Bouncing Tachometer Needle When Accelerating

Hi all, new poster here! I hope I didn’t miss an answer in my search.

I have a 2010 Mazda Miata GT that sort of out of the blue developed this issue with the Tachometer/engine acting irregular during acceleration. It’s most noticeable on sixth gear and not as noticeable on first/second but I’ve caught it doing it on the intermediate gears as well. You can watch a video here:

One sure-fire way to recreate the issue is to take my foot off the gas and coast for a few seconds, letting the RPMs drop, then apply steady pressure on the gas. It’s also particularly noticeable on hills, where it will bounce pretty much the entire time I’m climbing. It’s not as bad after I get past about 3.5. The engine noise indicates that it’s not just an issue with the needle. The only thing on the car that I’m aware might even be a little flaky is the battery; otherwise, she’s about 75,000 miles and seems pretty healthy.

I did a little basic internet research and some sources indicated that the TPS might be to blame. So I got myself a little Bluetooth OBDII reader and app an managed to catch it in the act. You can see my results in the attached picture, which also checked MAF. It definitely looks wrong! But my mechanic says he’s never heard of a Miata with a TPS issue. Is this definitive evidence that I have the right culprit?!

OBDII Meter Image:


Your symptoms seems to point to a worned clutch.

Yup. It’s starting to slip. Get it fixed now, because it won’t be long before it’s slipping so much that you’re no longer able to get it to the shop under its own power.

Agree with the other posters, especially

Because you won’t do as much damage so it will be a bit cheaper.

But there’s no clutch involvement. This happens only when I use the gas, not changing gears.

It’s when you accelerate that the most stress is put on the clutch. In any case there are lots of simple tests to check for a slipping clutch.

There IS clutch involvement… the clutch transfers the engine torque every time the car is moving.

Ah…it’s my first manual and my first time really trying to diagnose, so I’m learning a lot. Thanks guys! To the shop!