Why Idle speed can not keep up?

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Why Idle speed can not keep up?

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Mazda Forums >> Mazda Vehicles >> Mazda Protege >> Why Idle speed can not keep up?

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Why Idle speed can not keep up? - 1/6/2006 7:59:05 PM

quinto555

Posts: 17
Joined: 12/29/2005
Status: offline

I have trouble to keep the idle speed stable on my 323 protege 1990 SOHC 1800CC, I don't know if it's normal or not. Today I check the RPM with and without accessories as follow:

Idle speed with all accessories OFF = 1000RPM
Idle speed with headlight ON = 930 RPM
Idle speed with headlight and high fan ON = 880RPM
Idle speed with headlight, high fan and air conditioner ON = 650RPM

At 650RPM with all ON the engine is very rough, but If I increase to 750RPM when turn OFF all accessories the engine will rev. up to 1200RPM.

I think the ECU should keep the RPM stable as other car I have. Is the ECU gone bad? or maybe the speed sensor is bad? or maybe other sensor?

Please help.

Post #: 1

RE: Why Idle speed can not keep up? - 1/6/2006 8:16:23 PM

babyhuey

Posts: 2759
Joined: 7/28/2005
Status: offline

1000 rpm excessive for no load and the way rpm continues to drop without any compensation points to a possible fault in the idle control system. The Idle Air Control valve on the throttle body should be maintaining a relatively steady rpm. That is it's sole purpose outside of elevating idle rpm when cold. Sounds like valve may be stuck and PCM is unable to compensate for increasing loads. Might try disconnecting IAC with no loads and rerun your test. If still no changes then would definitely suspect faulty valve.

(in reply to quinto555)

Post #: 2

RE: Why Idle speed can not keep up? - 1/6/2006 8:54:03 PM

quinto555

Posts: 17
Joined: 12/29/2005
Status: offline

I know it's very fast idle, but if I set it at manufacturer spec. of 750RPM will kill the engine if turn on the air cond. Sorry I have bad english, but where is it located the Idle Air Control Valve and also what is PCM and where to find it? Thanks for your help.

(in reply to babyhuey)

Post #: 3

RE: Why Idle speed can not keep up? - 1/6/2006 9:56:03 PM

bkey71

Posts: 1469
Joined: 9/9/2005
Status: offline

The idle air control valve is located on the throttle body housing. It is probably faulty due to age or carbon build-up and needs to be removed and cleaned. The PCM (Powertrain Control Module) is the engine computer.

(in reply to quinto555)

Post #: 4

RE: Why Idle speed can not keep up? - 1/6/2006 10:11:28 PM

quinto555

Posts: 17
Joined: 12/29/2005
Status: offline

Thanks bkey71, I will try to locate the IAC valve tomorrow and let you know.

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Post #: 5

RE: Why Idle speed can not keep up? - 1/7/2006 10:58:27 AM

quinto555

Posts: 17
Joined: 12/29/2005
Status: offline

I still can't indentifier the Idle Air Control valve, I attach a picture. need help.

Thumbnail Image

Attachment (1)

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Post #: 6

RE: Why Idle speed can not keep up? - 1/7/2006 9:08:32 PM

quinto555

Posts: 17
Joined: 12/29/2005
Status: offline

I already takeoff the air intake parts, but is this the Idle Speed Control you're refering to?

Thumbnail Image

Thumbnail Image

Attachment (2)

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Post #: 7

RE: Why Idle speed can not keep up? - 1/7/2006 9:19:16 PM

bkey71

Posts: 1469
Joined: 9/9/2005
Status: offline

That is it in the bottom picture. It may be possible to clean, but more likely need replacing.

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Post #: 8

RE: Why Idle speed can not keep up? - 1/8/2006 1:56:45 PM

quinto555

Posts: 17
Joined: 12/29/2005
Status: offline

It has no ohm at all, so I pressume coil is bad as the circuit is open, have search the web for parts B55120660 but it cost $430 + freight + import tax will end up to $800, so I will try to fix it myself if can, otherwise will return it to the engine as is, and try to live with the high idle RPM.

(in reply to bkey71)

Post #: 9

RE: Why Idle speed can not keep up? - 1/9/2006 7:53:49 PM

babyhuey

Posts: 2759
Joined: 7/28/2005
Status: offline

Sounds like an internal open in the winding if you have an open circuit. Should be around 10 ohms. Dealer cost here in US is $321.75.
Have you thought about looking into a possible used parts as well. Did a little digging and there looks to be some good matches for other years that use that part #. Protege and 323 with either engine from 1990 to 1994 all use the same IAC valve. Also show the 1993 Mx3 with the 1.6l 4 cyl uses the same part. No other matches that I could find in miata, 626, mx6 etc. Might be worth a look though.

(in reply to quinto555)

Post #: 10