1992 Mazda IDLE TROUBLE

The problem.. when stopped the idle dips from around 900rpm to maybe 300rpm. Does this for just a little while and then dies. Sometimes when I pull up to a stop it seems to idle just fine and then dips down and bingo bango it starts to die.

What I have done... is replaced the fuel filter, spark plugs, spark plug wires, air filter and oil. Instead of helping what used to be a dip... now it dips and dies.

Besides this dip & die problem my mazda runs just fine... zoom zoom down the highway.

Any suggestions on how to troubleshoot this problem?

Thanks for your time!!

http://www.miata.net/garage/isc.html

I had an odd problem where one of the pulleys had rubbed a whole in the plastic intake plenum and caused this. Near the throttle body, you will see where the intake dips down to create an extra chamber. Look at that closely. Then do what Sam says.

Another vote for the ISC Valve! (Sammmm's link)

I started the troubleshooting process and when it came to the part concerning "ECU Codes", I get a 17 for Oxygen sensor. I replaced the oxygen sensor with a Bosch universal Oxygen sensor kit however I am still receiving the same 17 code. Not sure of my next step. Unable to proceed with troubleshooting the idle until I solve this Oxygen sensor issue. I jumper-ed out the 10-grnd as directed to receive the code.

Do I first clear the 17 code using the battery?
Do I replace the universal sensor with a OEM?
Do I search for a bad connection or open within the Oxygen sensor wiring? Will need diagram to troubleshoot.

Was hoping replacing sensor would have solved the 17 code problem..

thanks for any help in advance

mims

I'd clear the codes with the battery first. Cheap, simple and can give you a clean slate. If it throws the code again, start chasing sparks.

Code cleared... now troubleshooting the idle.. i changed out the spark plugs, fuel filter, spark plug wires.. and ever since then it will not idle. So i working through the instructions.

thanks

I can't tell. Did you or didn't you change the ISC valve? If not, do that. Check with Track Dog or FM for used ones if you want to go cheaper than new.

Quote:

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Originally Posted by cwisenheimer

I can't tell. Did you or didn't you change the ISC valve? If not, do that. Check with Track Dog or FM for used ones if you want to go cheaper than new.

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No kidding. New ISC is $$$$$.

These are robust little devices, but I had mine jam up on me a couple of months ago. A bit of carb cleaner and some light oil got it working perfectly again. If the coil is good (check for 12 +/-1 Ohm), it's probably just some easily cleaned buildup. Only thing you'll need is a new OEM gasket. Easiest way to remove the ISC is to remove the throttle body. Then you'll have good access to the 3 phillips screws that hold the ISC to the throttle body. Once off the throttle body, it's a piece of cake to clean/unjam the mechanism.

My car will go over 209K miles this weekend BTW -- just to give you an idea of the mileage that causes buildup. I also use water injection -- probably doesn't help.

I took off the TB and removed the ISCV. Cleaned both with carb cleaner. OHM reading on the ISCV was...... 11.8 so i reinstalled. I did not replace the gasket. Not sure what gasket i should have replaced. the rubber one between the TB and the ISCV or the paper gasket between the IM and TB.

When cleaning the ISCV it appeared it was stuck.... so i loosened and reinstalled the ISCV. haven't started it yet but planned on tomorrow. Let me know if i need to replace gaskets... the rubber one between the ISCV and TB looked still good but if i need to replace will have to find one.

I am hoping to get around 200k miles on this vehicle before i have to perform any major rebuilds . I purchased this miata with only 116,000 miles on it.

This is my first miata and one of the reasons i purchased the vehicle is so i can perform my on maintenance. I have lots of tools and some skills but no experience with miata and fuel injection.

Once i get this engine problem solved i will need to replace the top... I tore the back window zipper off and now i have no protection for the rain. bummer.

Thanks DFW miata forum for giving me a helping hand !!!

As a general rule, replace all gaskets you encounter. The gaskets are Mazda parts readily available from Mazdaspeed, local dealers, or online dealers like Rosenthal.

But, since you've got it back together, no harm in starting. If the ISCV gasket is leaking you'll have a coolant leak. If the throttle body gasket is leaking, you'll have lower than normal vacuum and perhaps additional roughness (as if it isn't rough enough).

BTW, you have thoroughly checked for vacuum leaks, right?

Hummm.... so i reinstalled every thing and..... it works. I adjusted the Idle speed screw all the way down and her idle is around 850. I guess the ISCV was stuck. I will see how she drives over the next few days.


If ok.. then the next repair is to replace the top.. How many full days should i dedicate for the top replacement. Also,, should i purchase top online or purchase local. If local,, from whom?

Thanks DFW miata for all your help.!!

Top replacement isn't too bad but wait for warm weather to do it.

I bought my Robbins top on line from GoMiata. Like sammm says, it's much easier to stretch the top into place if the top is warm.

And plan for several hours if you have not done one before. May want to consider replacing the rain channel as well while you have it apart. Cheap insurance for the future.

Also plan to change the tension cables.

Ok... Its been a few days and the Idle seems to be just fine. next projects are.

replace clutch and top..

thanks again DFW miata forum !!

Clutch isnt to bad. Plan to change a bunch of little hoses and seals while you're in there, save you a ton of headaches later.

Clutch isnt to bad. Plan to change a bunch of little hoses and seals while you're in there, save you a ton of headaches later.

Any plans for FI? If so, nows the time to upgrade to something like an ACT Stage 1.

If not upgrading, I'm surprised that you need a clutch at "only" 116K. Seriously. What are the symptoms that make you think a clutch is needed?