The Top Mitsubishi Galant VR-4 Resource

Join the best E39A 1991-1992 Mitsubishi Galant VR-4 community and document your GVR4 journey.

  • Software Upgraded - Reset Your Password to Login
    In order to log in after the forum software change, you need to reset your password. If you don't have access to the email address you used to register your GVR4.org account, you won't be able to reset your password. In that case, follow the instructions here to regain access to the forum.

Interesting idle surging - only when coasting in neutral, stops when parked

I initially had an issue with low idle/stalling and checked the ohms on the ISC and found it to be bad. So I bought a new one which fixed the issue. But now another interesting small issue developed but I want to correct. I have idle searching ONLY when coasting in neutral. It will idle between 1500-2000 until I come to a stop and drops back down to 800.

Anyone know why I would get idle searching only at cruising? What could be the culprit?

Car is not showing signs of vacuum leaks or boost leaks either.
 
Last edited by a moderator:

Check your FIAV, EGR (if you still have it), BISS screw, make sure your TB is closing all the way, and also check your o2 sensor.

There are not many other things after what I listed that will cause it.

Do go ahaed and check you vacuum lines, pop one off while idling and cover the hole with your thumb. If it gets better you fixed it.

One last thing, it's called idle surge, not search.
 

Thanks for the reply. Lol, I changed the title, thanks, I think I was searching so much I switched the words.

For the vacuum leak, I did already check that, and as I expected, no issues. It idles smooth when parked.

I'll have to check the FIAV, EGR and TB being closed. BISS doesn't look like it's ever been touched and from what I read, there is no need to adjust these correct?

For o2 sensor, other than getting an error code, how can you check them?
 

That depends, your car is 20 years old so things might need to be tweaked and tuned to get it running well.

What I listed are really the only things that can cause bad idle.
 

alansupra94

Well-known member
Joined
Mar 3, 2010
Messages
1,909
Location
Wayne,NJ
I noticed that I have this issue as well. It usually stays at around 1500rpm and varies a little. I personally believe it has to do with my Ostrich 2.0 as I have set my BISS 100% correctly, no vaccum leaks, IAC is fine and the EGR is removed. I don't really mind as it helps bump the alternator which I sure isn't performing to its peak ability.
 

If you are coasting and in nuetral your car should idle higher than if you were stopped. It's like that in most vehicles. It does not drop the RPMs all the way down to 750 when you let off because that can cause the car to stall. It is all written on vfaq in plain english.
 

Yeah, staying at a higher rpm (and varying slightly) is different than what I posted this topic about. In my case, there is a huge surge (1500-2000) while coasting. This occurs whether cold or warmed up.
 

ktmrider

Well-known member
Joined
Sep 10, 2007
Messages
3,128
Location
Tempe, AZ
Did you check your ECU before replacing the ISC? Many times a bad ISC will take out the ECU driver boards(s) and cause that kind of issue.

Also check the Closed Throttle switch, it can cause similar issues.
 

Lonewolf64

Well-known member
Joined
May 17, 2006
Messages
1,197
Location
Birmingham, Alabama
Have you unplugged the ABS computer situated in the trunk? If you have eliminated ABS but it is still plugged in it will cause this exact problem.
 

alansupra94

Well-known member
Joined
Mar 3, 2010
Messages
1,909
Location
Wayne,NJ
Quoting Red_Bird:
If you are coasting and in nuetral your car should idle higher than if you were stopped. It's like that in most vehicles. It does not drop the RPMs all the way down to 750 when you let off because that can cause the car to stall. It is all written on vfaq in plain english.



Figured that this was the case just had no proof and didn't really see the need to go searching for it.
 

Thanks for all the replies. I still have ABS (car is completely stock) and throttle cable is fine.

How does one go about 'checking' the ecu? Previous owner just changed it out with a new one (new from Mitsubishi...he actually went to dealership and bought it from them and had them install it).
 

hmmmm, does he have documentation that he did that. To buy an ECU new from mitsu and have them install it, I would think that you would need a second mortagae for that.

Make sure it's "new." Take it out and open it up, you can easily tell if something bad happened in there.
 

Yeah, I have the receipt as well, if I recall correctly, for $1200 or $1500 something. He wasn't a regular here and this was his spare car (drives an M3 for daily driving) so although I am sure he was shocked at the price, he just let Mitsubishi handle and fix the car.

But I will def check it when I go home as even a dealership can cheat people. If they happened to have a working used unit, I can see them just swapping that in there instead of purchasing a new one and make more money.
 
Last edited by a moderator:

grocery_getter

Well-known member
Joined
Jun 20, 2004
Messages
1,225
Location
Kent - industrial suburbs of Seattle, WA
All the other type of idle surging failure with the isc, fiav, throttle body plate not closing all the way, misadjusted biss will show up the same whether you are at a stop idling or you are at coasting with no throttle and in neutral. So those are not it. You said that it idles at a stop perfectly fine.

The problem happens in neutral no throttle coasting right? The only difference between resting at a stop idling with 0 speed and the condition that you are experiencing is that the car is not moving in one scenario and the other scenario the car is coasting in neutral? I would check speed sensor. In our case it is the reed switch in the back of the instrument panel. It is easier to switch out the instrument panel with another one with known working condition and see if that made a difference.

Or try using your cruise control for a good 2-3 minutes or more if you can. A good reed switch is critical to the cruise control function in our car. So if your cruise control still works perfectly then its not the reed switch.
 

Exactly, only while coasting (like coming to a stop light) in neutral does it surge. Once I stop, it continues surging for a second or two, then drops down to 800 rpm or so and stays steady.

Because of this, I too thought it was probably something speed sensor related, but the gauges work fine, and cruise control works great. I can cruise at a constant speed for hours (Just did a drive to Phoenix - 6 hour drive and had many long stretches where it was on cruise control).


BTW andre, great to see you still posting here. Not sure if you remember a chat we had a while back, but I have known you from back when I was into Hondas and you made the most beautiful 3" exhaust ever. /ubbthreads/images/graemlins/smile.gif I still remember your VR4 from back then and always wanted one since
 
Last edited by a moderator:

iceman69510

Turn Right Racing
Staff member
Joined
Mar 5, 2001
Messages
10,964
Location
Michigan
I may have missed this if already mentioned, but maybe closed throttle switch?
 

OMFGeofffff

Well-known member
Joined
May 5, 2006
Messages
867
Location
Burnsville, MN
I have this same exact problem. I'm not really sure why it's speed related.
 

1990ggsxnj

Well-known member
Joined
Nov 21, 2008
Messages
525
Location
Blackwood, NJ
I have this same issue with FIAV blockoff in two cars. Idle is solid and smooth but coasting in neutral gets a surge. I've been thinking of disabling the reed switch and seeing if the car can handle not stalling while coming to a stop. My thinking is it will be ok since the ISC is still functional.
 
Support Vendors who Support the GVR-4 Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications RixRacing RockAuto RTM Racing STM Tuned

Recent Forum Posts

Top