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P5 rough idle... Help!

My DD is an awesome automatic P5 with 183k miles, just barely broke in! The car has been great! I drive 62 miles each way to work 4 days a week and it's been a perfect commuter for a long time!

Here's the backstory... I've been having a CEL code p0455 for awhile now. (Code is a common EVAP code) The gas cap was replaced about 1yr ago, no change. So I dug a little deeper and decided to change the Purge EVAP solenoid. Cleared codes and seemed fixed.
Recently I was noticing a little hesitation in throttle response... no codes... and now the fun begins...
I started with changing the spark plugs. (Only NGKs! Don't waste your time and money with anything else on a Mazda!) Spark plugs had a little oil on the threads so I changed the valve cover gasket and PCV valve while I was there.
Then I cleaned the throttle body with ONLY throttle body cleaner. While there I decided to pull the IAC and noticed it was a little dirty and looked original, so I replaced it along with a new gasket.
Now I start to get a rough idle and almost stalling out at stoplights. (Yes I disconnected the battery and IAC, and yes I left it idling for 5-10mins to relearn) still no codes.
Thought it might be a bad TPS, so I replaced it. (Reset new TPS) No change.
Then I went ahead and pulled the EGR valve. Full of carbon! Cleaned it out with throttle body cleaner, re-installed the old EGR valve and replaced the EGR solenoid with a new one (another forum said it would work) No change.
So here I am. The car has an unsettling idle, like it cant figure out a resting RPM, worse once its warm. It stalls occasionally at stop lights and seems to be holding back power on the initial throttle push. Once under power shes a runner! No issues at high speeds, shifts fine, and plenty of pep!
I dont mind spending money on replacing a few components if it fixes her... but I'm tired of chasing this problem and getting nowhere!
Any suggestions?
 

pcb

The Diagram Dude
:
2002 MP5
...
Now I start to get a rough idle and almost stalling out at stoplights. (Yes I disconnected the battery and IAC, and yes I left it idling for 5-10mins to relearn)
It takes longer than that.
It takes about a hundred miles of driving.
(Your 62-mile trip to work doesn't count if it doesn't go to idle during the trip)

It needs to learn how to idle at different engine temperatures, input air temperatures, and other things.

Give it some time and let it practice during different conditions.
 
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It takes longer than that.
It takes about a hundred miles of driving.
(Your 62-mile trip to work doesn't count if it doesn't go to idle during the trip)

It needs to learn how to idle at different engine temperatures, input air temperatures, and other things.

Give it some time and let it practice during different conditions.
Thanks PCB. The majority of my commute is highway driving. I'll see what it does around town. Another suggestion was to let it idle for 15mins. Do you think this a waste or is there some truth to it?
 

pcb

The Diagram Dude
:
2002 MP5
Yeah, let it idle. It needs to practice.
But you need to do it when the car is fully warmed up after your highway trip as well.

Hit the gas and then let it bring it back to idle.
Do it a bunch of times.
 
:
2003 Mazda Protege5
Sounds exactly like mine after I disconnected the battery. I would do as pcb said and give it some time.
 
Update: Took yall's advice and let it run at idle for a good 10-15mins. Then took her out for a 30min drive through town. Stoplights, traffic and lots of different idle/RPMs. Result: fixed! Car runs like new. Smooth and quiet, even with the A/C on.
Thanks again guys! Really appreciate the advice.
 
Uhmm... that's interesting.

Most all Mazda ECMs I've dealt with so far have not had a "learning mode", pretty much working off their pre-programmed parameters; the only thing they did was to retain fault codes.
The '96 - '05 MX-5 ECMS had to be run for a while [about 150 miles] just to get a couple of the monitors to show "ready" on the OBDII scanners. Other wise the performance on running of the car is the same after a battery off "reset".

I have disconnected the battery on my '19 MX-5 and did not noticed any difference in running afterwards.

OXNARD small.jpg
 
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pcb

The Diagram Dude
:
2002 MP5
I'm thinking that our car ran fine after a reset when it was brand new but after 20 years things getting worn and dirty, then it struggles to figure out the idle.


Some guys don't have trouble with the idle after a disconnect, or maybe just a few hiccups.

The service manual says to disconnect the battery to do any work on the car so it's something that happens a lot.

Your CX-5 might struggle with idle in twenty years but it's probably got smarter software.

Our car is running Windows 95. Lol
 
On a 20 YO car... the one thing that would make a car idle kinda bad and correct itself would be the O2 sensor. Any oil burning can coat them. Running the car for a while burns it off sometimes.

Reason ALL manuals say to disconnect battery is a safety issue; too many people have burned their car by "accidentally" shorting something to ground. Heck, I've seen where some instructions say to disconnect battery to change a light bulb .... ;)

And, BTW, it's NOT a CX-5.... look at the picture

I'd prefer Win95SE to Win10 anyday...:LOL:
 

pcb

The Diagram Dude
:
2002 MP5
I just can't see our car having to learn when it was brand new. That would mean that every new car would have to have miles put on it before they sell it to the customer and the mechanic would have to drive the car for at least half an hour after any work was done.
Maybe just 15 minutes at idle was enough when it was first manufactured.

There's nothing in the service manual about the re-learning after a disconnect.
All they say is to write down the radio presets so you put them back in.


There was a guy on the forum who said you should never disconnect the battery on a newer car because it messes up the ECU or something.
I posted the page from the service manual where it said to disconnect the battery before doing any work.

Oops sorry, the CX-5 was a typo.
I don't even know what a CX-5 is. Lol
I'm gonna have to google it.
 
LOL... These "computers" don't have real time clocks to "know" that they need to "learn" a new map...

That said.... the map is burned into a ROM and it's not re-writable. Only the error codes are written to a RAM, that's why removing power clears the stored codes.

The CX-5 is Mazda's USDM middle SUV. It's a very nice vehicle.
 

pcb

The Diagram Dude
:
2002 MP5
So, .. the idle info. that it "learns" must be stored in RAM then right?
Because it is forgotten when the battery is disconnected.
 
I think our ECU came equipped with a shitty idle MAP. Lol
They had to meet CAFE standards. For most '06 and up Mazda cars there is a company called Open Flash that provides you with a tablet where you can set your own parameters and then flash the ECU however you want it.
 

pcb

The Diagram Dude
:
2002 MP5
Interesting...

I know Spicy Orange used to flash our ECU's to an MP3.
You need to use premium gas after the flash and it only works for a standard transmission.
 
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