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Old 08-16-2010, 01:53 PM   #1
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Default No more idle

EDIT : problem solve, it was a boost leak, you can close this topic

Hi, I just turboed my 1990's miata

the set up is T25, 2.5" inch straigth pipe exhaust,

I run with stock ecu, stock injectors, Narrow band O2 sensor and MAF

I do have an intercooler but don't have a BOV, I need to go get a pipe that will fit with my recirc valve....

I was suppose to have 460cc injectors, 190 lph hp walbro fuel pump and LC-1 WBO2 but the megasquirt was'nt ready

so I'm running under 0 psi, I don't boost to avoid detonation until my management is done




When we first start it, I wasnt possible to reach a stabler idle, so we caped the IAC and adjust the IDLE screw, everything work fin for 2 days (saturday, sunday and this morning) (50 miles of highway and city)

but this morning when I took the exit ramp of my exit to go to work, I put it in neutral and the engine stalled, So I had to brake with my left foot while keeping a the engine at 1500 rpm with my right foot at the 3 stop I had to do.


I first try to completly unscrew the IDLE screw to compensate but it happens to be worst. (start the engine, rpm peak at 2500 rpm 2 seconds then stalled)

I screw it back, start the engine, rpm peak at 1000 rpm, 4 seconds then stalled)


My body told me to make a tiny hole in the cap, so the leak might compensate what's missing....




Hope you guys might help me!

Thanks


Marc

Last edited by absRTP; 08-16-2010 at 03:30 PM. Reason: problem solve!
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Old 08-16-2010, 02:43 PM   #2
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double posting **** - see below
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Old 08-16-2010, 02:45 PM   #3
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Uncap the idle air control valve, plumb it back into your intake line.

If your idle is still unstable, check for a vacuum leak in the intake manifold...specifically look for the plug at the rear of the intake manifold. Consider dumping a can of "Throttle body and air intake cleaner" into your idle air screw and IAC valve.

Thank you for being smart and not trying to boost on stock fuel management.
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Old 08-16-2010, 02:51 PM   #4
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My guess is that there is a leak in your intake piping or where you capped the IAC. Normally a leak would help raise idle, but since it is being sourced from the engine bay rather than being recorded by the MAF, there is extra air entering the engine that the ECU does not know about. If there is a big enough leak (i.e. a loose pipe coupler) the engine might start at first because it runs rich on cranking, but then it will stall because the mixture will be extra lean due to the excess air that the ECU does not compensate for.

Removing idle control shouldn't be a problem, as long as you don't use AC, brights, etc.
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Old 08-16-2010, 02:56 PM   #5
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Quote:
Originally Posted by fooger03 View Post
Uncap the idle air control valve, plumb it back into your intake line.

If your idle is still unstable, check for a vacuum leak in the intake manifold...specifically look for the plug at the rear of the intake manifold. Consider dumping a can of "Throttle body and air intake cleaner" into your idle air screw and IAC valve.

Thank you for being smart and not trying to boost on stock fuel management.
You can be sure that I'm going to try plumbing back the IAC the intake piping, but right now, I don't have anything with me to help me plumb these back together...

I hope I'll be able to handle my 30 miles of highway + my 4 stops to the way home....

Thanks for the advice, I'm gonna put this pipe back to the intake
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Old 08-16-2010, 02:57 PM   #6
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Quote:
Originally Posted by Cococarbine3 View Post
My guess is that there is a leak in your intake piping or where you capped the IAC. Normally a leak would help raise idle, but since it is being sourced from the engine bay rather than being recorded by the MAF, there is extra air entering the engine that the ECU does not know about. If there is a big enough leak (i.e. a loose pipe coupler) the engine might start at first because it runs rich on cranking, but then it will stall because the mixture will be extra lean due to the excess air that the ECU does not compensate for.

Removing idle control shouldn't be a problem, as long as you don't use AC, brights, etc.
don't have AC, I'm gonna go check for a leak!
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Old 08-16-2010, 03:29 PM   #7
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Oh yeah, you can close the topic!

it was a boost leak, the charge pipe was only press fitted into his bottom connector, the t-bolt clamp was'nt tight at all.

Now everything works fine


Thanks again everybody!

I'm gonna remember to always look at leaks first!
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