another idle q

[mazdasport]

hi guys
me again, just want to say thanks to all the guys for their
help so far, as a result i have been able to fix many of the small
iritating faults on my ba.
she's running nice and smooth and responsive now.

Just one thing I cannot for the life of me figure out
its nothing really drastic, but just annoys me

As of lately, after cleaning and checking everything is working
well. i just cant seem to get her to idle at 750ish without having
the idle air screw closed completely, as soon as i loosen it
just abit, it starts to pick up the idle
so now i usually idle at around 1000rpm.
any idea/clue why this could be?
Iv tried the GND TEN method many times
Iv adjusted the TPS to 0.49v
Iv cleaned the MAF
Iv cleaned the IAC (which completely fixed the idle dip problem, when
you brake)
Iv checked for vacuum leaks
so im just abit stumped?
Should I reset the Ecu?
will that make any diff?

[Clean_Cookie]

worth a try resetting the ECU but i have no idea either. what about the timing?

[Cosmo Dude]

A/C off?
Rear demist off?
P/S pressure switch working as per manual? (no I cbf looking at my manual)
Auto/manual
Anything that uses excesive current or engine power will cause the idle to increase.

Forums work best when members, like you, give back information not just ask questions.

[Clean_Cookie]

at least hes trying and asking more complex questiins than "what will make my car go fast without spending much $$$...

personally i think its valid.

[mazdasport]

@cosmodude> sorry man,
its a manual so its in neutral
and nothing i could think of could be using the power.
radio is off, ac off, lights off.

[mazdasport]

@tc#racer> thanks for the support man,
yeah you see im trying to get it running a 100% or the nearest possble atleast
iv got it for 3.5years now, have been learning alot about the car
and am tired of mechanics just saying oh its an old car, you cant get everything right.

and when you say timing? are you talking about the ignition timing? or the cam timing?
car isnt realy pinging or anything, cambelt timing is right, was checked a week ago
Correct me if im wrong, all that the idle air screw does is control the idle right?
and when you set the base idle that too only controls the idle?
so that said, it shouldnt really be prob if i have my idle air screw just a turn or so away from being closed? (almost closed) this shouldnt affect performance or anything of that sort right?
and iv checked, if i switch the lights on at idle or turn the powersteering,
the idle will go up just a bit for a second or two and come back to 1000rpm.
so im sure the IAC valve must be working

[NaughtyGT]

After reading a 2nd time. I'm not sure on the TPS adjustability method? I'd put money on shagged TPS? The V6 MX6's tend to idle high & rev up & down erratically when there stuffed. May be worth simply replacing. Also, if you disconnect them, the erratic revving stops but it will stay idling high. Better in the meantime than the up/down revving. Drove me mad.

[Clean_Cookie]

mines rooted, do you get one from mazda or aftermarkdt?

[mazdasport]

@naughtygt>ok thats worth a shot i guess
so youre basically saying that even though when i adjust the TPS and the voltage is changing accordingly, it could still could be the cause of the crazy idle?
hmm..now where to get another one to try on before buying

[NaughtyGT]

it's a bit difficult to be sure without testing I'm afraid

[asanga]

Originally Posted by mazdasport

@naughtygt>ok thats worth a shot i guess
so youre basically saying that even though when i adjust the TPS and the voltage is changing accordingly, it could still could be the cause of the crazy idle?
hmm..now where to get another one to try on before buying

If you test your TPS as I mentioned in your other post and there are no voltage spikes within the full range of the TPS then your TPS is ok. there are other things affect the idle. if your coolant temperature sensor is faulty (i.e wrong resistance even after engine is fully warmed up) then the ECU will run the engine at higher RPM. also if your Idle control valve is faulty ( not closing completely you'll have high idle as well. There are many factors that affect the idle and you have to rule one at a time. Also when you set your base idle did you put the ecu into diagnostic mode (short TEN to GND) , you must never adjust your idle screw without shorting TEN to GND , otherwise your ecu will try to compensate every time you change ur idle (like chasing the tail). when you set your base idle you should set your base ignition timing as well, its important to get your base settings right. also an error code check can point out possible faulty sensors.

[mazdasport]

@asanga, ok you right there, let me start checking each one over again, and rule out each possibility,
coolant temp sensor is new, so im sure thats still good
i will check again for spikes with the TPS today when I get home
Please correct me if im thinking wrong here. I have my TPS set at 0.47
at closed throttle, so Im assuming what you are saying is that the reading
should stay constant at 0.47 throughout the range as i open the throttle?
correct?
when it comes to IAC Valve, im sure its working, but cannot guarantee its opening and
closing full.
is there any method of me checking that? without removing it from the TB again?
like using a mulitimeter or something?

[mazdasport]

@all other users, please bear with me as i keep updating this thread, as i eliminate all possibilities

[asanga]

Originally Posted by mazdasport

@asanga, ok you right there, let me start checking each one over again, and rule out each possibility,
coolant temp sensor is new, so im sure thats still good
i will check again for spikes with the TPS today when I get home
Please correct me if im thinking wrong here. I have my TPS set at 0.47
at closed throttle, so Im assuming what you are saying is that the reading
should stay constant at 0.47 throughout the range as i open the throttle?
correct?
when it comes to IAC Valve, im sure its working, but cannot guarantee its opening and
closing full.
is there any method of me checking that? without removing it from the TB again?
like using a mulitimeter or something?

when you open the throttle slowly at a constant rate the voltage should increase proportionally. The wide open throttle voltage should be within 2.8v-4.5v.

IAC can be checked with a multimeter , it should read about 11-12 ohms between the terminals. pic below is for series 1/2 , not sure what urs is but similar concept except series 3 has internal air path for IAC where as series1/2 has external path from intake air hose.

[mazdasport]

thanks asanga, thats some usefull info, will work on it this weekend and keep you updated on my progress.

[maztech]

Sounds like the IAC valve is buggered not working to full duty cycle . You have a air leak past the throttle butterfly causing the high idle . Also spray heaps of water around inlet gasket to make sure the gasket has not perished

[mazdasport]

ok update and q here,
Firstly like you guys predicted, the IAC has had its days. cant even get a proper resistance reading of it. Once I unplugged the IAC connector plug with removing any of the vacuum pipes, and presto....the idle sits perfectly smooth at 750rpm. no vibration nothing...perfect, but connect it back on again and then the car is idling at 1400-1500-1600 almost all the time, fluctuates between that range, cold start is worse and fuel consumption is gone throught the roof. off 20l of gas this week, i got around 150kms with mainly highway driving. So i think its definitely time to change the IAC unit.
Q> Do I have to replace the whole unit? or is there only a valve or something that I should change?
Do you still get the whole IAC unit new at any stores?
And lastly, for the interim. can I drive around with the IAC connector plug disconnected?
(will it cause any harm, except for the dip in idle when stopping etc?)
THis is urgent info that I need pls guys.
Thanks for all the help again.

[maztech]

Replace iac just by itself
Either from wreckers or new
Won't do much other than unstable idle or low idle when throttle snaps closed tune it out with air bypass screw and it wont adjust idle when ac Power steer or elec loads are needed