Iac Valve Noise
Thread Starter
Race Director
Joined: Jan 2006
Posts: 10,039
Likes: 0
From: CA
Iac Valve Noise
Hi,I have been fighting a idle miss for some time now,and in the course
of resetting mininum air idle I noticed that when in the diognostic mode,
jumpered aldl,ignition on,my IAC valve chatters.Eg. TIC,TIC,TIC,TIC fast.
Is this normal? Manual does not address this.It is a stock '86.
My gut tells me that this isn't right ,but I don't want to throw more parts at it unnecessarily either.
My major problem is I don't know anybody local with a C4 L98
that I can actually hear run,maybe that's the way they all idle.I do the search thing and I do see alot of complaints about idle.I've cleaned and adjusted the valve to proper depth,but the engine still "hunts" for idle rpm, like it skips a beat. About the only thing I have not done is replace the injectors.Should I just go ahead and replace the valve?
Thanks for your help in advance.
of resetting mininum air idle I noticed that when in the diognostic mode,
jumpered aldl,ignition on,my IAC valve chatters.Eg. TIC,TIC,TIC,TIC fast.
Is this normal? Manual does not address this.It is a stock '86.
My gut tells me that this isn't right ,but I don't want to throw more parts at it unnecessarily either.
My major problem is I don't know anybody local with a C4 L98
that I can actually hear run,maybe that's the way they all idle.I do the search thing and I do see alot of complaints about idle.I've cleaned and adjusted the valve to proper depth,but the engine still "hunts" for idle rpm, like it skips a beat. About the only thing I have not done is replace the injectors.Should I just go ahead and replace the valve?
Thanks for your help in advance.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
When you put the ECM into diagnostic mode the IAC is supposed to close. The ticking your describe sounds like it trying to close further, beyond closed, and is slipping, internally. You might pull it back out and play with it a little.
The idle sounds like the mixture may be lean. Check for vacuum leaks and check out the EGR valve. Have you set the minimum air adjustment?
RACE ON!!!
The idle sounds like the mixture may be lean. Check for vacuum leaks and check out the EGR valve. Have you set the minimum air adjustment?
RACE ON!!!
Pro
Joined: May 2002
Posts: 541
Likes: 2
From: Kalama WA
When I cleaned and reset My 86, it did the same thing-it made alot of noise. I don't believe the noise indicates it being bad. I installed a brand new one in my friends 87- made the same noise in dia. mode.
Thread Starter
Race Director
Joined: Jan 2006
Posts: 10,039
Likes: 0
From: CA
When I got home,I cracked the FSM and found that that the IAC is controled from the ECM by pulses or "counts",but really doesn't say anything about noise.From what I gather I need what is called a IAC driver and node light kit from spent-moore tools to accurately test the IAC.I think it will be cheaper to just replace the valve.
I did find that if the AIC is not getting the signal,it should throw a 35 code,which it is not.
I have done just about every thing,cleaned TB,new plugs,wires,cap rotor,checked EGR function,vaccuum leaks,solenoids,sensors,timing,TPS,idle adjustment as per FSM,compression,fuel pressure , you name it! But it still has a miss at idle,after 700 it smooths right out.I was hoping that the IAC is faulty,but now I have my doubts.I will try cleaning it again one more time.I also read that the A/C relay can cause rough idle if shorted ,I'll check that too.
About the only thing left is injectors,I ran some Chevron cleaner already,but next fill up I'll try some more.
One person said just set the idle at 700 and forget about it,he may be right.Any ideas please let me know,thanks again.
I did find that if the AIC is not getting the signal,it should throw a 35 code,which it is not.
I have done just about every thing,cleaned TB,new plugs,wires,cap rotor,checked EGR function,vaccuum leaks,solenoids,sensors,timing,TPS,idle adjustment as per FSM,compression,fuel pressure , you name it! But it still has a miss at idle,after 700 it smooths right out.I was hoping that the IAC is faulty,but now I have my doubts.I will try cleaning it again one more time.I also read that the A/C relay can cause rough idle if shorted ,I'll check that too.
