Weird Idle when stopped at a light

[phoenixrage]

This is happening in my 05 3sport GT - 5spd.

When I come to a stop at a light, the engine will struggle to idle for a few seconds before stabilizing and idle fine. It'll dip to probably below 500rpm, and speeds up to 1000rpm, it does this probably 3-5 times.

[Donutz]

Have you reset your ECU recently? What accessories do you have on when that happens? I know I drop down to 500 rpm after I reset my ecu, but once it relearns it holds steady around 700 - 750. Also, when I'm running different accessories, it tends to run at different RPM.

[phoenixrage]

nope, completely stock, playing radio.. and thats it.

[Flagrum_3]

Could be a number of things; Dirty sensors, dirty throttle body, bad gas, bad oxygen sensor etc; etc;

Simple thing to try is disconnect your battery for 20 minutes or so get some Fuel system cleaner fill the tank with fresh gas and see if it goes away....if not maybe have it scanned or have the throttle body and injectors flushed properly.....just a few thoughts!


_3

[sas]

I completely agree with Flagrum. Can to add leakage in manifolds and faulty IAC valve.
This behavior means that your engine can't to work in "closed loop" mode and switching to "open loop".
There is a "puzzle". Why short fuel trim is changing or long trim is not corrected?
Mazda has the quite reliable checking algorithm for sensors, and most errors
are revealing after second full drive cycle (Start -Open loop - Closed loop - Stop).
Best you can do is, to give engine to work before switching off, about 1 minute.
If in the second time you not have CEL and this behaviour continue, reset PCM.
The 20 min. is looking bit long. I pushed break pedal on 10sec. and then
waited 2-3 min. After reset you must to learn computer - warm engine and drive 20-30min at different speeds without acceleration and load,then switch off the engine.

[phoenixrage]

yea.. its not giving any CEL at all.. it just does it for a few seconds, and eventually it stablilizes and is normal.

I'm going to try a fuel system cleaner later.. since I just bought the car, It may have been sitting for a while before then.

[Flagrum_3]

yea.. its not giving any CEL at all.. it just does it for a few seconds, and eventually it stablilizes and is normal.

I'm going to try a fuel system cleaner later.. since I just bought the car, It may have been sitting for a while before then.

It's an '05 right? What's the mileage on her? If your at high mileage a Fuel system cleansing at the dealer might be needed!...If your going to use fuel system cleaner try Redline and use the full bottle! I would also suggest not getting fuel from the same station as last time...find a busy station in your area and fill there, then take it to the nearest hiway and redline it thru the gears to clean her out, then see if the idle steadies.


_3

[sas]

If, there is static influence you must have CEL (something similar to “bank too lean” or "bank too rich" ).
Do restore computer and if this not help do diagnostic.
Without CEL ordinal error scanning can’t to help.

[phoenixrage]

It's an '05 right? What's the mileage on her? If your at high mileage a Fuel system cleansing at the dealer might be needed!...If your going to use fuel system cleaner try Redline and use the full bottle! I would also suggest not getting fuel from the same station as last time...find a busy station in your area and fill there, then take it to the nearest hiway and redline it thru the gears to clean her out, then see if the idle steadies.


_3

yea i was thinking the same thing. My 05 is low km's... just hit 35k on it. So it may not have been pushed by the previous owner.

[mazda lover]

yea i was thinking the same thing. My 05 is low km's... just hit 35k on it. So it may not have been pushed by the previous owner.

maybe the speedo was turned back? where did you buy the car? private or dealer

[Walrus]

maybe the speedo was turned back? where did you buy the car? private or dealer

Digital odometer?

[sas]

It could be the temporary failure.
The previous owner had his own habits in driving.
Possible, the car stood long time and sensors changed their characteristics
or corrections in map is not compatible with this weather .

[phoenixrage]

i got it from a pontiac dealership.

[phoenixrage]

so, i put in some fuel system cleaner.. so lets see if it helps, so far its still happening with the new tank of ultra94.

but to further add, once the idle stabilizes (while im stopped), if i rev the engine, it'll go back to idling fine w/o the problem. It only happens if I drive some distance and come to a stop. After I stop a while it doesn't happen again till car gets moving.

[sas]

I hope you used cleaner in right ratio as written on bottle. Usually, the whole bottle on tank. You can to clean your air filter too. Pay attention, what going behind the filter (dirt, oil, moisture) and condition of filter.

[phoenixrage]

yea.. i'll pop the hood to check out the airbox... yea the bottle said just use the whole bottle.. treats UP TO 75L tank. or something like that..

[phoenixrage]

well, didn't get a chance to pop the hood to check the airbox.. but the weird idle is gone now, so hopefully it stays that way.

But is this normal? right when I let off now, it idles at around 850-900.. then after a couple seconds, it'll drop back down to 700ish.

[Flagrum_3]

well, didn't get a chance to pop the hood to check the airbox.. but the weird idle is gone now, so hopefully it stays that way.

But is this normal? right when I let off now, it idles at around 850-900.. then after a couple seconds, it'll drop back down to 700ish.

That's what mine has done since new, so I would say yes it's normal.


_3

[sas]

When you are dropping accelerator, the fuel cut mode is enabling.
At 1200 rpm is enabling mapped mode (revs are dropping at 850rpm) and 1.5-3 sec to adjust trim(1-2 revolutions of oxygen sensor). This sounds normal.

[phoenixrage]

thanks everyone.

[CanSpeed 3]

Thats a sympton of a fualty perge valve. Mine did that. Dont be surprised to see a cel soon.