Rough LS1 idle

[anvlson1]

I had a look through the forums but could find anything that helped....
Basicly my car in the last few days has developed a really rough idle to the point were the car almost stalls. Its a 5.7ltr Vx with a maffless tune. Ive got no idea whats doing it, the only thing i though it could of been was if it was sucking up water through my cold air intake when i go through puddles (as it pokes out the bottom of front gaurd) but that wasnt it.
Any help?
Cheers

 

[soop]

I've had a similar issue, but its been kind of random in its occurance.
I'm waiting for a scan tool to arrive so i can check and see whats causing it, but im betting on a crank angle sensor though.

 

[SSINZ]

the issue is either the leads or quite possibly the spark plugs. its a common thing. change ur spark plugs if that dont work change your leads. it wont matter to much as u prob need these 2 new parts anywho so save yourself some money for next service. and they arent to expensive either.

 

[Red Ute]

I had a look through the forums but could find anything that helped....
Basicly my car in the last few days has developed a really rough idle to the point were the car almost stalls. Its a 5.7ltr Vx with a maffless tune. Ive got no idea whats doing it, the only thing i though it could of been was if it was sucking up water through my cold air intake when i go through puddles (as it pokes out the bottom of front gaurd) but that wasnt it.
Any help?
Cheers

My LS1 VU ute idles rough when cold. O2 sensors new, oil pressure sensor new, vacuum hoses under engine cover as new. Injectors replaced in 2017. Engine light comes on intermittently but goes out before I can get tested for the code. What could it be?

 

[slipknot09]

When is the last time you cleaned the MAF and throttle body? Like most cars it needs a clean every few years. You mention only when cold indicating it could be the IAC. Does your car idle high when cold though? It should if the tune is factory to prevent stalling.
My car seems to idle noticeably rougher when I fill up at a certain
7-11 that’s on my way to work. It’s not the placebo effect either I’ve tested many times. I even asked the Sheila working there if complaints were common and she said no one ever has

 

[slipknot09]

Also 90% of the time I get an engine light is due to low oil or oil pressure sender. But I do a lot of km for work and often travel 10-15k between changes.
Do you have a OBD app? If so here’s 2 PIDS to monitor what your IAC is doing, if the numbers don’t match or the actual IAC position lags behind desired IAC position by more than a second it could be gummed up. Another sign of a failed IAC is if you don’t hear the IAC valve make a noise every time you turn the ignition off, it’s the last thing the PCM does before shutdown

"Name"	"ShortName"	"ModeAndPID"	"Equation"	"Min Value"	"Max Value"	"Units"	"Header"	"Priority"	"Scale"
Actual IAC Position	IAC Pos	22117201	((A*256)+B)/2	0	255	steps	Auto	High	1
Desired IAC Position	Des IAC	2212F701	A	0	255	steps	Auto	High	1

 

[Aus78Formula]

12 years on, he has been patiently putting up with the problem, until this thread dig.

 

[krusing]

Could be a vac leak,

Get it smoke tested,
That should show up any faulty components.

 

[Red Ute]

When is the last time you cleaned the MAF and throttle body? Like most cars it needs a clean every few years. You mention only when cold indicating it could be the IAC. Does your car idle high when cold though? It should if the tune is factory to prevent stalling.
My car seems to idle noticeably rougher when I fill up at a certain
7-11 that’s on my way to work. It’s not the placebo effect either I’ve tested many times. I even asked the Sheila working there if complaints were common and she said no one ever has

I haven't cleaned the MAF - will do, thanks. If it doesn't fix the issue I'll replace the temperature sensor. Pity the engine light doesn't stay on.

 

[slipknot09]

You can easily test your temp sensor thru the “engineering mode” in your cluster. Hold the mode and set buttons on your mode switch while starting the car or while turning key on ON, use the arrows to scroll to coolant. It should start around ambient temp obviously and climb to around 80 within ten mins. Hit 90 if sitting in traffic and 100 is possible during summer but is pretty hot.
Just buy a cheap OBD2 adaptor, they’re available everywhere online. I personally only buy OBDLink ones but Chinese ones can work just as well.
Even if the engine light is intermittent it will be stored in the PCM under history codes