Idle issues
Thread Starter
6th Gear
Joined: Mar 2020
Posts: 6
Likes: 3
Idle issues
Hi, i,m having major issues with idle on the crossfire engine, i,ve worked out if I block both intakes for the iac the engine idles perfectly. How do you know if the iac,s are working, an are they fuse protected? What should I be doing, any help greatly appreciated
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
Hi, i,m having major issues with idle on the crossfire engine, i,ve worked out if I block both intakes for the iac the engine idles perfectly. How do you know if the iac,s are working, an are they fuse protected? What should I be doing, any help greatly appreciated
Alternatively you can plug in a scanner and watch the IAC counts changing. The old Tech 1 scanner works on these cars so does WinALDL on a PC.
Lastly the IACs are not fused they are connected directly to the ECM
Hope this helps
Thread Starter
6th Gear
Joined: Mar 2020
Posts: 6
Likes: 3
Cheers
Thanks for that info. I will check it out in the morning. Both passages blocked put the idle down to 500 rpm. Would you know the best reset procedure for the iac,s please. Would i be right in saying if the ping lee don,t move, more than likely it would be the ecm .? Tia mate
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
Thanks for that info. I will check it out in the morning. Both passages blocked put the idle down to 500 rpm. Would you know the best reset procedure for the iac,s please. Would i be right in saying if the ping lee don,t move, more than likely it would be the ecm .? Tia mate
If you don’t have one get a proper GM Factory Service Manual (FSM) Don’t get a Hayes manual or any of the other after market manual as they don’t have the level diagnostic information. Also with the 84 there is a separate supplement called the Electrical Troubkeshooting Shop Manual, I would recommend that you get it as well.
I don’t think there will be anything wrong with the ECM and there are a lot of things to check first.
What exactly is wrong with your idle?
Last edited by GregMartin; Apr 2, 2020 at 08:39 AM.
Le Mans Master
Joined: Aug 2017
Posts: 6,928
Likes: 1,486
From: New Jersey
If the pintle doesn't move I would lean more towards an iac problem. If it drops to 500 that is reasonable. For an IAC reset I used to disconnect the batter for 15 minutes then do the 40 mph thing. It won't do the learning unless you're above a coolant threshold too. If you're getting 500 with the iac plugged I would say you don't have a vacuum leak. 
My guess is it is idling high? It may not hurt to double check the tps voltage as well. If its a bit high it can sometimes do weird things too.
If you can call @GregMartin thats a safe bet. He can walk you through it.
My guess is it is idling high? It may not hurt to double check the tps voltage as well. If its a bit high it can sometimes do weird things too.
If you can call @GregMartin thats a safe bet. He can walk you through it.
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
If the pintle doesn't move I would lean more towards an iac problem. If it drops to 500 that is reasonable. For an IAC reset I used to disconnect the batter for 15 minutes then do the 40 mph thing. It won't do the learning unless you're above a coolant threshold too. If you're getting 500 with the iac plugged I would say you don't have a vacuum leak.
My guess is it is idling high? It may not hurt to double check the tps voltage as well. If its a bit high it can sometimes do weird things too.
If you can call @GregMartin thats a safe bet. He can walk you through it.
My guess is it is idling high? It may not hurt to double check the tps voltage as well. If its a bit high it can sometimes do weird things too.
If you can call @GregMartin thats a safe bet. He can walk you through it.
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Safety Car
Joined: Nov 2005
Posts: 3,533
Likes: 1,185
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
Tell me he is in the same city as well? Well, if he is, he is one lucky guy for sure. Two of the best guys there on the 84 CF, Greg and Ben. What else could you ask for and Ben has his own chassis dyno. Nice! 1984c4corvette, you are in good hands. 
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
Oh SNAP! Another Aussy with an 84. Tell me he is in the same city as well? Well, if he is, he is one lucky guy for sure. Two of the best guys there on the 84 CF, Greg and Ben. What else could you ask for and Ben has his own chassis dyno. Nice! 1984c4corvette, you are in good hands.
Tell me he is in the same city as well? Well, if he is, he is one lucky guy for sure. Two of the best guys there on the 84 CF, Greg and Ben. What else could you ask for and Ben has his own chassis dyno. Nice! 1984c4corvette, you are in good hands.
Thread Starter
6th Gear
Joined: Mar 2020
Posts: 6
Likes: 3
Thanks
Hi all, thanks so much for everyone,s input, i have taken your advice an sent Greg a message. Hope to hear from him soon. I will post the fix on here just incase anyone else has the same problem down the track. Looks like I,ve found part of the problem, both Iac,s are broken again. First set i put in was told to adjust them to 27mm or somerhing like that, they broke. The second set i put in was told to just put straight in from new an let the ecm do the adjust. Now there broken as well. You can feel the step motor working but the pintle isn,t moving. Hopefully greg can sort. Cheers
Pro
Joined: Mar 2020
Posts: 500
Likes: 27
Recently fixed high idle in a 86. Seemed to definitely IAC related. Only one on this model. I could block the passages as you suggested and idle would drop to about normal. At the time I had no access to a scanner to see data. No codes thrown yet either. As suggested check TPS. Finally a TPS code was thrown ( after praying for help). Checked tps and found to be out of spec. Changed it and idle back to normal. Set tps voltage at idle, min idle. IAC reset by ecm.
