What to do when isc is bad.

[lilalex86]

Car was running great put k/n filter on , figured trans was low on fluid and changed filter and fluid week ago. Today started idle surge 1500 rpms up and down crazy, found one vac line leak fixed still messed up. Checked ohms on isc and #6 plug read 42 ohms all others 32, so from what i read its bad. What is best way to fix problem, buy new one from dealer, junk yard or classifieds.Any ideas or advice would be much appreciated.

 

[TURFNNSURF]

Car was running great put k/n filter on , figured trans was low on fluid and changed filter and fluid week ago. Today started idle surge 1500 rpms up and down crazy, found one vac line leak fixed still messed up. Checked ohms on isc and #6 plug read 42 ohms all others 32, so from what i read its bad. What is best way to fix problem, buy new one from dealer, junk yard or classifieds.Any ideas or advice would be much appreciated.

Try a junk yard first, take your OHM meter with you and test the ISC on the junk car first. Chances are the guy at the register won't know what the ISC is and only charge you $5 for it. That is how I got my last ISC.

 

[DevilSperm]

make sure your BISS isnt fuct up before you go spending money on an ISC

 

[lilalex86]

OK Ill try that out sounds better than getting new one. Will any 1g work?

 

[lilalex86]

OK tried a different isc from junk yard and still same problem. What is the one wire on top of throttle body for, makes plunger go in and out. when its disconnected it idles steady.

 

[steve]

OK tried a different isc from junk yard and still same problem. What is the one wire on top of throttle body for, makes plunger go in and out. when its disconnected it idles steady.

It's the Idle Position Switch. It's tells the ECU that the throttle is closed. Disconnecting it fools the ECU into thinking the car isn't idling so the doesn't cut fuel when the idle RPMS are too high which you see as surge but it also means that the ECU can't cut fuel or emulate a dashpot with the ISC when your driving and take you foot off the throttle.
You need to figure out why the engine is idling so high that the ECU goes into surging and fix that.

Steve

 

[lilalex86]

Yeah thats what i thought wasnt sure with chiltons book, try work on it this weekend

 

[DevilSperm]

did you bother adjusting the BISS? or did ya skip that step?

 

[lilalex86]

Yeah tried to adjust BISS but was already bottomed out??????????

 

[DevilSperm]

i think i have mine backed out 1.5 turns or something, its been awhile...i had surge really bad last year and it was just my biss out of whack...my isc is fuct too but when i adjusted the biss the surge went away...most of the time anyway

 

[lilalex86]

Going just great.Have tried 2 ISC motors all same problem with surge. Checked TPS ohms 1100 up to 5000 like book says.Took off throttle body cleaned, replaced coolant hoses, kinked and old, cleaned EGR, checked vac hoses seem good havent replaced yet,will soon, got new BISS and o-ring all back together and no different! Guess Ill check ECU tomorrow and start looking for good mech. I can do basics but this is a trip.

 

[me612]

When you are adjusting your BISS, are you just jumping in there and turning it, or are you grounding the plug in the engine bay before adjusting it? If you just go in there and start adjusting it without the plug grounded, you are going to be sitting there forever trying to get it to work. OR if you are sick of messing with ISC's, just block the thing off entirely with a block off plate.

 

[lilalex86]

Yeah adjusted BISS like vfaq and book says. Tried all three different ISC's again no diffferance. Took apart throttle body blocked off FIAV with jb weld, really thought that was it no.Took out ECM looked good ti is a three year old rebuild, did some ohm test on that and meter went up and down like faq and some ecm web sight said. Have about had it with car now so put it all together looked it over once and radiator leaking top neck totally cracked up. Guess glad I caught it in driveway. Gotta change rad now. Also need to figure on how to double check FCU temp sensor and O2 sensor cause think they are bad from some checks did today gonna research more and order parts. Man its fun sponsering daughters car and working on it. She says needs another car real funny with no money!

