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TOO-TALL
12-19-2011, 07:23 PM
Just wondering what everyone's MCX Idles at.
Last time out mine seemed to idle really low.
2003 X2

agarabaghi
12-19-2011, 07:41 PM
650 usually

sometimes if its cold or just started it goes to 750 - 770 then drops after a bit

TOO-TALL
12-19-2011, 08:18 PM
If I remimber correctly mine was at 550-600.

mikeg205
12-19-2011, 08:20 PM
mine is about 600 - but its a tbi....slight adjustment in the throttle position sensor or idle sensor thingy? Is it running smooth at 550-600? Good be a good thing on the rebuilt engine...

TOO-TALL
12-19-2011, 08:27 PM
.Yeah I 'm thinking with the larger pistons(and engine rebuild) I'll need to turn up the idle alittle bit.
No big deal I found the idle adjustment screw.

Its some what smooth...You can tell its on the edge of dieing at idle.Thats why I think its just a idle screw adjustment.

Have to wait till spring now..:( :(

JimN
12-19-2011, 08:37 PM
Just wondering what everyone's MCX Idles at.
Last time out mine seemed to idle really low.
2003 X2

What is "really low"? Post a number.

TOO-TALL
12-19-2011, 09:00 PM
If I remimber correctly mine was at 550-600....................................

Engine Nut
12-20-2011, 02:09 AM
.Yeah I 'm thinking with the larger pistons(and engine rebuild) I'll need to turn up the idle alittle bit.
No big deal I found the idle adjustment screw.

Its some what smooth...You can tell its on the edge of dieing at idle.Thats why I think its just a idle screw adjustment.

Have to wait till spring now..:( :(

There is no idle speed adjustment on an EFI engine. The idle RPM is programmed into the ECM. Should be very close to 650. There is a stop screw on the throttle body but it does not control idle RPM ... don't touch it!!!! You will mess up the air flow rate through the throttle body and mess up your IAC counts and the engine won't like it.

CantRepeat
12-20-2011, 06:59 AM
mine is about 600 - but its a tbi....slight adjustment in the throttle position sensor or idle sensor thingy? Is it running smooth at 550-600? Good be a good thing on the rebuilt engine...

The TPS does not have an adjustment on it, it's just a sensor. It measures a range of movement and sends that movement to the ECM.

The ECM is programmed with a desired idle. As engine nut pointed out, the stop is set with the IAC completed retracted. If you move the stop screw you will screw up the calibration on it.

Is the idle steady or does it fluctuate? If you cover the TB does the engine die or keep running? I'd start checking for vacuum leaks first.

TBH: I would think without some changes in the cam the stock calibration should be able to compensate for the larger pistons. The ECM will go through a learning process and adjust the VE tables using the short term and long term BLMs. I don't have DIACOM so I can't say for sure.

1redTA
12-20-2011, 07:59 AM
depending on the rebuild, sometimes... the hole in the throttle body isn't big enough for the IAC to adjust the idle speed and reaming it to a bigger diameter will help. this is the same as adjusting the blade angle to allow more air in. this works on wild cams in efi applications though, how was your rebuild??

def check for a vacuum leak and any codes

JimN
12-20-2011, 08:43 AM
...................................

I don't know what happened to my edit- I posted the question and changed it to basically the same as what EngineNut wrote but it didn't save it.

If it's not running smoothly, it has a problem and that's not an idle screw- the IAC controls idle speed. If you didn't put the ECM in diagnostic mode before you set base timing, you need to do that before anything else happens. If that doesn't correct this, check the compression/leakdown. If it's still not smooth and the spark plug wires are more than a couple of years old, change them. Ditto for the cap & rotor (I use Borg-Warner Gold because they don't have aluminum inserts and they have a lifetime warranty).

How much larger are the pistons? Any difference should be covered by the ECM- the MAP sensor will see the vacuum and based on TPS/ECT, it delivers the fuel & opens the IAC to allow 650 RPM idle.

