OMG, that is exactly 1 of my 2 main problems on my 1990 miata 1.6. I cleaned each one of those parts that you teplaced, the rough looping idle wasn't fixed. However, a few months before this problem happened, i had removed all the carpet in order to put sound deadening matts & heat shield, to cover all the floor. I noticed my computer (ECM) is located on the passenger inner firewall, just bellow the heater core, at the passengers tip-toes. Thats why the metal shield covers the ecm to protect it & so the passenger doesnt feel that square lump under the carpet. From 1991 or 92, & later models, the ECM is located at the back wall behind the passenger sest, at least 12 inches above the floor in order to protect it from pools of water, ot especially from a clogged heater core that leacks water from condensation from using the AC. I noticed after removing the carpet, that the lower part of the ECM shield was rusted, as well as the holdinf bracket, & the lower one inch of the ECM. Fine, no problem, the idle still worked fine for about a year. But rust being the metal cancer that it is, must have spread on my ECM throughout that year, finally affecting the engine idle like in your miata. What i want to kick myself on the azz for, is that i had gotten the ECM last week from a wrecked Miata in San Bernardino. But since i had racked up already $350 on miata parts, i decidet to forego the ECM. Now im kicking myself on the azz.. And you csnt trust ECM sellers out there on ebay or Offer Up. But i have no choice now. Those clogged up outlets mesnt to allow water to flow out of vehicles, like also on the miata convertible sides, are notoriius for causing rust provlems. Those rusted corners of the rear tire wells is due to gloged outlet holes and rubber lines that extend from the top of the convertible sides, to the lower rear tire well corners.
So glad you made this series man. I've been following the whole thing bc my 94 has a sporadic idle too but my list of things to check only had some of the parts you mentioned so I added the others you went through on this series and will be diagnosing it soon. Much appreciated. I love your channel.
@@creamwobbly that's a good point. 90s Miatas are still pretty sought after nowadays though so I might still fix it up. I'll definitely take that into consideration before I throw a bunch of money at the car though. Thanks for the heads up.
@@genieblack3720 Absolutely. I wasn't able to pinpoint mine to an exact part because I took it to a local JDM shop near me and they couldn't' find anything wrong with the sensors or valves and stuff in the manifold, but another thing that could have been throwing mine off was the tune mapped on my aftermarket ECU, which was installed by a previous owner. The shop redid the tune on it and now the idle sits very stable and the throttle is way more responsive compared to before. I still think maybe there are some parts in the car like the IACV that could probably use some cleaning for better performance but I haven't been able to check on those parts myself without the proper tools. Hope this helps.
@@attentiveoperator I looked at my ECU behind the passenger seat and the bottom of the ECU where all the wires plug in and I could see where it had been water damaged about a half inch above the plug connectors. Some corrosion on the circuit board. I'm going to put a new one in and hopefully that will fix it............
@genieblack3720 oh yeah that's no good. Do you suppose the water damage was from a leak in the soft top? Hopefully changing that ECU out will help. And also hopefully you can find out where the water is coming in so it doesn't get to the ECU again. I regretfully don't have my miata anymore since I had to sell it before moving states. Planning to get another one in the future once I get a garage big enough for all the cars. Good luck with the repair.
This is a great series, been following along because I'm following a high idle when warm. Ithink it's the air choke valve in my case. Maybe episode 7 will be finding how the water got in, and prevent it for next time?
Thanks 🙏 You can clean the IAC with “Sensor Clean” spray. Some folks use throttle body cleaner, which is probably fine too. When you clean the throttle body, the cleaner usually flows in the IAC.
@@MiataMan I got some Miata parts if you might be interested in. Unfortunately I don’t own my Miata anymore after it was stolen from my driveway back in 2019.
Interesting. My 1991 Miata does the same thing with the bouncing idle, but it only does it when its below freezing. When the engine warms up it goes away. I only drive the car in the summer months so the issue only pops up in late spring and late fall so I have not worried too much about it. I do still wonder what causes it which led me to your 6 part series. My miata has no water damage on the floor so Im wondering if its the iac valve.
Well when the IACV was unplugged, it must have removed the bad info it was getting from the damaged ECU. So the engine was able to run at a constant RPM. Most IACV's I've seen that have gone south cause a really high idle, but at the same speed. Good to know that the up and down RPM is indictive of a bad ECU. That car is a shrine of neglect. It was probably left out in the rain with the top down.
That car looks bad from basically every angle you’ve shown us. Engine looks dodgy. It has been repainted which doesn’t matter because the new paint is peeling anyway. And it suffered water damage with probably loads more rust underneath. Respect though, for fixing the issue and teaching us something new.
Mine is doing this. It was running fine and then just started doing this. If you go above 1/4 throttle it just bogs down. If you hold your foot to the floor it does this. What doe you think? th-cam.com/video/16DRemQnHyg/w-d-xo.html
OMG, that is exactly 1 of my 2 main problems on my 1990 miata 1.6. I cleaned each one of those parts that you teplaced, the rough looping idle wasn't fixed. However, a few months before this problem happened, i had removed all the carpet in order to put sound deadening matts & heat shield, to cover all the floor. I noticed my computer (ECM) is located on the passenger inner firewall, just bellow the heater core, at the passengers tip-toes. Thats why the metal shield covers the ecm to protect it & so the passenger doesnt feel that square lump under the carpet. From 1991 or 92, & later models, the ECM is located at the back wall behind the passenger sest, at least 12 inches above the floor in order to protect it from pools of water, ot especially from a clogged heater core that leacks water from condensation from using the AC. I noticed after removing the carpet, that the lower part of the ECM shield was rusted, as well as the holdinf bracket, & the lower one inch of the ECM. Fine, no problem, the idle still worked fine for about a year. But rust being the metal cancer that it is, must have spread on my ECM throughout that year, finally affecting the engine idle like in your miata. What i want to kick myself on the azz for, is that i had gotten the ECM last week from a wrecked Miata in San Bernardino. But since i had racked up already $350 on miata parts, i decidet to forego the ECM. Now im kicking myself on the azz.. And you csnt trust ECM sellers out there on ebay or Offer Up. But i have no choice now. Those clogged up outlets mesnt to allow water to flow out of vehicles, like also on the miata convertible sides, are notoriius for causing rust provlems. Those rusted corners of the rear tire wells is due to gloged outlet holes and rubber lines that extend from the top of the convertible sides, to the lower rear tire well corners.
