86 idle problems

[Ryan S]

I know there’s been many posts about 86 idle issues, but none seem to answer my questions.

It all started when I took off my TB to put some fresh gaskets in it and to overall clean it. During that process I never touched the TPS, but I did take out the ISC to have a look at it and found the screws to be burnt? Like there purplish blueish. Put it back in as it ran good before I pulled anything. During that process I soldered in new injector clips, and I’m 99% sure I soldered the correct wires together and had no cold solder joints. 
 

after re-installing everything, new vac lines all ran correctly (I’ve checked numerous times), TB installed correctly, my car will not idle at all. I have to have my foot on the pedal and manually idle it. Revs out pretty good but won’t idle. Now I thought why not buy new injectors as these look pretty bad. I bought Southbay 850cc injectors, installed them and it struggles to idle. Even worse than it did before. It’ll kinda rev out fine but will not idle. 
 

I have an adjustable FPR as I read that for aftermarket injectors you need higher pressure. Put that in with a gauge, which reads 42psi which should be plenty and it still runs like poop. It smells super rich when you try to get it to idle. Even with factory injectors back in. 

I can’t really do a TPS/ISC reset as I can’t even get it to idle. Maybe someone knows of a cheat that you can do to rule some things out??

any help would be appreciated! I just wanna enjoy some backroads with this car.

thank you!

[psu_Crash]

42psi is too high for the factory injectors. Sounds like you already know that though. Are you setting the FPR without a vacuum connected? Otherwise it will be too high. I don't remember if it will prime the pump when you turn on the key. Mine has been far from stock for a LONG time. That's one way to see pressure without starting the car if it will. Might require 2 people since even though pressure shouldn't bleed off quickly it will still drop. 

[Ryan S]

On 7/7/2025 at 6:43 PM, psu_Crash said:

42psi is too high for the factory injectors. Sounds like you already know that though. Are you setting the FPR without a vacuum connected? Otherwise it will be too high. I don't remember if it will prime the pump when you turn on the key. Mine has been far from stock for a LONG time. That's one way to see pressure without starting the car if it will. Might require 2 people since even though pressure shouldn't bleed off quickly it will still drop. 

I do know that 42 is high for stock injectors, i haven’t ran it yet with the old injectors back in. When I put the adjustable FPR it came set at 42psi, which I thought was perfect for aftermarket injectors so i didn’t mess with it. 
 

When I do put back in the old injectors to see if it’ll even run better, I’ll have to adjust it of course. Also isn’t stock pressure like around 38psi? Just want to make sure as when I do go to adjust it I do it right.

It’ll only prime the pump when ECU sees rpm’s, so I’d need to crank it which isn’t a big deal.

I have unplugged the ISC, MAF, IAT, to see if it’ll run better and none seem to improve my symptoms.

thanks for your reply, any help is appreciated!

[psu_Crash]

Gotcha, I couldn't remember if the stock system primed or not. Yes, I believe 38psi is correct for the stock injectors. Southbay advertises their injectors as a "direct fit, compatible with the stock ECU" I wonder if that means they are designed to work at the lower pressure? Easy enough to try.

On my 86 unplugging the MAF actually made it idle better, so I left it that way for years. 86 are a breed of their own. The IAT being unplugged should have caused a rich condition, but if you are already rich... 

Is the ground to the intake manifold still there and in good shape? I've seen grounding cause all sorts of weird issues. Probably not the likely culprit in your case, just something I thought about since a lot of sensors use that for a ground reference. 

You mentioned it smells rich. Have you pulled a plug to verify? Or noticed black smoke when you stab the throttle?

[Ryan S]

3 hours ago, psu_Crash said:

Gotcha, I couldn't remember if the stock system primed or not. Yes, I believe 38psi is correct for the stock injectors. Southbay advertises their injectors as a "direct fit, compatible with the stock ECU" I wonder if that means they are designed to work at the lower pressure? Easy enough to try.

On my 86 unplugging the MAF actually made it idle better, so I left it that way for years. 86 are a breed of their own. The IAT being unplugged should have caused a rich condition, but if you are already rich... 

Is the ground to the intake manifold still there and in good shape? I've seen grounding cause all sorts of weird issues. Probably not the likely culprit in your case, just something I thought about since a lot of sensors use that for a ground reference. 

You mentioned it smells rich. Have you pulled a plug to verify? Or noticed black smoke when you stab the throttle?

I did have a stock psi FPR installed before, which it didn’t run and why I bought a adjustable one to see if the more fuel pressure would help but it didn’t…

Yeah when I unplugged my MAF it ran really bad, and that’s when it was actually running good. I wonder if maybe mines bad and that’s why unplugging it doesn’t help cause I know a lot of people say they can be ran without. Maybe even my IAT is bad?

when I had the TB apart I cleaned the contacts on that ground, maybe I installed that wrong, who knows it was probably late when I got it back together. Lol. 

