2 things -- trans and engine related
 

So, I have two issues, one trans, one engine.
1. Transmission: sometimes when I want to go into first from second or neutral (traffic, rolling through a yield sign, etc.), I have to double clutch even with rev matching or else it grinds. I can feel the teeth vibrating, so I don't force it, I just pull back to neutral, wiggle the shifter and pump the clutch and try again.

2. Engine: I keep hearing a bearing noise on the right side of my engine. It's audible usually only on cold startup, but definitely has that rolling around, marbles in a mug kind of sound. Anyone else getting this? I feel like I saw something about a pulley nut or something but don't remember.

Actually, maybe 1 more -- TPMS sensor light goes on and off randomly. It usually blinks then goes on after I've been driving for a long time and then goes off whenever it feels like it.

Any help greatly appreciated. Also, if anyone recommends a dealership for service in NJ, lmk.

Cheers,
Isaac

WRT to your TPMS, you didn't mention that you checked your tire pressure. Did you?

This is a common misconception. There is nothing wrong with the transmission most manuals don't want to go into first gear if the car is in motion and you can actually damage it trying to do this. The gear ratios on 2nd gear allow you to take off through a yield sign or any other situation where you are rolling at low speeds and need to take off. Trying to put your car into first gear while you are rolling is not how to drive a manual. Not the car, its driving style that is the fault here.

Sorry for two posts. The bearing type noise I would take to your dealer and get it looked at just to be safe. Can't diagnose it over the internet and you will want to get that stuff taken care of early before it becomes a problem. It is possible there might be a TPMS problem but more then likely your wheels were filled in a different temperature range and the new temperature range it is operated in is causing you to gain/lose pressure. Go buy a 5 dollar tire pressure gauge and check them out for yourself. If they all show 35 psi then ther sensor is bad, but if they show 29 or something then you need to air them up and it won't bother you anymore.

Manual transmissions, and especially this one when cold, don't like going to first while rolling. It can damage some transmissions. This is no flimsy cable operated transmissions, sometimes it takes a firm hand but I definitely would not shift it into first while rolling.

Engine, get it checked. Might be nothing but who knows.

TPMS - its normal for tires to lose pressure when cold. Air is less dense cold. Probably a non-issue.

Going into first at a moderate/slow roll IS FINE if done correctly, but it's typically ill advised as mentioned above, and should only be done with a fully warmed up transmission (10-20 minutes of driving). First gear is really short, so forcing the synchros to make up the huge gap in RPM can cause excessive/premature wear on the synchros. The way to avoid this is not only to rev match, but also to double clutch. Double clutching does the job of matching the speed of the input shaft to the engine, so the synchros effectively do little or nothing at all. Even still, first typically isn't necessary unless you're stopped, or nearly so, or doing autoX with a lot of 1st/2nd corners. A fluid change might help, the full synthetic German-made Pentosin MTF-2 is on the thinner end of the spectrum, but has been getting great reviews for improving shifting feel, especially for 1st/2nd, and especially in cold temps.

The "grumbling bearing", that's an odd one, need more info.

TPMS, could be the tire(s) are low, and after some driving the tire temps rise, causing internal pressure to increase. This increase of pressure may be putting the tire pressure back into the proper window so the TPMS computer thinks everything is OK and turns off the light. I agree with the above comments, get a basic pressure gauge and check 'em. Or, it could be a faulty TPMS sensor/battery which is not transmitting properly.

fixed it for you ;)

For #2, is it when it's idling? Or is it when you're accelerating at below 2000 RPM?

Sorry for gravedigging -- been so swamped at work lately!

Some good info, thanks for sharing the trans tips with me. I only fear lugging the engine at sub 1800rpm speeds.

Sigh-On, I'll have to check on the accel, but I do notice it while idling and a little throttle blip under 2000 rpm.

My TPMS light also came on when the weather got colder(40 degree-ish). On a warmer day (50+ degree) it went away, so to confirm what mhigham said, it is probably just colder temperature that is causing that light to turn on. No big issues, but it doesnt hurt to check your pressure.

True, after I posted the first post, I bought a decently accurate gauge that I keep in my door cupholder (haha does anyone use that for its purpose, anyway?). :D

Update -- The noise that I'm hearing only occurs when the clutch is let out and goes away when the clutch is in. It's like way too soon for it to be a throwout bearing, right? Idk, gonna get it looked at as soon as I get my Miata back on the road. Will update once we figure out what the noise is.

In the cars I had before this, I'd get TPMS every winter. It's the cold weather.

you aren't supposed to shift in to first while rolling. it can cause damage to the synchros.

yes that does sound like your throw out bearing.

Agreed. If you want to hit first you should rev match as any other way could result in damage. Only time I have ever done this is during auto X.

I also agree that the sound you are hearing could be the throwout bearing.