HELP! Loss of Power Under 4k/Rough Idle
 

My problems described below have been resolved. The majority of the issues were due to a disconnected vacuum hose under the UIM, specifically at the VDI actuator. If you are experiencing issues like mine.. please read on about all the steps I have taken.

For starts.. 2007 Sport Manual.. 83,XXX miles.. mostly stock aside from Injen CAI, installed by previous owner.

For the past few months, I've been experiencing the following issues with my 8:

-Intermittent loss of power under 4,000 RPM (by intermittent I mean that some/most of the time I experience it, but sometimes the car acts normal).. after 4,000 RPM.. the car is a rocket!
-Rough idle - fluctuating between 750-1000 RPM (tach visual)
-Bad gas mileage (12-15mpg) city and highway, regardless of how I drive
-Popping/banging noise in the exhaust which I believe is excess fuel burning off, but could be misfiring (I feel a rumbling feeling when this happens)

No CEL, and furthermore no flashing CEL which would indicate no misfire..


What I have done over the past few months to help diagnose/fix the issue:

New plugs, wires, coils
Cleaned MAF (which wasn't really dirty to begin with)
Checked vacuum hoses for leaks (none found)
Cleaned ESS and reset NVRAM
Installed a grounding kit (which seemed to help marginally, specifically with throttle response)
Removed cat.. installed mid-pipe with cat-delete, has O2 bung..
Seafoamed last weekend as last resort before taking to dealer for compression test.. lots of smoke, but no change :/

Now, I've spent a lot of time of this forum recently gathering as much information as my brain will allow me.. and I've learned quite a bit. Everything that I've done so far, is due to what I learned here.

Also I learned that if I didn't do the above, and came here to ask questions, you guys would tell me to do the above or "USE THE SEARCH FEATURE!" Lol

Since I have not remedied these issues, I took the car to the dealer yesterday for a compression test. Mazda told me that they would do a "Full Circle Report Card" for $79.99 which includes a compression test. They said if the compression is good, then they will tell me what IS causing the problem. I said sounds great.. win/win!!

Compression test results:
Front: 7.6 / 7.5 / 7.7
Rear: 7.2 / 7.1 / 7.4

^I was very happy with that, and so were they..

The problem now, is that they are telling me they cannot complete their diagnostic test due to the missing cat. It's "throwing off signals and sending our data all over the board" -they said.

The tech told me that he feels everything is good.. coils/plugs were good, etc.. etc. He said that the ecu isn't giving the engine a proper "tune" because it can't get a correct reading due to the missing cat. I argued that before removing the cat, the issues were still present. Then he argued that removing the cat would void my warranty, so I shut up..

I think that is bullshit, but then again, what do I know? It's my understanding that the O2 sensor that plugs into the cat is just to test the performance of the cat/make sure it's working. It's also my understanding that the O2 sensor BEFORE the cat is the one that is used to help measure air/fuel, etc.. So is what he is telling me correct?

If not.. how do I "fix" the "tune"?

What other items should I look over that I may have missed?

I ruled out a stuck SSV, since I'm not getting a CEL.. should I check it?
Even though the MAF is clean, I guess it's possible that it's not working.. how can I check this? I have a multimeter.. but don't know how to check it.
The O2 sensors might need replacement, but those are costly.. any way to check these before purchasing?

I appreciate your time reading all of this.. and if I left anything out, let me know

Thanks, guys!

Also might be worth mentioning my clutch issue..

Clutch itself is fine.. has a good bite, no slipping.. but the engagement point keeps changing/moving around, despite the fact that I've bled it on multiple occasions. I'm targeting the slave cylinder, and if I replace, I'll also go with a stainless steel line, but thought it might be worth mentioning this in case it could somehow possibly have something to do with the other issues.

The pedal is wobbly and probably about to snap.. the dealer didn't want to replace and told me it isn't under warranty. I called Mazda Corporate and they told me it was indeed under warranty, and they called the dealer to tell them.

They now agree about the warranty, but still won't replace it because it isn't broken yet. I'm going to take it to Classic Mazda in Orlando next time.. I hear good things about that dealer.

Maybe dying fuel pump/ dirty sock?

You know.. I thought about that a couple weeks ago, and forgot..

I'll give that a check this weekend, thanks!

Subscribing to this thread. seems i have aaround the same issues as you. :https://www.rx8club.com/series-i-tro...9/#post4499093

Anyone?? Come on guys.. I know someone here has some more suggestions!

I bought a bluetooth OBDII reader, and downloaded the Torque app..

Getting a P0420 CEL.. Because of the missing cat.. no big deal. I did a little research and a few people suggested that this will not have any affect of engine performance..

Ran a test in Torque.. here are the items that said "FAIL":

Mode $06 report generated by Torque for Android ================================================

MID:$21 TID:$80
- Catalyst Monitor Bank 1
Max: 7.9999Ratio Min: 0Ratio
Test result value: 10.81627Ratio
FAIL
----
MID:$90 TID:$05
Rich to Lean sensor switch time(calculated) -
Max: 0 Min: 6,177
Test result value: 65,520
FAIL
----
MID:$b0 TID:$99
-
Max: -74.38335% Min: 25.19731%
Test result value: -79.93798%
FAIL
----
MID:$f0 TID:$cc
Manufacturer defined MID -
Max: 2 Min: 8,273
Test result value: 52,464
FAIL


I searched around and few others posted similar results, but not much direct feedback regarding whether or not these failed items are contributing to the issues that I'm having..

Anyone know how to read these better than I do?