I haven’t pulled plugs yet, but it’ll burn your eyes if you’re around it and there’s a little bit of black soot in the exhaust pipe, but doesn’t blow any black smoke when I get it to rev out good. I do know these cars are supposed to run rich so maybe its alright. I guess I don’t remember what it was like when it ran good.

also just a wonder, I bought a MSD blaster ll when I was in the restoring phase and the first start of the car was good and I never checked the resistances. But I just checked them and the secondary resistance is a bit lower than what FSM shows. Could that be an issue? I wish I would’ve checked it before to see if the coil had gone bad. Also not a hard issue, just have to get a good coil.

thanks for your help!

[psu_Crash]

That definitely sounds rich, I would expect a little puff of black though. Especially at idle they do like to be a bit rich. As for the MAF, it seems to be hit or miss on an 86. Some are fine without it, others not. 

You can test the IAT. I believe the specs are in the service manual or they are definitely buried here somewhere. Same for the blaster coil. I'm sure you can find primary and secondary specs from MSD. In my experience if the coil is bad it wouldn't rev well, especially under load. My money is on something around the TB. 99% of the time the problem stems from where you worked on it last. Usually late night and not 100% sober has caused me some grief once or twice 😄 If you cleaned the ground and reinstalled then I can't imagine that is the issue. You can always take a resistance reading from the ground connection to the top hat on the TB just to be sure there is a good connection. Also from that connection to another spot on the body just to make sure you have a solid ground. Might be a stretch, at least you can be sure then. 

[Ryan S]

5 hours ago, psu_Crash said:

That definitely sounds rich, I would expect a little puff of black though. Especially at idle they do like to be a bit rich. As for the MAF, it seems to be hit or miss on an 86. Some are fine without it, others not. 

You can test the IAT. I believe the specs are in the service manual or they are definitely buried here somewhere. Same for the blaster coil. I'm sure you can find primary and secondary specs from MSD. In my experience if the coil is bad it wouldn't rev well, especially under load. My money is on something around the TB. 99% of the time the problem stems from where you worked on it last. Usually late night and not 100% sober has caused me some grief once or twice 😄 If you cleaned the ground and reinstalled then I can't imagine that is the issue. You can always take a resistance reading from the ground connection to the top hat on the TB just to be sure there is a good connection. Also from that connection to another spot on the body just to make sure you have a solid ground. Might be a stretch, at least you can be sure then. 

Yeah, I guess I don’t know if it blows any when I was actually able to drive it. 
 

I’ve tested the IAT, MAF and they test a bit over, but nothing too abnormal. The ISC is something that I tested and the number was abnormally high, but the car used to idle so I just put it back in. As for the coil on summit it shows the resistances and they are quite a bit off from what mine are, which is weird?? It’s basically brand new.

i know it’s definitely something to do with the TB but I’ve checked over it so many times that I lost count and i couldn’t see anything out of the ordinary. I think it’s something to do with an electronic like the ISC or something. I wish I was able to get the car to somewhat idle so I can do a TPS/ISC reset.

thanks for your response!

[psu_Crash]

I'm not really sure what to tell you. It "shouldn't" have anything to do with the ISC though. Possibly triple check the voltage and connections at the injector clips. Although I would think that would cause a lean condition there if that was the problem. They generally aren't polarity sensitive either. It just affects opening time IIRC. 

Strange that the coil doesn't test in spec. What did it measure compared to what it should be? Can you take a video of the car running/attempting to run? I'm curious. Happen to pull the plugs yet and see if they all look sooty?

If you were closer I'd come over and go through it with you! A second set of eyes is sometimes all you need, or then at least someone can share in the confusion. Maybe someone local with knowledge of these can help out?

Edited July 13, 2025 by psu_Crash

[LizardKing]

Did you cut and solder one wire at a time on the injector clips?  Put everything back to stock as it was before you took it apart and start from there. 

 

I can't remember if it's the same as the 87 but you need to reset the isc with the car not running. The isc needs to relearn the idle position. I've done it to my 87 but that was a long time ago. 

Edited July 16, 2025 by LizardKing

[scott87star]

Injectors don’t care which way they are wired, it is best practice to do it the same for troubleshooting.  It sounds to me like you’ve got debris in the pintle of one or both, happened to me years ago with my 87.  I had to remove both injectors and flush them backwards to finally fix it after several failed test drives.

[Ryan S]

On 7/12/2025 at 7:23 PM, psu_Crash said:

I'm not really sure what to tell you. It "shouldn't" have anything to do with the ISC though. Possibly triple check the voltage and connections at the injector clips. Although I would think that would cause a lean condition there if that was the problem. They generally aren't polarity sensitive either. It just affects opening time IIRC. 

Strange that the coil doesn't test in spec. What did it measure compared to what it should be? Can you take a video of the car running/attempting to run? I'm curious. Happen to pull the plugs yet and see if they all look sooty?

If you were closer I'd come over and go through it with you! A second set of eyes is sometimes all you need, or then at least someone can share in the confusion. Maybe someone local with knowledge of these can help out?

