2G Idle Control System Malfunction P0505

[turboTSi1320]

I just got my ECU read and it came up to be PO505 IDLE CONTROL SYSTEM MALFUNCTION. Why would this be happing and what will it take to be fixed?? Would a Vehicle speed sensor fix it? Is it bad tp be driving it with the light on?

 

[19GS-t97]

I actually have the same light on now. It can be a bunch of things. Search under BISS or ISC motor. It really isnt too bad to drive with it on, but i would just try adjusting the biss first maybe the oring on it is shot. If you search the code there should be a hole bunch of posts i remember reading when i was having the problem. Hope this helps man

 

[ddavisaf]

Usually replacing or cleaning the ISC will fix this problem. Sometimes this can be a clogged FIAV (Fast Idle Air Valve) but it's not nearly as common.

 

[dsmpower1]

Are you having any problems with your idle reving up and down when in neutral. If so you may have idlesurge, there is a great website that someone on here talks about, if you search under idle surge, it will probably bring it up.
Right now I need a new idle control motor, I can't find one cheaper that 250$. I have been driving with mine not working properly, it shouldn't really be to bad for the car, but it is a pain in the ass driving around in a parking lot. Good Luck

 

[ddavisaf]

ISC's can be found at www.diamondstarmotorsport.com , www.slowboyracing.com , www.mitsubishigraveyard.com

 

[KoolTrix]

Where is the ISC or FIAC located at?

 

[Bestwestranger]

I know this is an old thread, but I recently had some experience that might shed a little light on the subject...

I had my head rebuild last week, and when it came time to put it all back together, I decided that because I live in Arizona I didn't need the coolant lines that run through the throttle body. Afterwards I spent 2 days trying to track down the idle surge that had apparently come out of nowhere. After spending a great deal of time searching and reading, I found out that the FIAV or FIAC depends on the temperature of the coolant passing through the TB to set the idle. High when the engine is cool, low when its warm or hot. By taking the FIAC out of the loop, it never saw any change in temp and ran like it was cold. Everything else on the car was telling the ECU otherwise, so presto, idle surge. Once I reconnected the TB to the cooling system, the idle surge more or less went away. It still surges for half a minute or so, but always settles down into a nice calm idle.

Where is the FIAC? Well, on a 1G it's built into the TB and cannot be replaced,repaired, or adjusted (to my knowledge) short of replacing the entire TB. I don't have any around to dissect, and they are much too expensive to replace if I happen to screw it up, so I haven't attempted to investigate any further, other than digging around on the net.

What will it hurt? Probably not much, but you will most likely be running rich at idle and possibly everywhere else as well. I noticed my knock count was at 0 under 16 psi of boost, and my EGT's were about 100* higher than normal while cruising on the highway. Because I couldn't maintain a solid, normal idle, I also couldn't set the timing after reassembly and had to play it by ear. Once I got everything back the way it should be I found that my base timing was set about 10* instead of the recomended 5*. No knock and that much timing? It had to be running on the rich side...

Hope this helps!

Update: I just found that you can disconnect the lines as long as you remove the FIAC part of the TB and plug the hole so that it can't let any air through. Time to find a spare TB!

 

[phreak965]

i have a problem w/ idle surge too but a little different (it's so random). sometimes it throws a p0505, most of the time it doesn't. it always runs fine when the engine is cold (800-1200rpm) but when it warms up sometimes it idle surges when the a/c isn't on (when the a/c is on it idles high sometimes, and sometimes it doesn't, but never surges) if i've driven the car for 20mins or so it will be either high-idle or surging though. anyone? :/

 

[voodoogsx]

i have a problem w/ idle surge too but a little different (it's so random). sometimes it throws a p0505, most of the time it doesn't. it always runs fine when the engine is cold (800-1200rpm) but when it warms up sometimes it idle surges when the a/c isn't on (when the a/c is on it idles high sometimes, and sometimes it doesn't, but never surges) if i've driven the car for 20mins or so it will be either high-idle or surging though. anyone? :/

Seeing as I just ran into a similar issue with my idle, I thought I'd add to this one.
My issue was this.
one of the egr vac lines came off, caused the idle to run high(2k region). I connected it and fastened it on with a tie wrap. It ran great, idle was great and everything. Thinking it was stable, I drove it to work. about 15 mins into my drive I'm noticing that when I stop my idle still seems to be pretty high(1200), but slowly goes back to to around 750ish.
Seems like a vac leak to me...just not sure where as the vac lined I fastened was still on nice and tight.
I had checked the other end of the vac line and noticed it was just hanging on...easily could cause a vac leak there....also, ealier in the week, but when I checked that part of the vac line, it broke the seal that was keeping on so now it was loose. Since I'm at work, I don't have any extra tie wraps(used em up)I just ductape it...that actually held till I got home where the vac line came off....but not before I got the p0505 cel code.

I also managed to break the boost gauge vac line as the plastic had been heatcycled enough that when I tried to ben it slightly it broke....I did a quick fix(also with some ductape) but this didn't seem to have a leak around it....I'll be fixing it this weekend as well...

I'll see about updating this post when I resolve the issue, which will hopefully be just fastening the vac line for the egr.