About the only thing left is injectors,I ran some Chevron cleaner already,but next fill up I'll try some more.
One person said just set the idle at 700 and forget about it,he may be right.Any ideas please let me know,thanks again.
Pro
Joined: May 2002
Posts: 541
Likes: 2
From: Kalama WA
I have four guesses. It's up to you to eliminate each one- by testing with your FSM by your side. 1- tps. 2-iac. 3. maf 4. vacuum leak somewhere. Your FSM has many diagnostic charts that would really help you out.
Thread Starter
Race Director
Joined: Jan 2006
Posts: 10,039
Likes: 0
From: CA
Originally Posted by kize
I have four guesses. It's up to you to eliminate each one- by testing with your FSM by your side. 1- tps. 2-iac. 3. maf 4. vacuum leak somewhere. Your FSM has many diagnostic charts that would really help you out.
factory tools,not a schmuck like me!!
But I'll muddle through it,and in the meantime I'll just drive this sucker!!
Racer
Joined: Jan 2005
Posts: 476
Likes: 0
From: Tucson, AZ. L98-85 AUTO COUPE: 120k MILES: daily driver. SOUND OFF IF YOU'VE BEEN THERE. Ex-Jumpin' Junky-82nd Airborne-2/505 PIR: 1st ID-1/16th Inf: Recon Marine Retread. GOD BLESS GRUNTS.
Originally Posted by GIMMESOME
Thanks Kize,I'm not giving up,the FSM is a great help but it can be a little daunting at times,after all it is written for a pro with the proper
factory tools,not a schmuck like me!!
But I'll muddle through it,and in the meantime I'll just drive this sucker!!
factory tools,not a schmuck like me!!
But I'll muddle through it,and in the meantime I'll just drive this sucker!!
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I have a DUMN idea that was found ,After months of searching and caving into bumping up the idle, on my 87 years ago...When i removed the throttle body and put in a new gasket it tightened my cruise control cable just a very little bit when a muscrat guy looked at it and loosened it just a bit it went back to normal and i was able to bump my idle back down again. He said that it can cause the vacuum to turn on and off when too tight and act like a leak...I still don't beleive that expaination but it doesn't cost you more than a few moments to check, and it did fix mine.
BTW,I have also heard that not using the right one of the 2 TB gasket choices causes some weird things including irattic idle??? hope you kept your old one if you replaced it.
BTW,I have also heard that not using the right one of the 2 TB gasket choices causes some weird things including irattic idle??? hope you kept your old one if you replaced it.
Thread Starter
Race Director
Joined: Jan 2006
Posts: 10,039
Likes: 0
From: CA
Originally Posted by todd_vette87
I have a DUMN idea that was found ,After months of searching and caving into bumping up the idle, on my 87 years ago...When i removed the throttle body and put in a new gasket it tightened my cruise control cable just a very little bit when a muscrat guy looked at it and loosened it just a bit it went back to normal and i was able to bump my idle back down again. He said that it can cause the vacuum to turn on and off when too tight and act like a leak...I still don't beleive that expaination but it doesn't cost you more than a few moments to check, and it did fix mine.
BTW,I have also heard that not using the right one of the 2 TB gasket choices causes some weird things including irattic idle??? hope you kept your old one if you replaced it.
BTW,I have also heard that not using the right one of the 2 TB gasket choices causes some weird things including irattic idle??? hope you kept your old one if you replaced it.
May have been the first time in many years it was even used and it seemed to work great.
But the problem did start sometime after that.This weekend I am going
going to check out the CC mechanism .
Wouldn't that be something if after all I've done,it was that simple.
Well,a guy can hope,I'll keep you posted,thanks.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by GIMMESOME
One person said just set the idle at 700 and forget about it,he may be right.Any ideas please let me know,thanks again.
RACE ON!!!
