Possible bad ISC

[Crazyjoker77]

OKay so I have been having some problems lately on my 98 GST. Anyway the problems im having seem to be pointing at the ISC but its slightly different than 95% of the post pertaining to it.

First off I have no idle surge at all my RPM will hold rock steady at whatever its current value is.


but my idle seems to be set by temperature the colder it gets the lower my idle will be if its hot out my idle will raise to about 1k-1.1k rpm

also before my car reaches operating temp anytime i give it gas it will stall out as the rpms falls.(pointing to the isc not catching the idle) Also if i try to drive it before my coolant gets to around 175 degrees it will just buck and stall out immediatly as soon as i let out the clutch and apply any load to the motor.

Once the car has reached operating temperature The stallings are gone and the car drives perfectly normal. it catches its idle fine after letting off the throttle.


Only other thing that seems out of place is that my vacuum will sometimes be low when its cold out and therefore the idle is around 620-670 it will only pull 15-16"hg


Boost leaks are out of the question as these problems arrised after doing a boost leak test and fixing a few minor vacuum leaks. It is air tight and hold 25psi for over 2min and slowly leaks down to 14psi that holds indefinatly.(BOV leaks over 15psi)

all my mods are in my profile. I will perform a resistance check on the ISC motor as soon as i get my multimeter back from my friend.

 

[Crazyjoker77]

oh and just another thing if i unplug the ISC My idle shoots up to 1500-1600rpm and holds somewhat steady but still stalls out after the rpms fall while the motor is cold. I have not tried unplugging it with a warm motor.

 

[ZmanIV]

Pull the ISC and ohm out the pins if it is suspect.

go here for new versions if it is bad
http://www.dsmisc.com/dsmweb-dw/index.html

 

[chicagoavenger]

Make sure the motor on the ISC turns with a 9v lantern battery. Just because it ohms out doesn't mean it's always good. Look under ISC testing under the search button and it should be one of the first few threads.

 

[PitBull]

Make sure the motor on the ISC turns with a 9v lantern battery.

Don't you mean a 6v lantern battery? If you use a 9v battery I think you'll burn the motor, I could be wrong though...

 

[chicagoavenger]

Don't you mean a 6v lantern battery? If you use a 9v battery I think you'll burn the motor, I could be wrong though...

You are correct sir thanks it's a 6v for testing. I was incorrect earlier when I said 9.

 

[Crazyjoker77]

okay so i tested my ISC, primary and secondary coil packs, power transistor, and changed plugs and wires. Everything tested okay so now im thinking its either

1- FIAV- not really completly sure how this component works but i am suspecting it as i know it raises idle on cold starts and this issue happened after replacing the TB shaft seals.

2- ISC/biss screw- although my ISC tested good i obviously had to remove the biss screw to replace the o-ring and know its rather tricky to set the base idle on a 2g. Now when i turn my biss screw it affects the idle and seems to stay there instead of trying to self correct itself. also its is almost screwed all the way in to keep the idle below 1000rpms once warm.

3- TPS- tests fine when i use my logger from inside the car 0-99% but when i did the test as per the haynes manual i get a different range than what is called for in the manual but it does range between high and low.


any thoughts/ideas would be welcome

also i would like a little more info on adjusting the Base idle on a 2g dsm and the effects of just using the biss screw. as i beleive this may be my problem.

 

[always_broken]

And to think I sold my ISC for 5 bucks, had no idea they were so much to get.

 

[TsiPat]

I had the same idle problem with my 95 TSi AWD.
It was caused by my O2 sensors.
When the sensors malfunction, the ecu uses the default A/F ratio, hence when the motor warms up it runs too rich and causes the idle to raise a bit. I changed mine recently and now it idles perfectly.
Hope this helps.

 

[romeen]

If your idle is not surging but rather your idle increases in relation to increasing temps it might be that your throttle cable is adjusted too tight. I had a similar problem and this was the cause. Try loosening it a tiny bit and see if that fixes the problem. Refer to this post for an explanation and other good tips. Pay particular attention to the first paragraph.

http://www.dsmtuners.com/forums/tuning-engine-management/241449-tps-reading-idle.html#post151021480

Let me know if this helps. Good luck.

 

[Crazyjoker77]

If your idle is not surging but rather your idle increases in relation to increasing temps it might be that your throttle cable is adjusted too tight. I had a similar problem and this was the cause. Try loosening it a tiny bit and see if that fixes the problem. Refer to this post for an explanation and other good tips. Pay particular attention to the first paragraph.

http://www.dsmtuners.com/forums/tuning-engine-management/241449-tps-reading-idle.html#post151021480

Let me know if this helps. Good luck.

was very informative but was no help. TPS is working correctly and throttle cable is adjusted properly. idle closed switch reads also reads properly.

I'm still thinking it may be MY FIAV as it i only have issues while the car is warming up.

My friends giving me his throttle body to test some things out so im gonna swap over the bottom half of the throttle body and see what happens.

only thing is im not quite sure is the proper procedure for re-installing the TB with a NEW ISC as i know base idle has to be set with a Mitsubishi scan tool for 2G's and not sure if i can use a new ISC without this scan tool. Any input? any1 know the proper procedure?

 

[TsiPat]

Before you do that. Did you checked your O2 sensors like I mention? My problem was very similar to yours, I changed my ISC but it was in fact cause by my O2 sensors. My mech says it something you're suppose to change aroud every 60.000miles but most ppl ignore them.

Let me know if it helps

 

[Crazyjoker77]

Before you do that. Did you checked your O2 sensors like I mention? My problem was very similar to yours, I changed my ISC but it was in fact cause by my O2 sensors. My mech says it something you're suppose to change aroud every 60.000miles but most ppl ignore them.

Let me know if it helps

Im pretty sure my O2 is healthy. My narrowband cycles at idle and cruise conditions, reads rich at throttle and lean when engine breaking. also the voltages check out on my logger.
As well since the problems only arouse after replacing the TB shaft seals im pretty sure it has to do with that.

Also over the past year i have had a P505 code pop(Idle Control system malfunction) up mabey 3-5times upon startup but once cleared doesnt come back for at least a full oil change if that.

so im thinking either my isc or fiav where on there way out and me removing the TB finially sent it past the breaking point.

I did do a resistance check on my ISC and all the coils where withing spec but i did not remove it to inspect it or test it with a 6v battery.

Really i think i got this problem worked out i would just like to know the proper procedure for swaping ISC without messing up my base idle?