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Does your idle fluctuate? Does it go from normal to 1800 RPMS and back to normal again?

Do you have a 90-93?

Your ISC aka ISCV aka idle speed control valve is probably dirty!

It happens with these cars.

The ISC is about $400 new, so cleaning it should be done with care.

HERE'S ALL YOU NEED TO KNOW ABOUT IT!


THIS ONE IS GOOD, TOO, FOR YOU A.D.D. TYPES



Other helpful info:

*the screws that attach the ISC to the throttlebody are SOFT, which means they are easy to round out the heads. Try clamping a pair of vice grips on the sides of each screw head and turning it WHILE using a phillips screwdriver.

* there are two gaskets you might have to replace when doing this job; the throttlebody gasket (P/N: B6BF-13-655) and the ISC "gland" gasket (P/N: B551-13-W89).

* you will have to remove the throttlebody to remove the ISC.

* there is a two-wire electrical plug on the ISV. Over time, these wires and connector can become corroded. Sometimes cleaning them solves the idling issues. Sometimes the two wires become exposed and touch each other near the plug, this can also cause the ISC to not work effectively.

* USE THROTTLE BODY CLEANER ON THE ISC. Other chemicals may ruin the electronics or seals.

Read below to see if other members have added additional info.


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I would like to add to this as I recently repaired this problem on my 92. Use naptha to clean it. I didn't remove anything more than the air intake off sprayed naptha into the throttle body and into the intake for the control valve I sprayed it in 3 times letting it set about 5 mins each time then waited about 20 minutes to start the engine. Then go drive it for about 30 mins. Now it works great and before I started it wouldn't work at all. You can get naptha at any hardware store home depot etc. Hth.
 

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Something else that may be an idle issue is a bad intake gasket. A simple check is to spray some parts cleaner at the base of the intake runners as the engine idles. If the RPM's pick up; you've got a leak!
(Starting ether works too, but being more volatile use it only if the engine/exhaust is cold)
 

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I recently had issues with my idle and random misfiring. I assumed that it was my coil pack going bad but after cleaning the iscv and replacing the coil with still the same issues I did the carb cleaner trick with spraying around the intake manifold gasket. After doing so with still no leaks found I spraying down at the injector seat seals and found my leaks!
 

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How about this:

I usually have a bad "blurpy" idle, nothing crazy like way up n down in RPM's, just like blurp...blurp blurp. I also have stalling issues off throttle! Usually this is caused by the dash-pot/damper on the 1.6 TB but I've gone through 3 of them and the problem still persists.

Will the IACV cause off throttle stalling like this? I already got a new IACV gasket from a junkyard car (lots of Mazda's share the same IACV. BP Protege's, Escort GT's MX-3's) and may grab and extra one to clean just in case I mess up lol.

I just want to know if this will cure my stalling problems or if it's a matter of timing. (plugs and wires are new too)

Either way I'm going to clean it.
 

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I've read, and continue to find articles on this issue. The only thing left to do is to go through the Idle Speed Control troubleshoot as detailed by Ross Kuhre in the Garage section of Miata.net. This is a big job. If there is something else I should check before jumping into the ISC, please give me some input.
 

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I just bought a 91 na that sometimes does it at a red light. have been researching and just joined and checking out the site and found some really good ideas. this has been one of the best sites I've ever stumbled across....finding so much info here
 
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