ANyone ever had an ISC (idle speed control) go bad?
 

Wondering...

Sometimes my idle doesn't catch at the bottom...and stalls.

Sometimes it drops from 1000 (normal idle for me) and goes down to 500rpm and barely catches, stumbles, and picks back up.

Sometimes it only drops down to 800rpm.

PFC has it set for 1000.

Do these things go bad, and if they do.. are these the symptoms?

Car was dyno tuned by Steve Kan - so the timing and everything is good... and it idles fine (a bit rich, but fine) - just doesn't always catch when i come to a stop.

You and I are in the same boat Darren and my car is almost completely stock with 41K on the clock. Have you checked the resistance of the ISC per the FSM to see if it is within specs? You could possibly do it with the ISC on the car (if you're double jointed or have the hands of a 6 year old).

Mine went bad ~ 2 years ago. Car would almost die whenever a/c compressor kicked on.

My hands are cut to holy hell from FD's, but unfortuantely I have ape hands. I might as well get some hair transplants and become a gorilla... my knuckles practically drag on the ground my arms are so long.

Start with cleaning it. Dirty ISC's are FAR more common than bad ones. At the bottom of my UIM writeup I show how to clean it -

http://www.clubrx.org/default.asp?id...ntent=63&mnu=5

I'd also investigate the dashpot - that's a common culprit for stalling when coming to a stop.

Dale

Just take it off the car along with the other uneeded TB stuff (wax rod, coolant, etc), we've written up the details numberous times on the PFC forum.

Typical issue with stalling is the dashpot adjustment, but I've seen dashpots that required replacement when the plunger no longer worked.

the plunger on my dashpot works fine =P it doesn't stick

Ok don't i feel like a damn douche.

The ISC isn't even plugged in....

But when I do plug it in, the car goes to all holy hell. It likes to sit at 1400rpm, and do all sorts of surging, etc.

I remember when Kan tuned it he said it worked, but for some reason couldn't work it into the tune. So I guess he unplugged it and I thought it was plugged in.

Now, what could this possibly be? Do I have to let the PFC re-learn idle? or some shit?
lol

i am now in the same boat Darren... IM me if you can help me

sounds like you should try to get it to relearn?

have the throttle stop screws been played with? if they have this seems to confuse the stock ecu's, dunno about the power fc

i really have the same problem i thought that i had a vacume line loose or a leak so i redid alot of them and it got better but it still idles at 1500 and i cant get it to drop either....... i am new at all of this so do i need to replace the isc or do you think that cleaning them could do them justice?

The ISC only affects the idle when the fans kick in or the AC compressor engages. It is designed to allow more air around the throttle body and, thus, raise the idle temporarily when a new load is placed on the engine. At all other times, the ISC is closed. If your idle problem correlates with the fans coming on or the AC compressor engaging, then it could be the ISC. There is an ohms test described in the FSM as someone else mentioned to check the ISC. Otherwise, your idle settings on the throttle body control your idle, with the dashpot regulating the speed of deceleration. As for what happens when the PFC is tuned without the ISC plugged in, I don't know. It sounds like it is telling the ISC to stay open, thus causing the high idle?? I say that because your idle is acting the same as when the ISC hangs open from debris getting lodged in there.

OK, this is my first post ever, anywhere. But here goes.

JD, seems we share a hometown! Thought it might amuse you hear that Bell Mazda told me I need an "Idle Control Valve" before they can do any diagnostics for me. Now, at this risk of looking foolish if there actually is such, it seems they must rather be referring to the ISC.

Since my symptoms are the same 1400 RPM, I'm definately gonna investigate DaleClark's fix! Because mine will idle correctly on rare occasions, or "search" between the two extremes on others, I think it supports your dirty valve theory.

Dhahlen, you'll undoubtedly have yours fixed long before I do mine and can provide
you any help. I'm just so used to not driving the car, you know?

How sweet would it be to have all the different connects, each with a foot of wire on 'em for FSM tests?

Hey guys I had the same problem...both with the stock ecu and with my powerfc however it got worse with the powerfc. when i had the stock ecu i turned up the base idle and that cured most of it. however with the powerfc it was 10x worse. for those of you with the powerfc check your sensors to see if the clutch sensor is working. My problem was that the input switch for the clutch was bad. Apparently its a common problem on fds. If it shows up as not working on the powerfc (either blinking or not lighting up when you press on the clutch) replacing it should solve your problems. I got my clutch switch from ray crowe at malloy for $16 shipped and it took about 10 minutes to install. Hope that helps.

Let me know if I can help. Always like to keep these 3rd Gens on the road.

Thanks for the offer, jd. Guess I'll PM you if it comes to that.

My ISC came off looking pretty clean, so I'm back to searching for the vac leak? At least I know my ISC is good, and the dealer is suspect (surprise)!

dhalen and sleven, I'm wondering if either of you got yours solved? Thanks for the clutch switch tip, bbade. I'll check it out.

hey man no problem...glad to help a fellow owner. Hopefully you get it fixed up soon because I know how frustrating it is when the car stalls all the time.

I have to say that in my experience, the ISC affects idle at all times, not just while under load. Unplug the ISC on a stock car while the engine is running, no fans, no load...bet the idle drops or changes.

I'd clean the ISC and also clean the throttlebody...focus on the edges of the throttle plates, which get carboned up. They are set at a certain clearance to allow so much air through...and when carbon builds up, that much air cannot get through, so the engine sometimes tends to stall. A lot of newer cars have more precise/sensitive fuel injection, and suffer from this problem much more often. My denali wouldnt idle right when I first bought it until I took it off and soda blasted it clean, now it idles like new.

Sometimes on heavily ported engines I find that it is better to run without an ISC for stability...the computer tends to try to overcorrect in some situations, and it's too hard to get a stable idle with it. In these cases, just unplug it, and bump the throttle stop adjustment screw in some, to raise idle.

Dhalen, you may try bumping the throttle stop screw in a little bit, so the ISC doesnt have to try and work so hard to save the idle. A 900rpm base idle is nothing to be ashamed of if it makes the car more stable.

Hey Guys-

My high idle is SOLVED! Thanks to everyone for their input! Here's what I did:

a) Cleaned and tested ISC per Dale Clark site/write-up. Looked pretty clean.
b) Throttle plates looked okay(?), but hit 'em w/carb cleaner anyway.
c) Did TB coolant bypass (long hose goes to where short hose was), just 'cuz UIM was off.
d) Disabled AWS by removing spring/cranking down far against wax rod. Also made slug from 5/8" bolt for plugging the big hose. Same excuse.
e) Replaced check valves(D Clark) and vac lines(just Goodyear) where reachable.
f) My prior iffy repairs involving superglued DT solenoid nipple was bypassed. Just used rubber vac plugs. It busted again once I got the UIM off. (I'd "fixed" a check valve this way too, that's why I got new ones.)

Stock (except AST) car now idles at 850RPM, dropping a bit with the brakes on (lights?), and rising with the fan or A/C on. Doesn't go over 1000RPM and doesn't super-fast idle (start) or look to stall either. It's 105+ degrees here, though!

Guess there's no telling the cause with certainty, but I can be happy now...at least 'til it fails emissions!