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.

[@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!

[@built2build600]

I appreciate any input you can give. What strikes me as unusual is the sound entirely resolves once the engine is warm. Would that direct your diagnosis? How would you proceed?

[@DaJoJomason]

@@built2build600 If the whine goes away when warm, it could be a bearing instead, maybe the alternator bearing. On top of the belt tension, I would check all the pulleys and see if any are shot. Works out a little because you can just remove the belts to check them, and then tighten the belt to spec afterwards. You check the bearings by spinning the pulleys by hand, once the belt is off them. If they're gritty, give some kind of weird resistance, or make a sound when spun by hand, its bad. You can listen and rev the car from the engine bay (or place something on gas pedal) to try to figure out where the sound is coming from before your mess with anything. The alternator bearing is one of the more likely ones that can fail, and can easily be damaged by overtightening the accessory belt. That's sadly the problem with these manually tensioned belts, too loose they slip and too tight they wear out your bearings. Getting the belts off is not terribly fun. Basically you're going to remove the intake cross over and then loosen 3 bolts per belt, there's 3 on the alternator and 3 on the power steering. 2 locking and 1 tensioner each. Crack the locking bolts loose and then use the tensioner bolt to tighen/loosen. install in reverse, tighten to spec then tighten locking bolts. One of the alternator's locking bolt is accessed easily underneath the vehicle with the undertray removed, and the power steering pully has a cutout that needs to be in the 8-10 o clock range to expose one of it's locking bolts.

[@DaJoJomason]

@@built2build600 Most miatas will have a slight ticking sound until warmed up, but should not have any whining or high pitch sounds.

[@built2build600]

Thanks! I will check into it.

[@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.

[@ChutneyInc.]

Accessory belts too. The alternator belts need to be super tight. Like pry the alternator with a lever while tightening tight. Ask me how I know

[@valhallaholsopple]

@@ChutneyInc. You are correct. And that would be the easier one to check.

[@meinungsfreiheit2023]

This happened with my MX5. TIMING BELT....

[@davidoff59]

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

[@B0BACAKES]

Would you happen to know the equivalent in a 1.6 model?

[@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

[@Matt_A4]

How’s it working

[@JAPerror]

Update ?

[@Oisinohneill]

Update you sausage ??

[@vidademikey9790]

Bro, update? Hmm??

[@Surms41]

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.

[@thomasriosgamer]

Duuuude I experienced the same exact thing and I’ve replace almost every sensor and I’ve gotten to the point of replacing my intake manifold but we’ll see how it goes!!

[@ChutneyInc.]

I've replaced everything idle and intake wise. Coolant temp was replaced too my ecu still blaming everything. I don't think I have ever changed the cam sensor but I've been thru several crank sensors for various reasons. Coolant sensor from autozone isn't working so I ordered a Mazda unit well use dielectric grease when I out it in. Also have new crank and cam sensors on the way. No vac leaks in pretty sure. Replaced every line

[@ChutneyInc.]

I'm thinking I have a bad cell or messed up some diodes. It all started with a bunch of alternator belt snaps. U really have to tighten it more than u think. Like while prying with a lever while tightening. Or it's gonna snap

[@ChutneyInc.]

Yup dead cell. Vatozone replaced the battery. And I'm idling normal. And back to "trying" to behave behind the wheel. I am so happy. After all the hard work and money saved refreshing everything from sensors, seals, o- rings gaskets, hoses, seals, pulleys, belts and more belts..... my DIY has earned 100,000 miles of smiles! 🍻

[@Surms41]

@@ChutneyInc. happy to hear bro! I'm currently down. Cars been in the back yard for 3 weeks, trying to find the motivation to replace my water pump and tentioners for the timing belt. It just snapped after I replaced it about 6 months ago :(

[@dansotelo228]

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.

[@SilviaLover2012]

What is a cam index sensor

[@dodgeplow]

@@SilviaLover2012 cam angle sensor. It's on the back of the engine. it is very much like a distributor without the spark wires - it runs off the cam and you rotate it to set ignition timing (with a timing light)

[@TwOxSiDe]

I found that out for myself the ignition coil was causing a misfire on one of the cylinders it's actually fun fixing miata engine problems

[@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.

[@CharlieFrancis-x8b]

Alternator bearings are almost siezed, that's what the whine is.

[@6Slick6Rick6]

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 🤔.

[@roadrunner594]

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

[@roastytoasty4451]

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

[@johnnycee5179]

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

[@AESmith-pr9xm]

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

[@lizboot7431]

Mass airflow sensor

[@likesomeboodee]

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

[@diosdadocabugao68]

Whining sound is your timing belt

[@built2build600]

I later had a coolant leak so changed the water pump and timing belt. No more funny sounds or leaks. Great little car.

[@valhallaholsopple]

I believe you're correct about the timing belt

[@tedhibbard6320]

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

[@ybarsabal]

part out