BTW: I now have obd1 cable adapter for Snap-On scanner and can see data now.
BTW: I now have obd1 cable adapter for Snap-On scanner and can see data now.
Last edited by Theman5; Apr 2, 2020 at 11:57 PM.
Safety Car
Joined: Nov 2005
Posts: 3,533
Likes: 1,185
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
Hi all, thanks so much for everyone,s input, i have taken your advice an sent Greg a message. Hope to hear from him soon. I will post the fix on here just incase anyone else has the same problem down the track. Looks like I,ve found part of the problem, both Iac,s are broken again. First set i put in was told to adjust them to 27mm or somerhing like that, they broke. The second set i put in was told to just put straight in from new an let the ecm do the adjust. Now there broken as well. You can feel the step motor working but the pintle isn,t moving. Hopefully greg can sort. Cheers
Yeah I don’t know what city he is in, hopefully he contacts me today. He will be lucky if he is in Brisbane because a know a couple of good Corvette guys here. I hope he’s not in Sydney for two reasons 1) the Corona is at its worst there and 2) i recently heard of a guy who was charged $1600 to have both IACs replaced.
Last edited by Buccaneer; Apr 3, 2020 at 02:19 PM.
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
Something VERY odd going on with that. Are you sure you are buying the correct IAC's? No adjustment needed. I just got off the phone with a shop working on an 82 with that issue right now, but the ECM that I suggested to fix the other two issues did indeed fix the CTS and TPS issue, but now has an IAC issue to boot. If both IAC's are NOT moving unless both IAC's are completely dead ie..coils A/B are shorted or open, the issue is either the harness is open or shorted or the ECM is bad. The IAC's are piggy backed together on the same circuit. If the passenger side part of the harness going back to the ECM is bad, the other harness will be bad as well. The 84 FSM is a good manual for troubleshooting this issue. Good luck and use the 84 manual.
Say wha? $1600 for two IAC's? That is flat out robbery. I sure hope you can help this guy out down there.
Say wha? $1600 for two IAC's? That is flat out robbery. I sure hope you can help this guy out down there.
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
I spent a fare bit of time on the phone with him yesterday. Unfortunately he had actually done most of the things I suggested. We are just trying to confirm that he has the right IACs and that they are adjust to 28mm. If I short A and B on my ALDL connector I can see the pintles move in the Idle air passage, they stick out about a 1mm iirc. I’ll try and get a photo of that for him today, provided that my ALDL connector works the same way since I installed the EBL Flash ECM (I’ve never tried it).
I could send him my old ECM but it’s out of a manual car. I also suggested to him to check the harness with some test lights.
Apparently it idles fine until it goes into closed loop then it idles at 1200rpm. That doesn’t sound like IACs to me. It sounds like the ECM is commanding that rpm. But here’s the thing he has replaced all the other sensors that could cause that kind of behavior. So maybe it is the ECM but I think we should step though all the diagnostics first.
I could send him my old ECM but it’s out of a manual car. I also suggested to him to check the harness with some test lights.
Apparently it idles fine until it goes into closed loop then it idles at 1200rpm. That doesn’t sound like IACs to me. It sounds like the ECM is commanding that rpm. But here’s the thing he has replaced all the other sensors that could cause that kind of behavior. So maybe it is the ECM but I think we should step though all the diagnostics first.
Last edited by GregMartin; Apr 3, 2020 at 07:37 PM.
Pro
Joined: Mar 2020
Posts: 500
Likes: 27
IAC and TPS adjustment:
http://garage.grumpysperformance.com...s-and-iac.168/
https://www.thirdgen.org/tpimod2/
http://garage.grumpysperformance.com...s-and-iac.168/
https://www.thirdgen.org/tpimod2/
Last edited by Theman5; Apr 3, 2020 at 07:41 PM.
Pro
Joined: Mar 2020
Posts: 500
Likes: 27
I spent a fare bit of time on the phone with him yesterday. Unfortunately he had actually done most of the things I suggested. We are just trying to confirm that he has the right IACs and that they are adjust to 28mm. If I short A and B on my ALDL connector I can see the pintles move in the Idle air passage, they stick out about a 1mm iirc. I’ll try and get a photo of that for him today, provided that my ALDL connector works the same way since I installed the EBL Flash ECM (I’ve never tried it).
I could send him my old ECM but it’s out of a manual car. I also suggested to him to check the harness with some test lights.
Apparently it idles fine until it goes into closed loop then it idles at 1200rpm. That doesn’t sound like IACs to me. It sounds like the ECM is commanding that rpm. But here’s the thing he has replaced all the other sensors that could cause that kind of behavior. So maybe it is the ECM but I think we should step though all the diagnostics first.
I could send him my old ECM but it’s out of a manual car. I also suggested to him to check the harness with some test lights.
Apparently it idles fine until it goes into closed loop then it idles at 1200rpm. That doesn’t sound like IACs to me. It sounds like the ECM is commanding that rpm. But here’s the thing he has replaced all the other sensors that could cause that kind of behavior. So maybe it is the ECM but I think we should step though all the diagnostics first.
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
Yeah he says he has replaced the TPS and adjusted it (I’ll confirm that again today). He has also replaced the CTS which is another culprit. He has WinALDL which will help if it works.
Le Mans Master
Joined: Aug 2017
Posts: 6,928
Likes: 1,486
From: New Jersey
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019