shell Helix Ultra 5W40 at 6k OCI
Re: Diagnosing rough idle [Re: Spetz] #4725042
04/12/18 06:38 PM
04/12/18 06:38 PM
Joined: Nov 2011
Posts: 292
Florida
BrownBox88 Offline
BrownBox88  Offline
Joined: Nov 2011
Posts: 292
Florida
My Galant has the 6G72 which isn't much different other than being a 3.0 motor. Did you check the idle air control motor and clean the throttle body itself? EGR and the EGR control solenoid can cause rough idle too.

Last edited by BrownBox88; 04/12/18 06:39 PM.

1999 Mitsu Galant ES-V6 339k

Re: Diagnosing rough idle [Re: Spetz] #4725065
04/12/18 06:56 PM
04/12/18 06:56 PM
Joined: Apr 2018
Posts: 631
Somewhere in time
Imp4 Offline
Imp4  Offline
Joined: Apr 2018
Posts: 631
Somewhere in time
I recently had this on a 2001 Galant 2.4 and the condition was worse with a cold engine.
I was able to diagnose a faulty IAC.
New through Rockauto was $175. I was able to hit up the local Pull-a-part and pickup two for $10 each. This was good thing because only one worked. But it did solve the problem for $20 invested.

IAC for your Diamante is about $120 on Rockauto, but seemingly much cheaper at $36 from 1aauto.com.
I would try to diagnose this condition on your car and pull one from the bone yard near you if it turns out to be the issue.

Last edited by Imp4; 04/12/18 07:14 PM. Reason: Spelling, etc

2001 Mitsubishi Galant 2.4 - 160k+
Grandma's creampuff...
Re: Diagnosing rough idle [Re: Spetz] #4725097
04/12/18 07:13 PM
04/12/18 07:13 PM
Joined: Sep 2015
Posts: 1,631
USA
mk378 Online content
mk378  Online Content
Joined: Sep 2015
Posts: 1,631
USA
Is the rpm correct? Use a service tach; the dash tachs are not very accurate especially at idle.

Also do a cylinder drop test to see if the misfiring is based in one cylinder or generalized.

Last edited by mk378; 04/12/18 07:14 PM.
Re: Diagnosing rough idle [Re: Spetz] #4725113
04/12/18 07:25 PM
04/12/18 07:25 PM
Joined: Apr 2018
Posts: 631
Somewhere in time
Imp4 Offline
Imp4  Offline
Joined: Apr 2018
Posts: 631
Somewhere in time
You could also check for a vacuum leak, the MAF sensor, or a coil that is going....


2001 Mitsubishi Galant 2.4 - 160k+
Grandma's creampuff...
Re: Diagnosing rough idle [Re: Spetz] #4725125
04/12/18 07:38 PM
04/12/18 07:38 PM
Joined: Jan 2014
Posts: 460
Australia
Spetz Offline OP
Spetz  Offline OP
Joined: Jan 2014
Posts: 460
Australia
Hi everyone,

I have cleaned the throttle body and MAF sensor too.

I connected a laptop with the MUT software which gave me all the readings and the rpm was as it should be an stable.
I reflashed the ECU to raise the rpm in D by about 80rpm or so which made the idle smoother but I didn't want to go up any more than that (I believe it is now at 700 from the original 620rpm).

I have also checked the EGR by blocking it off completely with a blanking plate and there was no difference to idle


2003 Mitsubishi Diamante 6G74 3.5L. 5 Speed auto. 155,000 miles. Shell Helix Ultra 5W40 at 6k OCI
Re: Diagnosing rough idle [Re: Spetz] #4725243
04/12/18 09:34 PM
04/12/18 09:34 PM
Joined: Mar 2011
Posts: 1,927
CA
spackard Offline
spackard  Offline
Joined: Mar 2011
Posts: 1,927
CA
Motor mount?

Re: Diagnosing rough idle [Re: Spetz] #4725306
04/12/18 11:37 PM
04/12/18 11:37 PM
Joined: Jan 2014
Posts: 460
Australia
Spetz Offline OP
Spetz  Offline OP
Joined: Jan 2014
Posts: 460
Australia
I can feel the engine jerk while I have my hand on it.
1 mount is new OEM (the roll stopping one that takes most of the force) and this has of course made the rough idle less noticeable but it is only masking the issue.

My original question is whether an oscilloscope will diagnose a rough idle?
I've booked my car in on Wednesday next week to get checked. Hoping whatever the issue is it is found


2003 Mitsubishi Diamante 6G74 3.5L. 5 Speed auto. 155,000 miles. Shell Helix Ultra 5W40 at 6k OCI
Re: Diagnosing rough idle [Re: spackard] #4725349
04/13/18 04:14 AM
04/13/18 04:14 AM
Joined: Jan 2011
Posts: 2,880
N.Ohio
Lubener Offline
Lubener  Offline
Joined: Jan 2011
Posts: 2,880
N.Ohio
Originally Posted By: spackard
Motor mount?

That's what I am thinking.I usually them them all together.

Last edited by Lubener; 04/13/18 04:15 AM.

The "thinking" man's friend.
Re: Diagnosing rough idle [Re: Spetz] #4726737
04/14/18 11:50 AM
04/14/18 11:50 AM
Joined: May 2005
Posts: 64
Nevada City, CA
G.Frost Offline
G.Frost  Offline
Joined: May 2005
Posts: 64
Nevada City, CA
Valve lash adjustment? Sometimes running PEA, combustion deposit detergent, like Red Line SI-1 will clean up a lumpy idle.

Re: Diagnosing rough idle [Re: Spetz] #4726741
04/14/18 11:54 AM
04/14/18 11:54 AM
Joined: Jan 2008
Posts: 11,090
OH
SatinSilver Offline
SatinSilver  Offline
Joined: Jan 2008
Posts: 11,090
OH
I remember someone on here recently trying all sorts of things that didn't work. But then they added a quart of Lubegard Red to the trans after doing a drain and fill. And voila much smoother idle.


BOB IS THE OIL GUY® Powered by UBB.threads™