Are these cars automatics? If so, an engine misfire will put the transmission in limp mode to protect the engine, and you will not be able to get top gears or overdrive.

Also, I forgot a couple of real dumb things that crop up so rarely they are overlooked (by me at least).
!. Pull your PCV and shake it. If it rattles, good; if not, replace.
2. The whole ignition system performance hangs on an inconspicuous black rectangular box thing called a capacitor hooked up to the + line of the coil packs on one side, and grounded to the engine at a point near the coils somewhere.
When the coils are triggered, the pulse current is too heavy and rapid to be efficiently supplied via all the wiring going back to the battery, so that capacitor works like the flash unit in a camera, temporarily providing a short direct path for the huge current pulse essential for a hot fat spark. If that sucker goes open circuit, the spark will be seriously degraded on all the coil units it supports, and it does not show up as anything distinct, just contributes to a general malaise and misfire under load situation. It is not expensive to replace.

 

my millenia s with 52000 miles has similar issue. noticable hesitation under medium to heavy acceleration at higher rpms. no check engine light.

while in park or neutral, revs nicely. does have a very minimal vibration at around 2500 rpm's

replaced plugs with ngk's suggested on this site, fuel filter, air filter. have not yet replaced coils due to cost. is there a way to test the capacitor?

help

 

My 2001 Mazda Millenia S recently started to show the TCS Off/On lights and wont allow me to accelerate. I feel like this mainly happens when I go up hills. Do you think changing the plugs and leads will help that out?

 

there is no external capacitor on 2.3 ign system. it is a coil-on-plug(cop). i would bet it is a weak coil, which is really hard to find, since in early stages, it will not throw a code. i think the only way to test them is with a scope, and that would be impossible because of the locations of the coils. look at this:

How To Test Your Coil Packs - Mazdaworld

this may work, but you also need to test the diodes in each coil. the bad part about all of this is that you need to pull the coils, and that alone is almost not worth it. what i did was take a known good set of 3(we have 2 99's, so i could pull 3 coils off at a time), and install them on the front bank first. the front bank is really easy to get to. then go for a test drive. if you are lucky, this will solve PART of the problem, like it did for me. to be really sure, install the coils in again, or in another car(which i did) to see if the problem returns. if it does, then you know it is a coil. now you have 3 coils, one of which is bad. if you want to find it, you gotta replace 1, test drive, etc. which means you pull off the same parts 3 times, max. i found it on the second try. now, if the front bank shows good, then you gotta pull the rear bank coils, which is a paininthebutt job. i didnt have to, but i was prepared to install 3 known good coils if i had to. i have a drawer full of coils, at least 2 full sets, so it is easy for me. you might check with a junkyard, or ebay, and hope you get a good set. a new coil is expensive

 

again, 2.3 does NOT have ign wires. most of the time, if the problem is plugs/coils, the ce will flash, but it will not go "limp home" which is what your car is doing. your problem is most likely a vacuum system leak, most common is a broke plastic "tee". this causes the abv to malfunction, and the pcm then puts the car in "limp home(car wont rev above about 2500 rpm, tcs off/tcs lites up on dash)". very common for the 2.3. you have to find the leak. the best way is to just replace the tees with brass-you can find them at a pet store, in the fish section-and new silicon lines(21+feet) from anyplace that sells turbochargers. this is a labor intensive job, the intake has to come off, and you have to be VERY careful on reconnecting the lines. also, there are 2 solenoids(vacuum and vent) that control the abv, and they go bad. they cost about 62 bucks each(tasca parts, online), and they are easy to test with an ohm meter. if i were changing out the vacuum lines, which i did on both cars already, i would also replace these 2 solenoids, since they go bad all the time.