Diagnosing the Rough Idle on My Miata MX-5

[KaiForce]

Found some cool steps to diagnose your startup whine:

It's a pulley. It could be the timing belt tensioners, ac compressor pulley, PS pulley, or alternator pulley. I think that's all of the accessory pulleys on there.

Normally, we would grab a stethoscope with a long tube extension instead of the usual pad like doctors use and hold it as close to the pulley as we can on each individual component to find out which one it is. If you don't have access to a stethoscope, here's what to do:

First off, try tightening all of the tensioners (read: alternator and PS brackets) a bit. If that doesn't work, get new accessory belts (if they're original, you probably need new ones anyways) and put them on, properly tensioned of course. If it STILL makes noise, do the following. Pull off your ac and PS belt and turn the engine on. If the noise goes away, it's one of those. If it's still there, take off the Alternator belt (keep a jump box or extra car and cables nearby, just in case). Again, if it goes away, it's the alt, if not, it's probably your timing belt tensioners. You'll probably have to replace whatever component it ends up being.

[valhallaholsopple]

The whine is probably caused by the timing belt adjustment. It's supposed to be 19 teeth between the exhaust and intake cams. The timing belt is too tight between the cams. The car passion channel has a good tutorial about changing the timing belts.

[davidoff]

By disconnecting the MAF, you default to a base map just to correct the terminology used. It doesn't go into limp mode

[PixLWeArePixL]

So mine is running real poor idle too. I changed all the hoses, PCV, cleaned the throttle body and MAF and still idling poor. Summarized it to replacing the MAF or the Idle control valve. Let’s see, I already ordered both parts. It’s just matter time

[DaJoJomason]

That's amazing that you managed to fix the idle so fast, hopefully any other problems are just as easy to fix. The whine did not sound that bad now, compared to before, though I do not know what it sounds like from the engine bay. If you can clearly hear a whine that the camera isn't picking up that well, the most common causes of whining sounds on these miatas are the belts. Usually the accessory belts being too tight/too lose, the timing belt being too tight, or the timing belt rubbing on one the plastic covers. I believe you said the engine was taken apart in the past for a head gasket, which all three of those belts would of had to of been removed to do so. The belts have a decently small window for the correct tension, with the timing belt having separate marks to time and tension properly. One of those belts could easily be the problem if they didn't tension them properly when reassembling the engine. I wish you luck!

[dansotelo]

OK, I have news for every frustrated Miata early model owner(s). I too went thru all the hardship trying to figure out rough idling or just won't start etc. on my 1990 Miata... So I broke down and took it to a Miata $pecialist... Here were my problems: 1, My car would run great but as soon as it reached temperature it would stall and die. 2, the interior fan stopped working.
I was shocked by what the mechanic replaced and had my car running like new. 1, he replaced the ignition switch, and suddenly my interior fan started working again. 2, he replaced the cam index sensor, something I would have never thought of going wrong. These two things simply eliminated any and all of my problems it had and runs like new, just amazing.

[Surms]

Mann, I spent almost 3k on a NB 1.8, guy didnt say theres a loose crank and I just rebuilt my keyway by hand. Now Im solving idle problems that werent there before cause he turned the idle way high to combat the poor idle due to bad timing from a bent keyway. Almost solved. Running it without ECU timing atm.

[Taffey_Lewis]

Nice Nardi Torino wheel... I have the Momo wheel and Torino gear shift. :)... I am switching out my stock seats for Momo racing seats to give me a little extra leg room.

[roastytoasty]

Cheers I’ve been looking for a video on this. I have the same problem atm so I will order a new MAF.
Mazda dealership we’re going to charge me £600 for it phaha. Not happening

[SlickRick]

My sounds like a monster truck when I turn it on and doesn’t stay on, and there was a lot of smoke coming from the shifter area/ maybe by the dash but not in the engine bay 🤔.

[johnnycee]

You have a belt too tight, that's the whine, maybe power steering empty or very low. That's a 5 speed or automatic?

[likesomeboodee]

Anyone know what $20 part he replaced? Part number?
MAF are $130

[roadrunner]

Btw did u get a chance to replace your coolant reservoir? as they will fail and cause massive problems when they do

[AESmith-prxm]

What is the name of that part? Trying to look one up for 03 and don’t know what’s it’s called

[tedhibbard]

Idles better but has no power I bet.Find the deep engine noise With a stethoscope.It sound bad.