Amazing work Miata Man. Can’t believe how much water damage it had. Happy to see another NA Miata still running. Love working on these cars.
So glad you made this series man. I've been following the whole thing bc my 94 has a sporadic idle too but my list of things to check only had some of the parts you mentioned so I added the others you went through on this series and will be diagnosing it soon. Much appreciated. I love your channel.
@@creamwobbly that's a good point. 90s Miatas are still pretty sought after nowadays though so I might still fix it up. I'll definitely take that into consideration before I throw a bunch of money at the car though. Thanks for the heads up.
I have a 94 doing this about every other time I drive it. Please let me know if you figure it out.
@@genieblack3720 Absolutely. I wasn't able to pinpoint mine to an exact part because I took it to a local JDM shop near me and they couldn't' find anything wrong with the sensors or valves and stuff in the manifold, but another thing that could have been throwing mine off was the tune mapped on my aftermarket ECU, which was installed by a previous owner. The shop redid the tune on it and now the idle sits very stable and the throttle is way more responsive compared to before. I still think maybe there are some parts in the car like the IACV that could probably use some cleaning for better performance but I haven't been able to check on those parts myself without the proper tools. Hope this helps.
@@attentiveoperator I looked at my ECU behind the passenger seat and the bottom of the ECU where all the wires plug in and I could see where it had been water damaged about a half inch above the plug connectors. Some corrosion on the circuit board. I'm going to put a new one in and hopefully that will fix it............
@genieblack3720 oh yeah that's no good. Do you suppose the water damage was from a leak in the soft top? Hopefully changing that ECU out will help. And also hopefully you can find out where the water is coming in so it doesn't get to the ECU again. I regretfully don't have my miata anymore since I had to sell it before moving states. Planning to get another one in the future once I get a garage big enough for all the cars. Good luck with the repair.
Thank you for the education!
This is a great series, been following along because I'm following a high idle when warm. Ithink it's the air choke valve in my case. Maybe episode 7 will be finding how the water got in, and prevent it for next time?
Well done Miata Man, persistence pays in the end. 👍
Nice job, but YIKES! That car makes me wish I could give it some TLC. It runs too nice to be allowed to rot away like that.
Congratulations, I am glad you got it sorted, a friend has a similar issue, I will check through and see what his issue is👍🇬🇧
Fingers crossed!
all the thumps up in the world to you! by the way, is there a way to clean the iacv?
Thanks 🙏
You can clean the IAC with “Sensor Clean” spray. Some folks use throttle body cleaner, which is probably fine too. When you clean the throttle body, the cleaner usually flows in the IAC.
Hello,
I remember you fixing my red 1990 Miata’s broken passenger side window.
Thank you once again.
Anytime 😊👍 Great to hear from you.
@@MiataMan
I got some Miata parts if you might be interested in.
Unfortunately I don’t own my Miata anymore after it was stolen from my driveway back in 2019.
It's amazing it even started!!!
It's a testament to how resilient Miatas are 👍😎
Interesting. My 1991 Miata does the same thing with the bouncing idle, but it only does it when its below freezing. When the engine warms up it goes away. I only drive the car in the summer months so the issue only pops up in late spring and late fall so I have not worried too much about it. I do still wonder what causes it which led me to your 6 part series. My miata has no water damage on the floor so Im wondering if its the iac valve.
The IAC is likely the culprit in your case. Try cleaning it and see if that helps.
@@MiataMan thank you
If your AC drain stops up, this is where the condensation will drain.
HOWdy M-M,
Thanks
COOP
...
Well when the IACV was unplugged, it must have removed the bad info it was getting from the damaged ECU. So the engine was able to run at a constant RPM. Most IACV's I've seen that have gone south cause a really high idle, but at the same speed. Good to know that the up and down RPM is indictive of a bad ECU. That car is a shrine of neglect. It was probably left out in the rain with the top down.
lol, i will remember this "Shrine of Neglect"
Cool...my 91 is having idle problems and we've done ever thing but check the computer....
Great Job!!
Yayyy!
That car looks bad from basically every angle you’ve shown us. Engine looks dodgy. It has been repainted which doesn’t matter because the new paint is peeling anyway. And it suffered water damage with probably loads more rust underneath. Respect though, for fixing the issue and teaching us something new.
@@creamwobbly So do I, make no mistake. It just seems that this one is *very* far gone.
Oh wow. What caused you to check the ECU,?
*pops the prosecco*
Luckily savage parts are not that expensive. Otherwise it looked like throwing parts on a money pit. This specimen could use some tlc though!
Need a gas tank for a 1991 Mazda miata
Theyre nice when you can find them
Need the gas tank for a 1991 Mazda mazda
No muffler?
It has one, but it’s really loud.
Mine is doing this. It was running fine and then just started doing this. If you go above 1/4 throttle it just bogs down. If you hold your foot to the floor it does this. What doe you think?
th-cam.com/video/16DRemQnHyg/w-d-xo.html
Could be the MAF.
@@MiataMan I changed it already. Waiting on the crank angle sensor now. If this isn’t it I am clueless.
New crank angle sensor does the same thing. What now?