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Old 15-10-2018
ShaneWJ  ShaneWJ is offline
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Default Surge with AC on

Hi,

I got rid of the idle surge in park and in drive with foot on the brake by cleaning the intake temp sensor.

Now I noticed with the AC on its way worse! Idle with AC bounces between 500-1500 rpm. Blows black smoke as it bounces almost with a rhythm to it.
Turn the AC off and disappears instantly.

Obviously some kind of load causing over compensation of idle by the computer?

Any thoughts or experience or remedies?

Thanks

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Old 15-10-2018
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Any codes?
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Old 15-10-2018
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No codes at all...
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Old 16-10-2018
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Usually a faulty injector will cause surging like that.
Been there, done that, if I would wait long enough idling in drive, the car would start to pulse when easing off the brakes. Faint pulsing, but it was there.

You can do a leak-off check to confirm if it's an injector at fault.
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Old 29-10-2018
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Hard to believe its an injector.

The only time it surges is when the AC is on, stopped in drive. And when the engine temp is below 70 degrees. Once it warms up over that it disappears completely.
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Old 29-10-2018
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Why do you find it hard to believe it's an injector?
At idle the ECU compensates the extra load by injecting more fuel and it's tiny quantities, if an injector is worn out it's difficult to control small changes in injection quantity.

Leak-off test is easy and simple, you need some 3mm hose, 5 bottles and 30 minutes of time.

If you have the ELM327 adapter and JeepDiagPro you can also look at injector correction values.
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Old 29-10-2018
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Injector would show more consistent signs in my eyes?

Not ruling it out or your advice its just odd it only happens under one condition. No starting issues or poor fuel economy.

I do have elm327 and diagpro. What conditions do I compare the values? Ac vs no ac?

Thanks
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Old 30-10-2018
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Look at correction values A/C versus non A/C, in Drive and in Neutral, cold vs warm.
Start first with the setup that causes the bad idle and also poke around and explore other conditions.

If all injectors are less than +/-3, then move on to actual rail pressure vs desired rail pressure to see if the pressure regulator might be behind it.

We've had a recent topic of a guy from Italy which also had symptoms that did not seem very consistent, turned out to be a cracked injector.
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Old 3 Weeks Ago
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Start with injector 4? Sigh...

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