I bought a new MAF and an expensive ass AFR O2 sensor.. I'll report back tomorrow with my findings. I will also check the fuel pump and sock, as BigCajun suggested. If I have no luck after both of these new parts, then I am really at a loss here.. so if anyone can chime in with some more info, I'd be extremely appreciative.

Thanks!

That 2nd test tells me your front O2 sensor is dead. The replacement should help a number of things.

Your prior comment was generally correct. The front O2 sensor is the one that handles closed loop AFR data. The rear O2 sensor is used primarily for emissions verification, although the ECU will use it to refine AFRs during stable cruising conditions as narrow band O2 sensors (which the rear is), are faster to respond than wideband (which is what the front is). The rear O2 sensor has zero impact on power production while accelerating.

Awesome! Thanks for the input! Just ordered the O2 sensor today with overnight delivery for tomorrow. As soon as it's delivered, it's going straight in!

I'll report back with [hopefully] positive results!

Thanks again! :D

Good luck! If it works i'll definitely thing that maybe that might be my issue as well!

I'll keep you posted.. Hopefully the O2 sensor is the issue, and hopefully that will solve your problem as well.

As soon as I install it and test it out, I'll get on here right away to let you know how things went.

Hi andrew, I was just guessing. Looks like R's got you pointed in the right direction.
I have the Torque app also, it's an amazingly effective tool.
Luckily, I got my initial problems straightened out with R's & others' help, so all I've used it for is clearing 420 code,(BHR midpipe) & monitoring Coolant temps, ( knock on wood).
Good luck!

Any word yet I know its early haha.

Front O2 sensor did the trick!!

Was out all day.. got home a couple hours ago and the package was at my door.. installed it right away.

What a difference!! Idle is really smooth now, and the power even in the lower revs has drastically increased!!

I also noticed that the engine starts much easier.. seems like it's putting less stress on the starter. Fires right up without a fuss!

Hope this solution works for everyone else with the same issues that I was having..

Let me know if you guys have any questions!

Thanks for all the help!

Looks like you're a happy camper! What sensor did you wind up going with?

did it clear up the exhaust popping on idle? mine takes a while to start and pops on idle (although stable) and seems to be underpowered below 4,000 also but i thought it might just be normal mapping or character of the car. mines only done 55km (not miles)

I went with the Walker.. I know it's a generic sensor, but it was only about $100 and I read a few good things about it.. and so far it seems to be working perfectly fine!

If it ever dies out, or if it does die out quickly, I'll be sure to let everyone know. And if that time ever comes then I'll just grab to OEM one.

I have Amazon Prime.. it was $107, plus $8 extra to have it next day (Saturday)

No more popping on mine..

I'd say that you might be running a tad bit rich.. and the popping is just the excess unburnt fuel igniting in the exhaust.. Or at least that's what was happening with mine.

But now that I have a fresh O2 sensor up front, my engine is getting a proper tune and therefore no more excess fuel being dumped into the exhaust..

I found a bosch on amazon for 166! :D

So after spending a lot of time with the car over the remainder of the weekend, and today, I can conclude that 90% of my issues have been remedied via the new O2 sensor.

With that being said.. the idle still has a slight roughness to it. It's much much better than before, but it still fluctuates a tad bit between 800 and 900 RPM, with the occasional dip lower (which you can really feel.. almost like it's going to stall, but doesn't).

I think I mentioned previously that I purchased a new MAF.. which I did through Advance Auto Parts online for local pick-up, but I never did pick it up (and furthermore they didn't charge me for it).. I think I might go grab that, to see if that helps.

Also I'm going to do a more thorough check for any vacuum leaks. My goal is to get this thing running in tip-top shape!

I have to add that I am LOVING the power increase from this new sensor! Car feels alive again! Just wish the idle was perfect. I'll work on that and report back with my findings!

To the few people with similar issues who've been following.. let me know your outcome!

Installed a new MAF.. no change. I'm just going to return it since mine is apparently functioning properly.

Idle seems to have gotten worse throughout the day today. It doesn't fluctuate as much as previously, but it's quite rough.

I just want to fix this!!!! Gahhh!!

It's probably worth noting that when I first start the car (hot start) the idle climbs to about 1300 RPM and stays there for a brief moment. During this time the idle is incredibly smooth and feels as it should. Then it darts down to 900ish RPM for normal idle, and it's rough again.

I've also seen no improvement in gas mileage which seems odd considering I'm no longer running rich like before. If anything actually it looks to be worse. Before I would get about 50 miles on the first quarter tank after a fill-up. I could maybe squeeze 60 miles if I really kept my foot in check. My first quarter tank after installing the new sensor yields me 30 miles!!! That's not right at all.. something else is still wrong here.

I thought about the incredibly small possibility and crazy coincidence that I could have gotten bad gas, but that seems highly unlikely.

I would do two things at this point.
1.) Clean the ESS(although you may have already done it).
2.) Clean the throttle body. No real need to take it off completely, just clean around the butterfly valve real good and make sure it moves freely. Wipe out any excess gunk and carbon deposits.
Use throttle body cleaner if you have some.

Where in Central Florida you located?

Lemme guess, it dips up and down when you kick on the AC too?

I did already clean the ESS, but that was a couple months ago.. perhaps it acquired some more dirt.. I'll do that again today.

I haven't cleaned the throttle body at all.. But I'll do that as well.. Thanks!

I live in Port Orange, next to Daytona Beach.

Yup! Although it's very subtle in comparison to before. With the A/C on, it would always dip down hard; it was very noticeable. Now it's not nearly as bad, but it does still do it.

Yea, mines doin the same thing. I cleaned the ESS and TB and MAF, replacing the O2 tomorrow. I'm hoping a good ground and the sensor will clear it up.