Low Idle (under 500 rpm)

[freewayross]

Hello All,

I have done research on this but do not have anything conclusive. My Gen 2.5 idles very low (under 500 rpm) once the engine is warmed up. So far it hasn't stalled, also the idle is smooth it doesn't jump up and down. Stays under 500 rpm.

So far I've checked Idle Air Control module using this procedure : https://www.youtube.com/watch?v=2jAgxeKTQDU

And have ruled out the Idle Air control valve, the resistance between +ve and -ve throughout the leads are over 38 ohms.

Not sure if this is related but I have the following 2 engine codes

- P0421:Warm up Catalyst Efficiency below threshold (bank 1)
- P0400 : EGR valve Malfunction

Wanted to see if anyone else has been through this and point me in right direction.

 

[earljuic3]

You either have a bad o2 sensor or your bank 1 cat is toast, my money is on the cat.

Not too familiar with P0400..

 

[Eric M]

Those two codes might be related to each other, but I don't think they'll cause the low idle.

 

[freewayross]

You either have a bad o2 sensor or your bank 1 cat is toast, my money is on the cat.

Not too familiar with P0400..

The truck has only 107k miles, can the cats be bad so soon? Can it have something to do with low idle?

 

[earljuic3]

My gen 3 has 130k and both cats just went bad in the last 6 months


Sent from my iPhone using Tapatalk

 

[Howah]

Have you tried adjusting the idle screw on the throttle body?
Leaking egr valve would cause a low idle as well.

 

[dieseltechJay]

Have you tried adjusting the idle screw on the throttle body?
Leaking egr valve would cause a low idle as well.

I wouldn't go messing with the idle screw without eliminating other culprits first. It's set from the factory. On turbo Mitsu's low idle was usually a vacuum issue. I'd check for a vacuum leak at the EGR first. That may even fix your cat efficiency issue as well. If the EGR isn't directing exhaust gases back through the system and isn't doing it's job the O2 sensor is going to see the exhaust being dirtier than it should be after warm up.

 

[Salonika]

I agree with Jay, go through the EGR system first. Your Manifold Differential Pressure Sensor keeps an eye on the EGR as far as I know. When the ECM commands the EGR to activate, the MDPS looks for a pressure change inside the manifold. If it isn't happy, it might set the P0400. If your EGR is leaking some exhaust gas that could cause your low idle, but it also could mean the EGR isn't working right when it is commanded to open, and I'd guess that's when your codes are thrown.

 

[freewayross]

Thank you guys from what I've tested so far, I think EGR valve is the culprit too. When I pinch/choke the vacuum line as shown in the below video, the truck doesn't die. So i think EGR is the problem. Is there another test to rule out the EGR solenoid? Would hate to replace it and find out otherwise.

https://www.youtube.com/watch?v=2jAgxeKTQDU

 

[dieseltechJay]

A vacuum pump is the best way to check if it works or not. If you don't have one just drive the a local auto parts store that rents specialty tools (O'Reilly, Napa) and borrow one. I think they'll be happy to sell you an EGR in exchange.