 

[me612]

Ya, I to got fedup with idle surge. So I just went ahead and eliminated what I could to prevent it from happeneing. My EGR is gone, along with all the vacuum lines assosiated with it. I also picked up a blockoff plate from one of my local shops. It blocks of the ISC and FIAV. So there's another 2 things that can no longer cause me idle surge problems. If you want one of the plates as well, you can pick em up here.
http://www.qprinc.com/
http://www.qprinc.com/fiav.htm

 

[lilalex86]

Dont know about blocking ISC When I unplug wire to it car idles real high. Wondering where to get other parts like good rad hoses (mits dealer), O2 sensor, Ecu temp sensor. Just ordered new radiator for 105 and didnt have to go out deal with part store, oh thats right they close early on sunday and was more expensive. Thanks for help and links

 

[me612]

It all depends on you man. Blocking off your ISC is simple, but then you will lose it's whole purpose. So when you flip on your AC, your idle will drop, and you won't have an ISC to open up a little to compensate. But if you're willing to deal with that, then just block it off. I only drive my car on the weekends sometimes, so I'm will to deal with it. Different strokes for different folks!! Glad you found a radiator too, I think I posted on your thread on it.

 

[steve]

Blocking off the FIAV and ISC also impact cold starting, deceleration control, and rolling idle speed as well as the ISC managing stopped idle speed and load from the AC compressor and power steering pump. These are all good things from my perspective, so I spent the time tracking down the real bypass air problems and fixing them rather than working around them by hacking up the throttle body.

You can pressure test N/T intakes like we do turbo cars to find the cracked vacuum lines, bad Thermo Valves, leaking EGR gaskets, worn throttle shaft seals, hardened injector insulators, etc that are the cause of too much bypass air leading to idle surge.

Steve

 

[me612]

OK well like I said, different strokes for different folks. I have plenty of friends running fine without an ISC or FIAV. I drive this car on the weekends sometimes. This is not my daily driver. It is my toy that comes out every now and then. I have the time to start it up and let it warm up, so I don't care about the FIAV. I do not use A/C or care if my idle is a little high while rolling, so blocking off the ISC and controlling my idle simply with the BISS works just fine for me. Now if I was driving this thing every day to work in a desert, well then I'd probably keep the ISC because I'd be using the A/C regularly. But I live in Minnesota, so I'm just fine in that arena. I'm sorry you feel my "hacked" method is inferior to yours. I can't compare my car to yours because I don't know you or have ever met you, but I can assure you my car is far from HACKED as you put it. My car is clean, and everything done to it is done by me, with TLC. If I was a HACK, then I would have made my own Block off plate out of an old coffee can and covered it in silicone. But instead I spent the money on a very nice plate made by my local shop.

I'm sorry if I made it sound like the only reason I blocked off the FIAV and ISC is for Idle Surge problems. It had a major roll yes, but I did weigh the ups and downs, and for me, the downs really weren't a big deal so I decided to get the block-off plate for like 40 bux instead of fronting the 80 or so bux for another ISC that will more then likely fail again in a year.

 

[lilalex86]

Status Report: Good that car got idle surge since found out radiator was really messed up!Daughter who drives car would at least been stranded or blown up motor. So put new radiator in with new hoses, tstat, tranny hoses, cap, ectemp sensor,O2 sensor, and vac valve from bone yard.(Broke it putting in temp senor). Was all pretty easy compared to older cars used to work on. Now still have idle surge after car warms up about 2 or 3 minutes. Not as bad as when problem first started. Almost gone when in drive, bad in park or neutral. Gonna try a vac test on motor today if I can borrow gauge from mech at work. Any Ideas!

 

[lilalex86]

Another day. Took off intake snorkle taped and clamp ends put in tub of water checked for bubbles nothing. Put on new clamps for that piece. Did vacuum test was steady 21 looked fine.Blocked of egr valve even though seemed fine no help then unblocked. Changed couple vac hoses messed with some more got pissed been like two weeks messing with this and going to work. Last idea was mess with ISC switch on side one with wire on it. One everthing I read said dont touch. So loosened nut turned the thing idle went down. So a-****ing-mazing dont know exactly how TB is all supposed to be adjusted but this worked. Shut off car turned biss out 2 turns disconnected bat to reset computer then started back up adjusted thing and its 95% fixed. Must have hit it abunch when taken out air cleaner so many times since had car and it loosened up.So probably not right way to do this but until I figure out exactly how its running good again.Any more advice and help is appreciated. THANKS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[lilalex86]

Finally finished, set ips to best of knowledge(need to look at friends manual) set tps, set biss,car is FINE. Think car was not set up right when bought it cause biss was all the way in and ips wire off. A number of other things were wrong with car cause of B.S. mechanics so why should that be right. Plus I think IPS came loose out of adjustment. After fixing everything else that was last problem. Giving car back to daughter until another sponsor job needed!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[zrk666]

OK Ill try that out sounds better than getting new one. Will any 1g work?

no a 1990 isc wont work on any other car but a 89-90.