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Rough Idle on Cold Engine

microserf

Member
Joined
Feb 11, 2015
Messages
7
Location
Manila, Philippines
hi
i am a car newbie here, my ride is a 1991 Mitsubishi Galant GSX, non turbo, DOHC. Recently I am having some rough idling upon starting the engine cold. The RPM drops to about 500 and if i try to drive it, i have to press on the gas pedal to keep the idle up to 1000, and it drives pretty unsteady. But once the engine warms up in about 20 to 30 min. It drives smoothly as if nothing is wrong. But the fumes out of my tail pipe smells like gasoline. and i have horrible gas mileage ( about 3 km per liter )


I went to a repair shop, they cleaned the IAC and throttle, and they suggest that my MAF needs replacement. So i got myself a surplus MAF (we dont have many OEM parts here specially for older models), which the mechanic assured me is working fine. After the installation, i still get the rough idling on cold starts, but the mechanic suggested a workaround - pumping the gas pedal 4 to 5 times before cranking the key ( after the check engine light went off). When i do this, the engine starts fine, reving at 1000 but it reverts back to rough idling when i dont do this. As before the car is fine when the engine is warm.

my question is
1. by pumping my gas pedal - what does it do to "cure" the rough idling? what condition does it create, so that the rough idling on cold starts will not happen

2. Did it cure my horrible gas mileage, since it has just been 3 days,i had no chance to confirm if my gas mileage has improved. i filled my car to full tank and will measure my gas consumption

thanks in advance
 

misterfixit

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Aug 4, 2004
Messages
1,596
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Fiav?

How long has the car been in the philippines? have the throttle body been bypassed on the coolant?
other one to check, if it's a GSx, it's a us import, does it still have the lambda sensor on it or has that been torn off?

Cheers,

Rich
 

AllanL

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Aug 4, 2008
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294
Location
NV
did they remove the throttle body to clean it?

i doubt that in was done ON the car...
 

microserf

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Joined
Feb 11, 2015
Messages
7
Location
Manila, Philippines
Hi misterfixit,
Thanks for the fast response.
Fiav, is this the same as the Idle Air Contoller or IAC? I never heard the mechanics here mention it, i will ask about it.
Actually, my car is a 1991 Galant Gti, but i am told it is sold as GSX in other parts of the world.
Regarding the throttle body been bypassed on the coolant, from what i understand from reading about it online, bypasses the IAC, right? I dont think this is the case on my car. I will need to ask about the lambda sensor. What does a lambda sensor do, i never heard of it before. Sorry, i am a total newbie.
 
Last edited:

AllanL

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294
Location
NV
on the car/engine or off of it?

did they disassemble the throttle body?
 

microserf

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Feb 11, 2015
Messages
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Location
Manila, Philippines
Hi they just opened up the throttle and cleaned it on the car, did not disassemble the throttle body. Is it better to disassemble it for cleaning?
thanks
 

AllanL

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maybe all the grime settled in the iac lower part of the throttle body...

this is why the manual says to cover the lower hole when cleaning the throttle body online [meaning on the car]...

pm sent...
 

cheekychimp

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Apr 19, 2004
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East Sussex, U.K.
Do you still have the gasoline smell from the tail pipe? Irrespective of the FIAV or IAC possibly contributing to your cold idle issues, it sounds to me as if you are running very rich. 3km per litre equates to about 150 km per tank. I get almost three times that 'mileage' (over 400 km per tank) on my VR4 here in Hong Kong. My 1989 GTi in the UK would probably do even better. Something is seriously wrong with your AFR in my opinion and that could very well be contributing to, if not causing, your rough idle. I'm surprised that pumping the throttle works though. If you are running rich, I'd have thought that would have made things worse.

Can you check your injector size, MAF serial no. and ECU number? Also do you know what CR your car is (no guarantee the stock pistons haven't been changed but if they haven't the engine no. may help here)? Later and earlier model GTis had different CRs. I'd be looking to check if you have the correct injectors, MAF and ECU for your specific engine.
 
Last edited:

AllanL

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GTis in the Philippines were:

4G63 NA with 250cc injectors, no knock sensor, no o2 sensor [just the rich-lean adjustment knob], 7-pin MAF with 6254 ECU...

came with either 6bolt or 1G 7bolt engines...

...most probably...

since MAF was replaced, may be a mismatch...
 
Last edited:

AllanL

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by the way, what happens when you turn on the A/C?

idle drops or idle goes erratic?
 

misterfixit

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Hi Guys,

The reason I asked if it was truly a GSX was to see if it runs closed, or open loop injection.

It will run like a sack of sh*t while warming up if not set right. It's a GTI running open loop (as Alan says no o2 no knock).

IAC is the idle servo. Now here's where it gets fun. It needs to get FIAV hooked up as well and set up. It's the ONLY way the car will run right open loop.

The FIAV is in the lower part of the throttle body (next to the servo), it must have coolant running through it. You must verify it opens and closes in hot water (preferably done off the car). Once this is verified good, then you must set the idle air (so the servo is at mid range on warm idle) then you must have the mixture adjusted.

