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1G FIAV and ISC

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jpmxrider489

10+ Year Contributor
2,410
146
Apr 4, 2010
pittsburgh, Pennsylvania
I know there a plenty of threads regarding this issue. My car is idles around 2200 cold. Once warmed up it runs fine. The car is only driven in the summer and on weekends. I am also on SD and would like to think this issue happened after the switch but am unsure.I have the black isc and the resistance is 38-40 on it. This is my 3rd isc to troubleshoot. On a cold start my isc goes from around 100 down to 0 once warm. Which brings me to the fiav, could it be stuck or out of adjustment? I was thinking about taking out the freeze plug and turning it in to adjust it. For people that have done this, how hard is it to physically turn? I have read about it being stuck. I am ok with blocking it off but would rather not. Could it be my ecu is the issue? I can post a idle log when I get off work.

I have replaced the isc, checked for boost leaks, and properly adjusted the biss.
 
I recently tried to turn the FIAV plug and it was stuck so bad that the plastic was breaking as I tried to turn it, ended up buying the bypass plate to keep the IAC. Do you have any engine lights?
 
I did mine last month and it's fine. You should be able to rotate it even if it's stuck. I wound up buying a bypass plate for $12 off ebay and sealed it with some gasket maker just in case.
 
I did mine last month and it's fine. You should be able to rotate it even if it's stuck. I wound up buying a bypass plate for $12 off ebay and sealed it with some gasket maker just in case.

Trust me there was no moving it haha I even drilled deeper holes in the plastic to get more grip and it is broke away.
 
I had a spare that was junk, I did try and move it and it was stuck and broke off as well. I do not have any CELs. I attached my idle log. Its fairly long. If anyone can give me some advice. Also, since it runs fine when warm, is this a big issue? My throttle body is rebuilt not to long ago. Since you both did the block off plate. Why did you do it? Did it do what you wanted?
 

Attachments

  • cold start.elg
    219.7 KB · Views: 24
If the FIAV is leaking, it causes a vacuum leak that makes your car's idle impossible to get right. When you bypass the fiav with a plate, you can longer have that air leak, and you loop the coolant lines to the throttle body so that your intake air temps aren't as hot. Works great for me.
 
I had a spare that was junk, I did try and move it and it was stuck and broke off as well. I do not have any CELs. I attached my idle log. Its fairly long. If anyone can give me some advice. Also, since it runs fine when warm, is this a big issue? My throttle body is rebuilt not to long ago. Since you both did the block off plate. Why did you do it? Did it do what you wanted?
Just quickly going over it your log looks pretty normal to me. FIAV stands for fast idle air valve, its job is to make the car idle high on a cold start by allowing extra air in. As it warms less and less air bypasses the throttle until the idle drops to normal. Been awhile since I had a FIAV so can't remember how long it holds the idle high.
In the log once warm you're idling slightly higher than the target idle speed, and your iscpos is stuck at zero which means the ecu is commanding the isc to close completely trying to bring it down. Might have a small post throttle vacuum leak (could be from the fiav) causing this or the biss is out too far.
 
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In the log once warm you're idling slightly higher than the target idle speed, and your iscpos is stuck at zero which means the ecu is commanding the isc to close completely trying to bring it down. Might have a small post throttle vacuum leak (could be from the fiav) causing this or the biss is out too far.
I know the biss isn't supposed to be messed with, rather than set it and leave it alone. Ill have to look at it again, but from what I remember I went by the how to. Also what are signs of the ecu being what is bad regarding the isc? I have read about ecu sockets getting messed up. Ill do another boost leak test if thats what you think it is but for it to idle that high must be a big leak? I can set my target idle to be lower as well. Since setting the biss happens when the car is warm, I dont know if that is affecting how it is at a cold start up. So maybe it is the FIAV. Just thinking out loud here.
 
I know the biss isn't supposed to be messed with, rather than set it and leave it alone. Ill have to look at it again, but from what I remember I went by the how to. Also what are signs of the ecu being what is bad regarding the isc? I have read about ecu sockets getting messed up. Ill do another boost leak test if thats what you think it is but for it to idle that high must be a big leak? I can set my target idle to be lower as well. Since setting the biss happens when the car is warm, I dont know if that is affecting how it is at a cold start up. So maybe it is the FIAV. Just thinking out loud here.
What I meant was with a working fiav idling around 2000 on a cold start is normal. If the fiav is not closing all the way once warmed up it will cause a leak that does not show up with a BLT.
Setting your target idle lower isn't gonna do much since the iscpos is already 0 which is fully closed. Screwing the biss in should bring the iscpos up. If you end up with it all the way in and it's still at zero you have a leak. Here's a link that should have every answer you need.
http://www.ecmtuning.com/wiki/idlesurge?s[]=isc
 
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So after working on the car, I did actually find some boost leaks. My tb vacuum ports and 1 coupler. Ill attach another log. I do think the fiav is messed up but I think ill live with how it is because it idles fine when warm. If I ever have to take the tb off, ill just block it. I went over the idle switch and tps. I also adjusted the biss to get the isc decent. If you look at the log, isc is at 20 and lrnidladj is at 140. I had to use the tpsadjust but it goes to 100 where before it was 99. The tpsvolts is 65, i know 63 is ideal. I did end up changing the input for my wideband. I actually have a aem gauge but I couldn't get it to match link. So I just did the linear wb. The wb in the car and linearwb and afrest all match extremely close.

Few other points. My afr is around 13.7. I cant get it to idle at 14.7. No matter how extreme I adjust global, deadtime, or sd table, it always comes back to 13.7. Is this ok or how can I further move foward? My boostest doesnt match my aem tru boost controller. My gauge at idle is -17 not what link says. Also my cooltemp on my aemgauge is around 205. The sensor is in the upper rad hose. Is this ok or how can I fix it? Any imput would be great.
 

Attachments

  • warm idle final.elg
    63.9 KB · Views: 18
You need to fix the FIAV. You'll fix the idle and it will be jacked again the next week. It causes a vacuum leak and it needs to be fixed. It dealt with this for two years without knowing it was the FIAV.
 
It is not possible for the car to idle above 1500 if the idle position switch is working. You have one of possible several problems. A partially open throttle for any number of reasons including a possible sticky cable. A nonworking idle position switch. Or a missing ground on the throttle body to allow the idle position switch to work. I would start there. Anything over 1500 the ECU cuts fuel. If it doesn't the ECU does not realize the throttle is closed The post says 1G however the op has a 2 G. If I recall correctly the 2G uses a thrittle position to determine throttle closed
 
I had a spare that was junk, I did try and move it and it was stuck and broke off as well. I do not have any CELs. I attached my idle log. Its fairly long. If anyone can give me some advice. Also, since it runs fine when warm, is this a big issue? My throttle body is rebuilt not to long ago. Since you both did the block off plate. Why did you do it? Did it do what you wanted?

I did the bypass, not the block off plate. Just get the bypass plate with a new gasket, use a little RTV on both sides of the plate and call it good. That will eliminate one of the possibilities. Check your throttle plate to be sure it’s not partially open.
 
So I recently had the problem where the gasket on the bottom of my throttle body leak coolant into the throttle body and made it start 2 stick. I took the throttle body off cleaned it and put a new gasket. Also I noticed the previous owner had a small piece of metal over the one port I believe for the 1 valve. Anyway when I start my car the RPMs bounce very rapidly from 1000 to about 1500 RPMs. I replace the fast idle air valve and Gasket. If I didn't put the idle position sensor back in the same spot would that have anything to do with the idle problem I'm having?? Thank you for any help
 
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