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Hunting Idle on Hot Start is driving me nuts!

cheekychimp

Well-known member
Joined
Apr 19, 2004
Messages
7,333
Location
East Sussex, U.K.
Okay I previously started a thread on my idling users here.

Click

A lot of the issues are now solved so I am starting this thread to concentrate on the remaining issue which is: -

On cold starts despite having to be turned over a few times before it fires, it starts fine and idles really, really well but it hunts badly and stalls on hot starts if switched off for 15 minutes or less. I cannot for the life of me figure out why. I have heard that there is some sort of code in the ECU for hot starts. What does that incorporate and could it be causing any issues?

To recap this is an S90 throttle body which has no provision for a closed idle switch which is currently disconnected. I am using an FIAV block off plate and it has been suggested that this could be leaking. The throttle body may need to be grounded as I think the OEM grounding location was lost when we switched throttle bodies. Finally since the ISC is old it could be faulty. I purchased a new ISC but it seems the JDM and USDM ISCs are different so I am stuck with the old ISC at present.

Any of these issues could technically be the source of the problem but I really need to know why any of them would only cause an issue on a hot start and not on a cold start.

Anyone got any ideas?
 

jepherz

Staff member
Joined
Aug 8, 2004
Messages
7,877
Location
KC, Missouri
You might as well test the coils of the ISC if it's old and you're questioning its reliability. Just do the ohm test and if any of the coils are open or shorted out, you know it's not going to work correctly.
 

cheekychimp

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Apr 19, 2004
Messages
7,333
Location
East Sussex, U.K.
SouthCali ... I have absolutely no idea mate. What is it, what does it do and where can I find it? Please tell me more because whilst I do still have a few things to check like the ISC this does appear to be a hot start specific problem.
 

SouthCaliVR4

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Joined
Jul 31, 2010
Messages
984
Location
North county San Diego
if you trace the vacuum line from the fuel press regulator it should go through a vacuum solenoid. I believe the theory is to boost fuel pressure on hot starts. later when I have time to look it up I'll dig up more info & the diagram. This is a part I'm unsure whether or not it's applicable to the jdm version but I would think so.
 

cheekychimp

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Joined
Apr 19, 2004
Messages
7,333
Location
East Sussex, U.K.
Sounds like a reasonable assumption on your part. I'll check that out. Assuming that part is there on the JDM vehicle and assuming it is FUBAR'd, what symptoms could I expect?
 

cheekychimp

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Joined
Apr 19, 2004
Messages
7,333
Location
East Sussex, U.K.
Okay the solenoid us not currently in play. I have an AFPR and it bypasses the solenoid. Is this likely to be the issue? Seems that a lot of people set things up like this without issue but since I assume the solenoid was installed specifically for hot starts it seems suspicious.
 
Joined
May 30, 2011
Messages
7
Location
Pampanga, Philippines
Thanks for the useful info, but i am about to try your solutions re: idle probs. if i will block the fiav and isc with a plate, will there be any new problems that may come out after this modification on a 4g67 dohc engine? what would i do with the wire harness of the isc? thank you again for all the help.
 

dlesser

Well-known member
Joined
Jun 26, 2011
Messages
61
Location
Westminster, CO
I just finished blocking off my FIAV today and it solved my problem. I had idle surge really bad and I simply followed this little guide.

click

My problem is fixed and it is really not hard to do. This is a good place to start because you can always change it back quickly and you don't need to buy anything :)
 

GSX_TC

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Joined
Apr 7, 2011
Messages
3,722
Location
Houston, Texas
so all you did was rotate that valve clockwise and that got rid of your idling problem?
 

GSX_TC

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Apr 7, 2011
Messages
3,722
Location
Houston, Texas
ah ok, so if its the ISC this will do nothing for you then huh
 

dlesser

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Joined
Jun 26, 2011
Messages
61
Location
Westminster, CO
So, yeah this just closes the FIAV. You can also screw it back out to the same position as long as you count the amount of turns it took to close it. I have about 3 working ISC motors that I was able to test with so I quickly figured out it was the FIAV.

Someone please correct me if I am wrong but the idea behind idle surge is that too much air is getting through the throttle body at idle. The ISC motor can compensate so my theory was to just remove some of that "passing air" by blocking off the FIAV. Now the GVR4 idle's better than my EVO /ubbthreads/images/graemlins/cool.gif
 
Joined
May 30, 2011
Messages
7
Location
Pampanga, Philippines
I have done it.FIAV Shut! as you said no more high idle on cold start. good idle but have to adjust it to 1k rpm to compensate when i turn on the a/c. Could you also help me re: 4g63 gti camshafts, would it fit to a 4g67 engine(1.8l disp.). Or 4g63t cams will fit on a 4g67? Are all the parts of the4g63 the same with 4g67? (Difference only is the size or bore of the pistons?
Thanks again for all the tech infos and how to dos.
 

AnotherNewb

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Joined
Apr 25, 2010
Messages
1,472
Location
Orlando, FL
Just adding my two cents. Blocked my fiav and isc off on my throttle body. No longer does it stall when I stab the throttle and die. Idle doesn't hunt or sound labored. Im happy with it. Every dsm I own from now on will have the fiav and isc blocked off. Oh yeah, instead of buying one I made one out of a steel outlet cover. Took me ten min and 6bucks.
 

Quote:
re: 4g63 gti camshafts, would it fit to a 4g67 engine(1.8l disp.). Or 4g63t cams will fit on a 4g67? Are all the parts of the4g63 the same with 4g67?

click
 

GSX_TC

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Joined
Apr 7, 2011
Messages
3,722
Location
Houston, Texas
Today I blocked off my fiav like that link said, but nothing changed. Idle still surges and if left on long enough it just dies. Would a bad ISC be the cause of those symptoms?
 

dlesser

Well-known member
Joined
Jun 26, 2011
Messages
61
Location
Westminster, CO
From my experience it sounds like your ISC is not working correctly (especially since your FIAV is blocked off). Do you have anyone near you with a spare? I can ship you one that I know works if you want...

I don't like to toss parts at a car but it is a simple test if you have a known to be good ISC motor.
 

GSX_TC

Well-known member
Joined
Apr 7, 2011
Messages
3,722
Location
Houston, Texas
Ok I just put on one of those good black ISC's and now it's even worse! Now even with the biss set all the way clockwise it's revs and surges very quickly around 2200. So even with a blocked off fiav and working ISC, it still doesn't work. In fact it's worse. Any ideas?
 

GSX_TC

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Joined
Apr 7, 2011
Messages
3,722
Location
Houston, Texas
Quoting AnotherNewb:
Just adding my two cents. Blocked my fiav and isc off on my throttle body. No longer does it stall when I stab the throttle and die. Idle doesn't hunt or sound labored. Im happy with it. Every dsm I own from now on will have the fiav and isc blocked off. Oh yeah, instead of buying one I made one out of a steel outlet cover. Took me ten min and 6bucks.



You make it sound sioo dam easy but it's not. Bevause that's not how easy it is
 
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