Recent Topics
Do all shocks have oil or some oil in them?
by JLawrence08648. 10/23/18 08:10 AM
2014 Hyundai Santa Fe, alternator probs or not?
by Robster. 10/23/18 07:23 AM
Mobil Delvac - 3 options?
by Wreckage. 10/23/18 06:41 AM
Help my Maxima... Badly sludged up
by dexterbb. 10/23/18 06:38 AM
Duramax L5P UOA
by oakaro68. 10/23/18 05:54 AM
High moly grease and tapered roller bearings
by wrcsixeight. 10/23/18 04:22 AM
Interesting set of mods on a mid 90s Commodore
by Shannow. 10/23/18 02:48 AM
adding natural slippery chemicals to engine oil
by OilUzer. 10/22/18 11:04 PM
Vacationing alone
by WhyMe. 10/22/18 10:54 PM
This is great
by Marco620. 10/22/18 10:40 PM
Mahle Care Metix vs Mann Frecious Plus
by slacktide_bitog. 10/22/18 10:09 PM
Kia Sorento oil change capacity
by Roger7142. 10/22/18 09:30 PM
PP 10W-30, 5qt Jug $3.85 @ AAP
by Veilside. 10/22/18 09:15 PM
Use 0W-40 M1 Euro in 2012 Vette?
by NewC6. 10/22/18 09:12 PM
Napa Gold cut open
by ZZman. 10/22/18 09:07 PM
Will Castrol ever have 5w30 in a A3?
by Kjmack. 10/22/18 08:55 PM
Newest Members
dexterbb, KSG2308, PRY4SNO, 85fleetwood, brndn2263
66277 Registered Users
Who's Online Now
101 registered members (94astro, ARCOgraphite, 1foxracing, aba4430, 2009Edge, 10 invisible), 1,512 guests, and 32 spiders.
Key: Admin, Global Mod, Mod
Forum Statistics
Forums67
Topics292,407
Posts4,878,963
Members66,277
Most Online2,494
Oct 17th, 2018
Donate to BITOG
Previous Thread
Next Thread
Print Thread
Hop To
Diagnosing rough idle #4725027
04/12/18 07:16 PM
04/12/18 07:16 PM
Joined: Jan 2014
Posts: 452
Australia
Spetz Offline OP
Spetz  Offline OP
Joined: Jan 2014
Posts: 452
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 07:38 PM
04/12/18 07:38 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 07:39 PM.

1999 Mitsu Galant ES-V6 339k

Re: Diagnosing rough idle [Re: Spetz] #4725065
04/12/18 07:56 PM
04/12/18 07:56 PM
Joined: Apr 2018
Posts: 425
Somewhere in time
Imp4 Offline
Imp4  Offline
Joined: Apr 2018
Posts: 425
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 08:14 PM. Reason: Spelling, etc

2001 Mitsubishi Galant 2.4 - 157k+
Grandma's creampuff...
Re: Diagnosing rough idle [Re: Spetz] #4725097
04/12/18 08:13 PM
04/12/18 08:13 PM
Joined: Sep 2015
Posts: 1,553
USA
mk378 Offline
mk378  Offline
Joined: Sep 2015
Posts: 1,553
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 08:14 PM.
Re: Diagnosing rough idle [Re: Spetz] #4725113
04/12/18 08:25 PM
04/12/18 08:25 PM
Joined: Apr 2018
Posts: 425
Somewhere in time
Imp4 Offline
Imp4  Offline
Joined: Apr 2018
Posts: 425
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 - 157k+
Grandma's creampuff...
Re: Diagnosing rough idle [Re: Spetz] #4725125
04/12/18 08:38 PM
04/12/18 08:38 PM
Joined: Jan 2014
Posts: 452
Australia
Spetz Offline OP
Spetz  Offline OP
Joined: Jan 2014
Posts: 452
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 10:34 PM
04/12/18 10:34 PM
Joined: Mar 2011
Posts: 1,842
CA
spackard Offline
spackard  Offline
Joined: Mar 2011
Posts: 1,842
CA
Motor mount?

Re: Diagnosing rough idle [Re: Spetz] #4725306
04/13/18 12:37 AM
04/13/18 12:37 AM
Joined: Jan 2014
Posts: 452
Australia
Spetz Offline OP
Spetz  Offline OP
Joined: Jan 2014
Posts: 452
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 05:14 AM
04/13/18 05:14 AM
Joined: Jan 2011
Posts: 2,753
N.Ohio
Lubener Offline
Lubener  Offline
Joined: Jan 2011
Posts: 2,753
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 05:15 AM.

The "thinking" man's friend.
Re: Diagnosing rough idle [Re: Spetz] #4726737
04/14/18 12:50 PM
04/14/18 12:50 PM
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 12:54 PM
04/14/18 12:54 PM
Joined: Jan 2008
Posts: 10,821
OH
SatinSilver Offline
SatinSilver  Offline
Joined: Jan 2008
Posts: 10,821
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™