Rough idle after WOT

sladey121

sladey121

New Member
Lately my car has been idling rough after wide open throttle.. It idles at like 500rpm for a few seconds then cuts out fully. Other times it idles as if its on a cold start.. I work at mitsubishi so ive already scanned it but no cods were present.. Reset ecu but still doesnt seem to want to idle..

Any suggestions guys?
 
people pay 100's of $$ for a bit of lump so embrace it :lol:
 
Dunno about CH's but it was the idle motor in my CC that was buggered when it wouldn't idle properly. $250 later and all good.
 
my CH has a minor wobble in the idle, enough that you notice it but doesn't affect driving. usually sits around 850-900RPM and drops 50 or so the rises back up giving a barely noticeable shudder. does that sound like something yours did previusly?
 
Mine is similar StarGrinder not that I've taken too much notice but there is a slight shudder (1-2 at a time). My RPM is never consistent, sometimes 800-900, other times at 700 (mainly between 750-900), though more recently I've noticed that during the colder weather it's dropping down to 550-650 sometimes and almost tries to stop :(. Tbh havent really bothered much about it though
 
Found it was my valve clearances that needed adjusting. Intake vavles are tight causing them to ride when up to running temperature.. Going to adjust them next weekend, so fingers crossed thats what the problem is!

Just so you guys know, 4g69 2.4 litre, the vavle clearances should be adjusted every 60,000kms.. Using a 20mm (intake) and 30mm(exhaust) feelers guages, get car warm. Remove rocker cover. Find TDC, adjust every cylinder thats a too of stroke, rotate engine 180 degrees, adjust all others..

Pretty simple really.
 
sladey121 said:
Using a 20mm (intake) and 30mm(exhaust) feelers guages,
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Might want a decimal point in there lol

Bit unusual for solid tappets to 'tighten up', normally they become sloppy.
Good luck with it.
 
No no decimal there mate. Looked up workshop manual at work for my car. You have to adjust them while its hot unlike most valve clearances you do when cold.. Hence metal expands when heated..

And well no, just will tighten from multiple things.. Just when they are cold the clearance is finw but when hot, the clearance is off
 
Your tappet clearance will be 0.20mm inlet & 0.30mm exhaust when the engine is at running temp.

Cold tappet settings are not a desirable method, as it can not guarentee clearances once up to temp.
For example: The workshop manual for the 4G9X's lists cold & hot settings.
If the engine is new or has been altered, the cold setting is used to start things off.
Then re-checked once upto running temperature.

-Back to your original issue: when the engine is playing up at idle, does it still drive normally once a few revs have picked up? and maintain a slow speed easily with minimal throttle?
"Normally" if the valves are so out of tolerance your engine wont idle, the car will be a pig through the rev range.
 
If the engine is new, the valve clearances will have been adjusted electronically, and under normal circumstances you should have to adjust it.

20mm, and 30mm is 2cm and 3cm of clearance respectively - i dont think even your airfilter would have that much free play......
 
Wow just realised what i was saying haha! Yeah definatly .20 and .30mm...

I work at mitsubishi and on tritons, we adjust them every 30,000kms.. Have to do it when engines cold too
 
Mine is similar StarGrinder not that I've taken too much notice but there is a slight shudder (1-2 at a time). My RPM is never consistent, sometimes 800-900, other times at 700 (mainly between 750-900), though more recently I've noticed that during the colder weather it's dropping down to 550-650 sometimes and almost tries to stop . Tbh havent really bothered much about it though
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might just be a thing with that motor.... i'm getting mine serviced shortly, still just deciding where i'll take it.

Just so you guys know, 4g69 2.4 litre, the vavle clearances should be adjusted every 60,000kms..
Click to expand...

mine has just hit 64,000, was just over 60k when i bought her so I spose she's due for this.
 
I bought mine at 6xxxx and i doubt it was done, now has 120,000 and only just beginning to need to do it badly. Good ol' motor haha
 
I ran a bottle of that engine cleaner/octane raising magic goop through mine, for a couple of tanks, that idle wobble disappeared but came back after a bit.

I am wondering what would happen if I fueled her on 95 or 98 for a tank or two.... other than going broke of course :p
 
at the rate my fuel economy, I only run 91 (standard ULP) but never E10 though.
 
probably a conversation for another thread but, i've always wondered about the pros/cons of running 98 over 91. i mean, in a 50 litre tank.... its another, what? $5-8 a tank? I suppose the real question is, is there ~$60-80 a year (if you average a tank a week) worth of benefit in running 98?
 
StarGrinder said:
probably a conversation for another thread but, i've always wondered about the pros/cons of running 98 over 91. i mean, in a 50 litre tank.... its another, what? $5-8 a tank? I suppose the real question is, is there ~$60-80 a year (if you average a tank a week) worth of benefit in running 98?
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Everyone I have spoken to about this says that their car runs noticeably better on 98, and responds more quickly to throttle position.
 
Its not rocket science really, higher octane rating = bigger bang = less fuel compared to 91 octane to create same bang = better fuel economy.. Ive noticed around 50kms more per tank compared to 91 octane.
 
Its not rocket science really, higher octane rating = bigger bang = less fuel compared to 91 octane to create same bang = better fuel economy.. Ive noticed around 50kms more per tank compared to 91 octane.
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thats actually not quite right sladey, but you're on the right track

Higher octane doesnt make a bigger bang, it makes sure the bang occurs at the right time. fuel combusts under a specific set of circumstances, what upping the octane does is make sure that that combustion doesn't happen too early. You are essentially upping the precision of the circumstances required to cause combustion in the cylinder. in cars that can run 91, it means that 98 will usually improve the response (as mentioned by jamente) and economy as mentioned by yourself.

but yes, I am considering making the switch. for the sake of another $50 or even $100 a year on petrol, seems like it could be a worthwhile investment..... just gotta make sure that if my dad borrows her and decides to do me a favour, doesn't end up watering down my tank :p
 
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