Rough idle after initial warm up

[samert111]

Working on a 2005 Legacy GT, 2.5L Turbo and at cold start up it idles great at around 1500 RPM for about 30 seconds then as soon as it tried to idle down it's like a switch is thrown and it starts to idle rough and will also stall sometimes. Each restart once it's warmed up the idle is rough but let it cool completely and the cycle starts all over. It's obvious it's running too rich once it starts to stumble. Car runs great while driving it as long as you keep the RPM's up.

 

The PO removed the Cat and replaced it with a wrapped down pipe from the turbo. The O2 sensors appear to be operating correctly per my scan tool. I'm also getting misc cylinder misfires on all cylinders which make sense because it's over fueling. The MAP sensor seems to be working and showing different readings at various stages of throttle application. When I connect my vacuum pump to the MAP to raise and lower the vacuum applied to it at idle it doesn't affect the idle condition at all so I'm not sure what to make of it. Maybe we have a bad ECU.

 

I've cleaned the throttle body which wasn't too dirty at all and looked all over for a loose or damaged vacuum hose. I've pretty much drowned the intake manifold and all vacuum hose connections with carb cleaner and I'm not getting any fluctuation in idle at all so I think all the hoses are intact.

 

I'm stumped and any suggestions would be appreciated .

[relative4]

What do your fuel trims look like? How many misfires are you getting at various RPM levels?

[MilesA]

Usual suspects are vacuum leak, PCV valve, turbo inlet, throttle body, idle air control valve, MAF sensor. Sounds like you have checked out some of this already.

 

Some of the vacuum lines can't be accessed until you remove the intercooler. There is a blue plastic tee that connects several vacuum lines under there. These lines can pop off and lead to problems similar to yours.

 

If you have the intercooler off, this is a good time to check the PCV.

 

Also, you should check the turbo inlet pipe. These can split and crack on older cars, typically where the inlet pipe connects to the turbo.

 

You may want to clean the de-gunk the idle air control valve.

 

MAF sensor is easy to clean. Don't use carb cleaner, that will damage it. Use a special alcohol-based spray cleaner for this.

[samert111]

What do your fuel trims look like? How many misfires are you getting at various RPM levels?

 

Full disclosure, I'm not real good at diagnosing these fuel and sensor related issues unless my scanner can point me in the right direction with a code and that's the problem here is there are not any codes related to O2 , MAF or MAP sensors to steer me in the right direction just the random cylinder misfires and I refuse to just start throwing parts at cars to hopefully pick the right one. If you need a Cadillac Northstar engine rebuilt complete with the block drilled and tapped to accept head studs then I'm your guy.

 

Anyway to answer your question, following are a couple pics of the fuel trim readings from my scanner. First one is at 1500 RPM and the 2nd is at 2500 RPM and the last one is the O2 sensor readings.

 

As far as how many misfires each cylinder had, my scanner doesn't support that. Just that there are misfires.

 

The thing about this morning when I first started it up cold it did not run smooth for the 1st 30 seconds or so like it has been, it started out missing right away.

[samert111]

Usual suspects are vacuum leak, PCV valve, turbo inlet, throttle body, idle air control valve, MAF sensor. Sounds like you have checked out some of this already.

 

Some of the vacuum lines can't be accessed until you remove the intercooler. There is a blue plastic tee that connects several vacuum lines under there. These lines can pop off and lead to problems similar to yours.

 

If you have the intercooler off, this is a good time to check the PCV.

 

Also, you should check the turbo inlet pipe. These can split and crack on older cars, typically where the inlet pipe connects to the turbo.

 

You may want to clean the de-gunk the idle air control valve.

 

MAF sensor is easy to clean. Don't use carb cleaner, that will damage it. Use a special alcohol-based spray cleaner for this.

 

Yep, I've check all this already with the exception of the IAC which it doesn't have one, It's ETC.

[samert111]

OK, so here's some more info on this issue. I'm a firm believer in finding out what if anything has been done on a car just prior to having a problem. So I called the owner and he told me that just 15 miles prior to having this issue he put a can of O'reilly Auto's injector cleaner in a full tank of gas then drove it 15 miles home and went out later to go to work and that's when this rough idle issue first started.

 

I've personally never used an injector cleaner in a can product but just wondering if this stuff could have loosened up a bunch of crap and plugged up the injector filters since this car doesn't have a replaceable fuel filter other than the one in the tank.

 

Have any of you guys ever had or heard of this stuff causing problems with the injector filters on these engines?

[Max Capacity]

Dose the car have the large orange o-rings between the TGV's and intake manifold. if not replace the small black ones with the orange ones.

 

Common issue when its cold out.

[samert111]

Dose the car have the large orange o-rings between the TGV's and intake manifold. if not replace the small black ones with the orange ones.

 

Common issue when its cold out.

 

They are orange.

 

Strangely enough the more I run this car the better it's starting to idle. So I gave it back to the guy and told him run the car for a few days and keep topping of the tank with fresh good quality fuel to run out the injector cleaner.