Really rough idle when engine is cold

[thrustn]

Every time I start the car when the engine is cold it really struggles to stay on. It dips down to around 300 RPMs and chugs for about 10 seconds then slowly increases to 900 RPMs. Today this has set off a P0101 and P0121 code but after driving the car for about an hour it went away. I have already adjusted the throttle stop screw which did help because before the car would die immediately if I did not keep it revved up for a few minutes until warm. I have already turned the throttle stop screw at least 1 full turn already which did increase the RPM on the first start-up but then it seems like the ECU takes over and corrects the RPM back to 900 RPM. Anyone else with this problem or am I just adjusting it wrong or what?

[99mx5]

Did you do the idle adjustment procedure?

1. let car warm up.

2. unplug IAC and adjust idle so that there is no change when plugged, unplugged.

3. repeat step 2 until no change when unplugging the IAC valve.

[liddown]

The IAC process is the fix...

I found that if you turn off and restart the car each time after unplugging and replugging the IAC, the process is much more effective, YMMV..... You will throw a CEL each time you unplug the IAC, just reset the code....

After getting the IAC process correct I have a perfect idle.... ;-)

[HotsideHamid]

Hmmm... I haven't heard of that process before. Is it mainly for the M2's? Or will it work on M1's as well? It seems that after I mess with the idle on my '97, the ecu finds it's own idle after a few days.

-Hamid

[Tom @ Fast Forward]

Hamid,

1. Is your IAC on the DTB at the intake manifold or elsewhere?

2. If on the DTB, do you have a check valve in the hose that comes from the MAF to the IAC?

EDIT>>>>>>

So here I am sitting at the dyno in 110F+++ heat on my PDA. :) Please ignore this post. I thought it was Hamid's hotside. The IAC adjustment will probably cure the problem.

[thrustn]

Did you do the idle adjustment procedure?

1. let car warm up.

2. unplug IAC and adjust idle so that there is no change when plugged, unplugged.

3. repeat step 2 until no change when unplugging the IAC valve.

Before I just adjusted idle screw without unplugging IAC and the computer corrected the idle back. I will do it again following these directions. Thanks

[99mx5]

I also remember jumpering 10 - GND in the diagnostic box in the engine compartment too. Im not sure if that is needed. Tom, you may have to refresh my memory. Jumpering 10 to GND in the diagnostic box will reset the ECU fuel trim tables and sets the IAC valve to the midpoint for the idle adjust process.

[Tom @ Fast Forward]

We found it works best without doing the jumper. We don't want to reset anything.

[thrustn]

Did you do the idle adjustment procedure?

1. let car warm up.

2. unplug IAC and adjust idle so that there is no change when plugged, unplugged.

3. repeat step 2 until no change when unplugging the IAC valve.

Well I followed these steps several times until my idle was around 900 rpms. But when I drove and revved the car the idle would drop to 1500 rpms and stay there about a minute before settling down to 900 - 1000 rpms. I called Tom and he told me that I should only make 1 adjustment every couple of days so the ecu can do its adjustment. Looks like I will probably need to lower the rpms but have to wait and see.

[liddown]

Is this a new coldside kit by chance, last couple of months? If yes, you might want to check your TPS adapter for clearance... I chased an issue like this also but for me it was the butterfly hanging ever so slightly open, and it would get worse with heat.. Try this next time the idle hangs.. Let it hang, open the hood and press down on the throttle hardware and see if the butterfly closes a bit...... Sorry if none of this is relevant.... ;-) Just a thought.....

[ThomS]

I also remember jumpering 10 - GND in the diagnostic box in the engine compartment too. Im not sure if that is needed. Tom, you may have to refresh my memory. Jumpering 10 to GND in the diagnostic box will reset the ECU fuel trim tables and sets the IAC valve to the midpoint for the idle adjust process.

We found it works best without doing the jumper. We don't want to reset anything.

I just got back from Pa. had a great time. Why I was out there I threw a
P0507 code, Called the Kenjistu auto and on way back Istopped in and he fixed what Mazda has said he needed to do, which was jumpering something in diagnostic box and disconnecting the battery with lights on and setting someting back to 800. Not sure what all that means. Ok done drive home, clean up the car, go for a ride and now it throws a code P0121? Any connection?

[Tom @ Fast Forward]

0507 is "Idle control system RPM higher than expected"

0121 is "TP circuit range/performance problem"

They could be related? Is your idle hanging high? Could be the idle screw is set a little high or the ECU just hasn't corrected as yet?

[ThomS]

Idle is at 500 rpm for 30 sec, later and after pushing on the gas to keep it from stalling it goes to about 1500 rpm and then after it warmed up it settles down to 800 rpm.
Put 200 miles on today and no codes. So I hope they are related.

The P0507 it seems to be happening to miatas in general even withour SC,
and more often on 02 miatas, so much so that mazda has given out instructions on how to fix the problem. But it does not happen offen enough to put out a bulletin or a recall. If the two codes are related the P0121 code happens because of the type of fix needed for 0507, I will be happy with that. Time will tell again Tom.
Thanks

[ThomS]

0507 is "Idle control system RPM higher than expected"

0121 is "TP circuit range/performance problem"

They could be related? Is your idle hanging high? Could be the idle screw is set a little high or the ECU just hasn't corrected as yet?



Don't say it Tom............................................... .........................
Today P0101 & PO121 came on today ????????X%#@&%$#@???????????
Earlier today the idle did hang high until I kicked it down.
The codes came on, not sure but I think I was above 2000 rpm.
I hope this is not starting all over. CAN NOT DEAL WITH THIS NOW.
What is my first step?

[Tom @ Fast Forward]

Do nothing. See if it happens again and if it does, does it happen when the idle hangs? If so, the idle screw might be just a touch high or there may be something causing the throttle to stick.

[ThomS]

No, the idle happened and about 1 hour later or about 55 miles later the code came on. I haven't taken the car out today yet to see if it happens again. Later . Some say you have to not go into boost at low RPM, is this true?