High Idle.....im Stumped

[supergst]

I have a 1998 GS-T. It just has a evo3 16g on it and no tune or anything. I start the vehicle and it idles fine at 900 RPM, Then as it warms up the idle begins to raise and it tapers off at about 1500-1700 RPM. I have made sure my IAC was good, I have cleaned the throttle body, I have adjusted my throttle cable, And I have also messed with the BISS screw. What else could this be???? I am extremely stumped and starting to get annoyed, please help.

Thanks, Jason

 

[Lofty]

Define messed with cable.
You sure it's not too tight?

Have you checked for Vacuum leaks?
You SURE your isc is good? It could be sticking.
Messed with BISS screw? Or properly adjusted it?


If all else fails, it's probably your FIAV unfortunately.

 

[supergst]

Define messed with cable.
You sure it's not too tight? - Positive.

Have you checked for Vacuum leaks? - Yes.
You SURE your isc is good? It could be sticking. - Yeah, took it out and tested the motor, it twitched when I hooked it up, so I assume it's good.
Messed with BISS screw? Or properly adjusted it? - The BISS screw is all the way down otherwise it will idle over 2,300 RPMs.

If all else fails, it's probably your FIAV unfortunately. - How would I test this?

Thanks for the quick response, I appreciate it.

 

[turbotemper]

There may be a leak in the TB shaft seals. I am having a similar issue but im sure mine is due to a leak in the SMIC. I need to make a leak tester to test each section, but im sure i need to replace the seals or look into the FIAV as the culprit. Ahh its always something isnt it? Gotta love the DSM.

 

[supergst]

There may be a leak in the TB shaft seals. I am having a similar issue but im sure mine is due to a leak in the SMIC. I need to make a leak tester to test each section, but im sure i need to replace the seals or look into the FIAV as the culprit. Ahh its always something isnt it? Gotta love the DSM.

Yeah, I definitely need to do some leak tests. It could be the FIAV, but I'm not sure how to test it. It's always something, for sure.

Haha.

 

[slade4g63]

dsms tend to idle high when u mod them all the time
mine idled because it was never tuned when i did my engine swap and if it stalls when ## driving and u dont reguilate rpm it may be a vacum leak do u have an aftermarket BOV if so is it recirculated if not it will idle high as hell and drop when it wants
also its a good idea to get it tuned

 

[Dsmj89]

Do a boost leak test. Also remember our biss screws are 10+ years old, i would shell out the $20 and purchase the whole biss screw kit.
Also it has happened to me a few times, have you checked to see if your fuel pressure solenoid line that runs from the solenoid to the fpr or intake manifold has come off ?

 

[Lofty]

If the ISC only just twitched, it still doesn't rule it out as being Okay.

Check the resistance between the pins and get back to us.

 

[supergst]

If the ISC only just twitched, it still doesn't rule it out as being Okay.

Check the resistance between the pins and get back to us.

They were tested to 29.5 Ohms.

I read anywhere from 28-33 Ohms is normal.

 

[supergst]

dsms tend to idle high when u mod them all the time
mine idled because it was never tuned when i did my engine swap and if it stalls when ## driving and u dont reguilate rpm it may be a vacum leak do u have an aftermarket BOV if so is it recirculated if not it will idle high as hell and drop when it wants
also its a good idea to get it tuned

Nope, no aftermarket BOV. Yeah, but it's been running with no tune for a long time and this just started not too long ago.

Do a boost leak test. Also remember our biss screws are 10+ years old, i would shell out the $20 and purchase the whole biss screw kit.
Also it has happened to me a few times, have you checked to see if your fuel pressure solenoid line that runs from the solenoid to the fpr or intake manifold has come off ?

Thanks, I'll check out that BISS screw kit!

I haven't checked specifically to see if that line is off, but I'm sure it's not. I'll check again anyway, though.

Thanks!

 

[rush2252]

SAS screw or BISS screw should be screwed all the way in and then out 1/4 turn to factory specs. Check the obvious sounds like you have a major vacuum leak. You can get a flammable liquid such as car cleaner and spray it around the intake TB etc if it idles up and the liquid sucks into the gasket or flange you have a vacuum leak. Check the TB this is usually the first place to check. Its probably not a boost leak or it would run like shat if its a large one. I would say def vacuum line Check to see if the PCV valve rattles when you shake it.

 

[supergst]

SAS screw or BISS screw should be screwed all the way in and then out 1/4 turn to factory specs. Check the obvious sounds like you have a major vacuum leak. You can get a flammable liquid such as car cleaner and spray it around the intake TB etc if it idles up and the liquid sucks into the gasket or flange you have a vacuum leak. Check the TB this is usually the first place to check. Its probably not a boost leak or it would run like shat if its a large one. I would say def vacuum line Check to see if the PCV valve rattles when you shake it.

If the BISS screw is anything but all the way down, it just idles higher. I mean like 2,500 RPM. Already checked for obvious leaks, sprayed TB cleaner around, no luck. I'll check the PCV for sure.

Thanks for the insight.

 

[Lofty]

Is your closed idle switch causing the throttle plate to let in more air?

 

[dsmfa9nutter]

Listen to lofty, he knows all about what he's talking about.

It's either a mechanical issue or a software issue. Unplug your isc and crank your biss in all the way. It should die, if it doesn't, you have a vacuum leak or your throttle plate isn't closing all the way.

 

[pandabeartsi]

this could also be bad maf settings.. this happened with my car and after i got a new maf it went away

 

[supergst]

Listen to lofty, he knows all about what he's talking about.

It's either a mechanical issue or a software issue. Unplug your isc and crank your biss in all the way. It should die, if it doesn't, you have a vacuum leak or your throttle plate isn't closing all the way.

I'll definitely have to try that, thanks! That will definitely help me narrow it down.

this could also be bad maf settings.. this happened with my car and after i got a new maf it went away

I will look into this too, thank you.

 

[Lofty]

Listen to lofty, he knows all about what he's talking about.

It's either a mechanical issue or a software issue. Unplug your isc and crank your biss in all the way. It should die, if it doesn't, you have a vacuum leak or your throttle plate isn't closing all the way.

Ahahah, you cheeky bastard

Mecha ain't too bad either.



Give it time, you'll figure it out eventually.
You can pm me if you have any extra questions, I know ALL about this junk.

 

[Kokomoguy30]

Im having a similar problem Thanks for all the ideas. When you pull the BISS screw the oring is probably going to be shot you can just replace it with a quality o-ring for a buck. The throtlle shaft seals are another good bet, I had to replace mine and if you do you have 2 options. You can either find the seals or you can use o-rings in the original seal housings. Just Google dsm throttle shaft seal replacement and you will find all the info you need to do it. I have done it but I dont have the links now.