JimN
12-20-2011, 08:51 AM
depending on the rebuild, sometimes... the hole in the throttle body isn't big enough for the IAC to adjust the idle speed and reaming it to a bigger diameter will help. this is the same as adjusting the blade angle to allow more air in. this works on wild cams in efi applications though, how was your rebuild??

def check for a vacuum leak and any codes

Rochester stopped putting a hole in the LTR throttle plate in 2000 because they made the change after the testing was done, causing a short-term issue with hot start. Once the problem was found, the recal worked fine. I don't remember hearing about the need for a recal in the other engine models. The IAC has a lot more range than needed for this application. If the throttle body needs to be reamed to allow enough idle air, I would say a different body should have been used, or the ECM program should have been changed. The LTR issue was solved by opening the IAC a bit more and I suspect the wild cam issue could have been, too.

CantRepeat
12-20-2011, 09:58 AM
I don't know what happened to my edit- I posted the question and changed it to basically the same as what EngineNut wrote but it didn't save it.

If it's not running smoothly, it has a problem and that's not an idle screw- the IAC controls idle speed. If you didn't put the ECM in diagnostic mode before you set base timing, you need to do that before anything else happens. If that doesn't correct this, check the compression/leakdown. If it's still not smooth and the spark plug wires are more than a couple of years old, change them. Ditto for the cap & rotor (I use Borg-Warner Gold because they don't have aluminum inserts and they have a lifetime warranty).

How much larger are the pistons? Any difference should be covered by the ECM- the MAP sensor will see the vacuum and based on TPS/ECT, it delivers the fuel & opens the IAC to allow 650 RPM idle.

Setting it to diagnostic mode can be done with Rinda Codemate (http://www.michiganmotorz.com/codemate-tester-mefi-code-reader-p-513.html).

mikeg205
12-20-2011, 11:11 AM
keep forgetting - I can adjust throttle on my '95 much more easily... go with the computer check Too-tall.

TOO-TALL
12-20-2011, 09:25 PM
Sounds like a trip to my dealer in the spring.

TOO-TALL
12-20-2011, 09:38 PM
There is no idle speed adjustment on an EFI engine. The idle RPM is programmed into the ECM. Should be very close to 650. There is a stop screw on the throttle body but it does not control idle RPM ... don't touch it!!!! You will mess up the air flow rate through the throttle body and mess up your IAC counts and the engine won't like it.

Good to know...thanks Engine Nut.
After reading this I'm not going to touch the stop screw on the throttle body.I'll just be patient and wait till spring to vist my MC dealer.He should beable to change the idle speed with a laptop...correct.

CantRepeat
12-21-2011, 09:28 AM
Good to know...thanks Engine Nut.
After reading this I'm not going to touch the stop screw on the throttle body.I'll just be patient and wait till spring to vist my MC dealer.He should beable to change the idle speed with a laptop...correct.

The dealer should not need to change the idle speed in the ECM* since it is already set to 650. As Jim suggested, and I overlooked, getting the timing set correctly should be your first concern.


The ECM uses a .cal (MCXMC50.CAL) file to program the ECM which is loaded into the ECM using DIACOM software (wish I had a copy and all the connectors). Changes to the .cal file require data logging and lots testing/dyno work. With the changes you have made to the motor I would bet no changes to the cal file are needed. Get your timing set and recheck the idle. Make sure you have no vacuum leaks as well.

JimN
12-21-2011, 10:20 AM
keep forgetting - I can adjust throttle on my '95 much more easily... go with the computer check Too-tall.

You shouldn't be adjusting anything on your throttle body, either. The throttle cable, maybe, but not the actual throttle plate or idle stop.

JimN
12-21-2011, 10:25 AM
Good to know...thanks Engine Nut.
After reading this I'm not going to touch the stop screw on the throttle body.I'll just be patient and wait till spring to vist my MC dealer.He should be able to change the idle speed with a laptop...correct.

There should be no reason to adjust the idle. I would look at exhaust restrictions or base timing. If you had vacuum leaks, the idle would be too high. Check for codes, especially 21 and 22 (TPS) or 33 and 34 (MAP sensor). Use the paper clip or a code scanner.