DestLuck

Alright i have a 2005 Rx8 GT.

It goes in storage every winter and i do a oil change before i take it back out every summer.

Modifications:

- BHR coils
- AEM cold air intake
- Red top optima battery
- New tires biggers size


Problems:

- i start my car and leave it stand for a while and the REVS seem steady at about 1k. Then i turn on the AC or heating and the car seems to have a problem keeping its REVS up. Almost looks like the car will stall, it starts shaking and acting weird.

im not sure what is causing this problem but i would really love to solve it.

RIWWP

iTrader: (2)

Do you have an OBD2 data source? If not, grab a bluetooth or wifi one from Amazon and pair it to your smart phone.

I bet something is up with your fuel trims.

Either way, clean the MAF, the ESS, reset the ESS profile, and reset the fuel trims. After clearing them, the the car idle warm, and then idle for another 5 minutes to rebuild idle trims. Then see if your problem persists.

If it disappears initially, but then eventually comes back you probably have a vacuum leak. This can also be confirmed with the OBD2 data if you get that adapter.

If it never comes back, it was probably just a dirty MAF.

DestLuck

yes i have the app dashcommand and the wifi thing to link it to my phone!!
But not sure what to do with it haha

RIWWP

iTrader: (2)

Nice! Good to see you are have already taken that step.

I don't know dashcommand app well, but see if you can find the sensor feeds for
STFT (Short Term Fuel Trim)
LTFT (Long Term Fuel Trim)
MAF (Mass Air Flow)

With the car idling (must be fully warmed up) and AC off, see what those numbers are. They should be pretty stable, but if you see a range, note the min, max, and where it sits most often. Record RPM too just for a reference point. Also pay attention to when the fans kick on and off, they can change the numbers as the alternator load changes.

Then turn on the AC and record what they are now at.

Come back and post it up here.

DestLuck

perfect ill take care of that when i get off work

BigBadChris

iTrader: (4)

Mine is doing something similar, thanks for the instructions RIWWP. Sounds like a good place to start.

DestLuck

Ok

A/c off car on idle:
- LTFT : -6.2
- STFT: -5.5
- Mass air flow: 1.260

A/c On car on idle:
- LTFT: -6.2
- STFT: -3.1
- Mass air flow: 1.294


Not sure if the Minus is normal or it might just be the way my DashCommand is configured?
hope these help

RIWWP

iTrader: (2)

the MAF is.... impossibly low. A no-vacuum leak normal engine will have a MAF value at 5.5g/s. Is there a caption noting the units of measure on Dash Command? I suspect that it is a voltage value you are giving.

Your fuel trims can be negative. +25% to -25% is the range for each. Negatives in both suggest you have a MAF problem, probably just dirty.

DestLuck

Ok ill try to find the post on how to clean it and then recheck the values..

Thx RIWWP

RIWWP

iTrader: (2)

Always reset fuel trims after cleaning the MAF, fixing vacuum leaks, or replacing O2 sensors.

And let the car idle for a bit after it gets hot to rebuild fuel trims to avoid most of the 'stalling near idle' that can happen after freshly clearing fuel trims.

DestLuck

hmmm ok alot of things to learn then haha.

- how to reset the fuel trims
- how to clean a MAF
- and fixing a vacuum leak not even sure how to find it

RIWWP

iTrader: (2)

Don't worry about a vacuum leak right now. I don't think you have one. A vacuum leak would show low MAF values (usually 4-4.5g/s) and POSITIVE fuel trims. You have negative fuel trims, which means the front O2 is seeing too much fuel for the amount of air your engine is actually consuming. A fuel injector sticking open could do it, but usually sends the trims much farther negative. It is more likely that the MAF is just over-reporting how much air is going to the engine, so the ECU is fueling for the falsely high airflow, and the O2 then sees rich, and cuts fuel to compensate.

DestLuck

Aww ok that clears it up a bit thx for the info... searching the forums for the DIY maf clean :D

DestLuck

alright i reset the fuel maps and cleaned my MAF with a cleaner used for sensors.

i started the car and let it sit and warm up on idle for about 5minutes.

Car warm on idle A/C off:

- Engine temp 154C
-LTFT: -6.2
-STFT: -0.0
- Mass Air Flow: 1.191

Car Warm idle with A/C on:

-LTFT: -6.2
-STFT: -0.8
-Mass air flow: 1.182



I also added a gauge to see the cata temp and this is what i got: 605.5c

Car still seems to have a semi rought idle.?

RIWWP

iTrader: (2)

Is that the only MAF value you can find on the DashCommand? I'm sure that's the voltage, but the actual converted g/s value would be much better to know (and I can't use a calculator, since all MAFs are slightly different, and the scaling relationship is something that can be changed in the ECU)

The fact that it jumped back to -6% fuel trim says that the problem is still there. You want within 5% of 0%, and most cars sit within 2%. At -6%, your actual AFR is probably about 13.8, vs a desired 14.7, so almost a full point off, still getting too much fuel.

It's still most likely a MAF problem. Do you know any other RX-8 owners near you that could swap MAFs with you temporarily to confirm?

RIWWP

iTrader: (2)

Looking through another thread with negative fuel trims, higher positive MAF (https://www.rx8club.com/series-i-tro...-trims-242769/) more severe than yours though.

The front O2 sensor is another possibility. If it only THINKS it's seeing rich. But that isn't normal. Most fail seeing too lean, and your MAF g/s values would still be normal, regardless of what the front O2 is doing.

One recommendation in that thread is force it to open loop ... which I'm pondering the best / easiest way to make that happen. Disconnecting the MAF is one way, but you want it connected for this. Disconnecting both O2s is one way, but the front O2 connector is hot and annoying work to get to (on top of the transmission bellhousing, in line with the firewall)