Get a mechanic who knows Mitsubishis, preferably 4g63's and has a logger. Or log it yourself. I posted a thread about the FIAV, the pics were taken when I did my friends GTI here in Baguio about 2 years ago, I'm doing the same again on mine here in the PI too.

Hope this helps,

Rich
 

AllanL

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NV
hey Rich, betcha the IAC on your GTi was tan-orange with the rust...post some pics soon!

i pm'd him to contact some guys who know their GTis well...

disassembling the throttle body from the IAC might be the only way to get it right in this case, considering it was cleaned online, and with this issue as a result...
 

misterfixit

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Mine really flummoxed me, It's why I distrust most people calling themselves mechanics here. One coil was missing from the inside of the servo. when I took it apart.

The o-ring/gasket thing on mine is finished, and I believe that may have been the start of the cascade failure that led a previous owner to bypass it. But Allan, you should see the car. Throttle body really is the least of my worries!

Rich
 

tektic

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Dec 19, 2012
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ronkonkoma, ny
If it warms up it idled normally? How about a coolant temp sensor. If you can get a logger on it you can figure it out in a second. I always bypass the fiav. A bad isc could also be a culprit.
 

cheekychimp

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Rich,

Everything you and Allan have said makes sense but (assuming the issue still exists) I'm still struggling to see why this is causing such awful fuel economy, especially if after the engine has warmed up, the car runs fine as the OP suggested. Is all that fuel being consumed during the time it takes the car to warm up with the really rough idle, or could the fuel mixture be running continuously rich as a result of the condition you are mentioning?

One other thing, if as Allan said there is no O2 sensor, just a fuel enrichment knob, any chance that that has been incorrectly set?

Paul
 
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misterfixit

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Because here in the Phillipines, like the uk there is no feedback. Generally people do not rev their engines either, so Idle is just that..

It doesn't idle normally, there is a strong smell of gas at the tail pipe.

Tektic, yes in the US and anywhere where the Lambda sensor is present, you can bypass, as the fiav will be compensated by the closed loop of the ecu adjusting the fuel with minimal effect.

On my freinds car here, the issue was only discussed, when the whole lot go so bad a the idle could not be stabilised by adjusting the idle screw.

If the O.P. car is overfuelling badly, and runs rough on warmup. The FIAV, is effectively the switch between, warmup and warm. You can fool the engine into running when it's warm, but if the systems round it are messed up, it'll not behave when cold. The poor performance between both suggests their are other issues as well.

Would be worth checking the coolant sensor, but if that is an issue, I believe it'll throw a code (not sure here) I can't test it on mine as the car is torn down.

The overfuelling is because of some other issue that has been subject to 'remedyo'. I would suspect it will either be, or a combination of the following. Disconnected idle switch (with messed up idle settings), Mixture resistor set incorrectly, incorrect injectors. (mine had 190cc ones on it not 240cc)


Cheers,

Rich
 

cheekychimp

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On a more positive note and just to give all GTi owners (including the OP) some hope, my car in the UK is 'apparently' running like a champ. My Dad said he would run it 'gently' for me now and again, just to turn the engine over and rotate the tyres etc. I told him not to go too easy and reminded him that even old dogs need to stretch their legs a little. Seems that that was the only encouragement he needed. Now he drives it to his band practice every week (because it's a decent distance to drive regularly) and he has already taught some boy racer in some flashy Citroen a lesson. Apparently he was sat on Dad's rear bumper for three miles out to Beddingham, constantly blipping the throttle but never having the balls to actually overtake and then when they got to the dual carriageway and he floored it he actually didn't have what it took to beat some well put together 1989 Japanese engineering at full throttle!
 

microserf

Member
Joined
Feb 11, 2015
Messages
7
Location
Manila, Philippines

thanks for all your responses guys, i really appreciate the inputs.

@Paul Yes i still have gasoline smell out of the tailpipe but not as bad as before. Yes the mechanic who replaced the MAF said that my AFR was all wrong and adjusted it, he said it is now 70% air and 30% fuel. I asked the mechanic the same thing about pumping the throttle before startup, he said it is like a "system reboot"?? as some of the sensors are not in the ideal working condition.

as for your question on the car part specifics, i think AllanL is correct. and yes the MAF came from an Eclipse, the mechanic said.
If it is a mismatch, is there a way to "match"it?

@ AllanL - there is no idle drops when the AC is on.

@ Rich - thanks i will get another mechanic to look at the FIAV, if by logger you mean the diagnostics port, the mechanic i saw said mine does not work because all the wirings are messed up...i will get a second opinion. thanks again

@ tektic - yes if it is warmed up normally by 15-20 min, it idles fine. using the workaround by pumping the throttle 4-5 times before starting the engine works ok also. Coolant temp sensor was just replaced a week ago so it should be working.

@ Paul - to clarify...my awful 3 km/ li mileage was before the MAF was replaced, when i had the MAF replaced, the mechanic said that my AFR was all wrong and he adjusted it. I still have not verified if my fuel economy has improved or not, i will see in the coming days as i filled the car with a full tank to see how it goes.

Thanks guys for your feedback and kind words. i am currently down with the flu, so i cant go anywhere til next week. i will update this post as soon as i have the car in the shop. thanks again.

Jonathan
 
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