I've been noticing a very slight hesitation/stuttering/fluttering loss of power for the last few months. It was super faint and it made me question if I was imagining it, but today it got worse, and confirmed something wasn't right. It is rhythmic, but inconsistent. It fades in and out.

I'm pretty sure it isn't misfiring. No codes, replaced OEM plugs & wires 7k miles ago, and this only happens in 3rd gear, and is most pronounced when cruising at 2000-2500 RPMs.

Search leads me to believe then it is either my clutch or transmission? Both are areas I'm not super familiar with, but eager to learn.

Clutch was replaced with a napa one 50k miles ago, clutch fluid was replaced again 9k miles ago on a mechanic's recommendation after a full inspection. Is 50k normal for a clutch? I think the first one was original that lasted 250k miles. Is 40k interval for clutch fluid normal? or might it point at abnormal wear? Last time the clutch went it was very loud, no noises this time.

Transmission is original, I don't have record of the transmission fluid being replaced, and I can't remember getting it replaced ever. Would have expected that to be called out in the full inspection mentioned above. Should I start by replacing the transmission fluid? Seems a bit more reasonable of an explanation if only the gears for 3rd are gunked up?

Thank you for any help!

Clutch fluid condition does only affects clutch operation when disengaging the clutch so that would not be part of your problem.

50k miles seems very short for clutch life if driven correctly. Typically when a clutch starts to slip it’s most noticeable in lower gears due to the greater torque multiplaction from the lower gear ratio vs higher gears/gear ratio.

Do you have any way to monitor throttle position sensor while driving? I had a bad throttle position sensor that was worn in a small percentage range (17.2-17.8 percent if I remember right) and it would read much lower in that worn area causing a stutter/shutter type feeling.

Thanks! I do have an ultraguage. Just drove around and tested and am not seeing the number fluctuate at all—held steady around 16% when cruising at 30mph. It is most pronounced around that range, but I do feel it at different %.

One thing I noticed this time that wasn't as clear before is that IS rhythmic, but not consistent. might fade or come back, but is on tempo wa-wa-wa-wa-wa........wa-wa.......wa-wa-wa-wa..... etc. this happens throughout it being at a steady TP% I've noticed a similar oscillation in the engine sound while cruising, but without the stuttering.

I did notice the short trim varies +/- 3%, but I think that is normal? It also only feels like momentary loss in power, not up and down, which is what I would expect if it was bouncing between rich/lean?

Short term fuel trims will vary. I see as much as +/- 10% between shifts or releasing the throttle in gear. Maybe someone with a 3RZ/manual will chime in with some things to check. Only one I can think of is @UnderFire

Never seen this problem. Does it do it when you have cruise control on?

50k is a very short life for a clutch, it should be well over 100k miles. Did you replace anything else when you did the clutch?

The only problem I had with my W59 was grinding when going into 5th, especially when it was cold. I replaced the transmission fluid and the problem gradually went away.

@Pyral Don't have cruise control.

Unsure what all was done with the clutch, as it was 5 years ago and it was done by a mechanic. Looking at the receipt there isn't much detail except that napa kit and that the flywheel was resurfaced.

I'm leaning towards starting by replacing the transmission fluid and seeing how that goes, but it shifts great, and never slips out of gear, so that may be a dead end. But it probably has been 100k miles since the transmission fluid was replaced, so all in all not a bad idea.

When it happens do you notice rpm’s increasing or decreasing? Do you feel any sort of lurching or decrease in speed?

Yes, lurching is a better word than stuttering. when it first started happening I wasn't sure if it was bumps in the road or lurching. Feels like a momentary decrease in speed and very slight decrease in rpms.

I just went and tested it some more and do notice that if I slightly take off/on the gas it gets more pronounced. But only for that slight acceleration/deceleration. If I am accelerating normal it feels steady.

Transmission fluid should be more replaced more often than that, but I doubt it caused your problem here.

Does the lurching feel similar to what happens when your about to stall?

Also how is the fuel system, maybe it's stuttering because the engine is momentarily starved of fuel

This doesn't sound like a problem I've run into with any of my RZ's unfortunately. But does sound similar to a problem I'm currently having with my V6 truck. Please do let us know when you've figured it out.

The lack of a check engine code only rules out a hard ignition or injector related misfire in most cases.

I would start with the free stuff. Clean your MAF sensor, clean the grounds for the engine harness (one on coil pack bracket, one on intake manifold and one on back of head above exhaust manifold). Make sure you don't have any damage to the coil packs where the plug wires hook on, I've seen a couple burnt up from sloppy fitting plug wires.

You don't have any issues with hesitation below 3500RPM at WOT do you?

Replaced the fluid, didn't look horrible, but glad I did it. No changes.

Only thing I've done to the fuel system is replace the filter about a year ago. Not sure how the rest of it is, anything you recommend checking specifically?

I cleaned the MAF, TB and IAC about 18 months ago, so those should be fine, but I will take a look at the grounds and coil packs, thanks for suggestions!

No, at WOT at any RPM is smooth.

I'm w/ Bad Luck on this one....my 98 was doing same thing and two so called 'toyota' mechanics couldn't figure it out. After researching it on this forum, of all places....it was the TPS!
I replaced w/ OEM two years ago and have not had that problem since. (the bad one was new aftermarket one). Not saying this is your problem...but worth looking in to.

Thanks! Might be worth a $100 gamble to swap in a new OEM one. I was thinking of trying a cheap $10 aftermarket one, but considering you had an issue with a new one, gives me pause. Though I expect if the aftermarket has issues they would be a slightly different feeling than my current one so I could at least narrow in on that being the problem or not.

@Bad Luck @TracyNorton bit the bullet and swapped in a new OEM TPS. Unfortunately no change except idle reading now at 11% vs 11.8%. Was only $60...was looking at the wrong part number at first, ended up with 8945235020 At least I now have a spare one? lol Getting those screws off/on was a mild PITA though...ended up using a phillips bit in visegrips.

@UnderFire Regarding cleaning the grounds—I tested the resistance between the battery negative and each ground and all were low. I assume this is an indication of proper connection to the chassis?

Checked the plugs and all looked clean.