Yeah I’m not sure either😆 I’ll have to check connections and put a noid light on the clips and see if they are opening properly.

the primary resistance was exactly where it was supposed to be, the secondary resistance was about 2k ohms lower from what FSM says it should be. I bought a new coil to see if it makes any difference. Can’t really see the coil being my culprit, but it does act as if it’s misfiring bad. I’m probably going to put my old injectors back in as it did run much better than the aftermarket ones, maybe mine are faulty. Then I could take a video of it running, with the new injectors in it’s hard to take a video because it’s hard to keep the car running, it stumbles pretty bad. I haven’t pulled plugs yet, but will eventually do it to see.

Thanks for your help!

[Ryan S]

23 hours ago, LizardKing said:

Did you cut and solder one wire at a time on the injector clips?  Put everything back to stock as it was before you took it apart and start from there. 

 

I can't remember if it's the same as the 87 but you need to reset the isc with the car not running. The isc needs to relearn the idle position. I've done it to my 87 but that was a long time ago. 

Yeah I cut one at a time made sure it was positive and negative and soldered em in. 

i haven’t really put anything aftermarket in other than injectors. I’ve put my old ones back in before and it does run a lot better than the aftermarket ones but it still won’t idle without my foot on the pedal. 

I’ll have to look at the FSM but I’m pretty sure you need to have the car somewhat running to be able to do a TPS/ISC reset.

thanks for your reply!

[Ryan S]

18 hours ago, scott87star said:

Injectors don’t care which way they are wired, it is best practice to do it the same for troubleshooting.  It sounds to me like you’ve got debris in the pintle of one or both, happened to me years ago with my 87.  I had to remove both injectors and flush them backwards to finally fix it after several failed test drives.

My old injectors seem to run pretty good, I wonder if the aftermarket injectors I bought are faulty.

thanks for your reply!

[tux]

I’ve had negative luck with aftermarket injectors on my 86.

[Ryan S]

5 hours ago, tux said:

I’ve had negative luck with aftermarket injectors on my 86.

Yeah, I’ve heard that from a couple people now. I bought OEM “refurbished” injectors. Hopefully that helps out some. I know mine had a pretty significant crack in the plastic and were overall pretty bad.

thanks for your input!

[LizardKing]

Have you tested the isc for proper function? I took mine apart to clean out the old grease and apply some model train grease. It wasn't working smoothly and sometimes would pause before reaching the idle position to signal the computer.  It turned out to be a wire in the isc not making good contact.  If I remember correctly, it broke off at the solder joint inside the isc. 

 

Vacuum leak?  Did you change the throttle shaft seals? Maybe damage to the throttle shaft seals during the cleaning if not new.

Edited July 18, 2025 by LizardKing

[Ryan S]

7 hours ago, LizardKing said:

Have you tested the isc for proper function? I took mine apart to clean out the old grease and apply some model train grease. It wasn't working smoothly and sometimes would pause before reaching the idle position to signal the computer.  It turned out to be a wire in the isc not making good contact.  If I remember correctly, it broke off at the solder joint inside the isc. 

 

Vacuum leak?  Did you change the throttle shaft seals? Maybe damage to the throttle shaft seals during the cleaning if not new.

I guess I haven’t properly tested it as I don’t know how. Although when you turn the key on you can hear it make a noise. Doesn’t really sound like a “zip” like everyone says, but makes a noise. Also I guess I haven’t looked at it while someone turns the key to see if it moves.

 

I couldn’t imagine the throttle seals got damaged in the cleaning, nor did I change them cause there was no shaft play, everything seemed tight and good.
 

thanks for your reply!

[LizardKing]

12 hours ago, Ryan S said:

I guess I haven’t properly tested it as I don’t know how. Although when you turn the key on you can hear it make a noise. Doesn’t really sound like a “zip” like everyone says, but makes a noise. Also I guess I haven’t looked at it while someone turns the key to see if it moves.

 

I couldn’t imagine the throttle seals got damaged in the cleaning, nor did I change them cause there was no shaft play, everything seemed tight and good.
 

thanks for your reply!

The nose switch needs to be pressed in order to send the signal to the computer to idle. Make sure it's extending out till the switch is pressed. 

 

I'm not sure how to test the switch but it should be on here somewhere. Shaft seals get dry and stiff preventing a good seal. They should be changed if they are the originals. 

[Ryan S]

On 7/19/2025 at 5:43 AM, LizardKing said:

The nose switch needs to be pressed in order to send the signal to the computer to idle. Make sure it's extending out till the switch is pressed. 

 

I'm not sure how to test the switch but it should be on here somewhere. Shaft seals get dry and stiff preventing a good seal. They should be changed if they are the originals. 

Sorry for the VERY late response 😅 been pretty busy so I kinda forgot about this. 
 

anyway, I just put in the refurbished injectors and its way better than the aftermarket ones although it wouldn’t idle without my foot on the gas. Turned up the idle screw until it idled by itself and it did just fine. Did a tps/isc reset and it seems to be doing much better. I don’t know how the idle screw changed from me cleaning the TB but ok?? 
 

still has a very faint miss at idle, don’t know what that’s about but it seems to overload itself on fuel cause when you rev it and let it come back to idle, it’ll idle fine until it overloads itself. But now the car runs and drives  I can finally go enjoy some backroads.

thank you all for the help and responses, i greatly appreciate it!