Truck is running rough on startup

Hey guys and gals. My 09 access cab 4x4 6 cyl is running noticeably rough to the point that I can hear a rattle that sounds like it's coming from the passenger side in the engine but only for about 2-5 minutes on startup. I live in San Diego so it's not typically cold, especially in the summer. As soon as it get a little warm - not even fully warmed up - it runs fine with no surges or anything. Could this be a dirty throttle body? I haven't cleaned the throttle body in about 3 years. Thanks!

 

Sure clean the throttle body, won't hurt to try

Is the idle super low when it runs rough? Like down around 400-500 rpms?

Any codes?

 

The idle is not low when it’s rough. It’s high since it’s right on startup. It was throwing a p0138 - high voltage at 02 circuit but I cleared it and it hasn’t come back on. I took it to get smoggiest last week and they smogged it. The p0138 code also came on 6 months ago coincidentally both times the p0138 code came on was right after I drove up the same hill on hot days, or a couple of hours after driving up the exact same hill.

 

Check for vacuum leaks around the intake.. like a torn pcv hose. Get your hands on the vacuum lines and wiggle them around

 

Maybe a chance that you potentially have a head gasket that is in the beginning stages of failure. The "running rough" maybe a misfire that is happening in the effected combustion chamber.

If it is a head gasket that's beginning to fail, the misfire occurs because enough coolant has leaked into the combustion chamber when the engine is not running over an extended amount of time. This condition prevents adequate spark to ignite the air/fuel mixture. The misfire occurs long enough until the coolant is either burned off, or pushed through the exhaust valve and into the exhaust system. The misfire can occur without setting a Engine Light. If you have a scanner that is capable of viewing Mode6 Data, the misfire will show in what cylinder the misfire is occurring in..

This is what Mode 6 Data looks like when viewing in the Torque Pro App.. you can see that my misfire is occurring in cylinder #4 because of a head gasket that is starting to fail..

 

Wow! I sure hope not. I don’t have a pro version but my reader is showing no misfires.

 

I checked for vaccum leaked. None that I can find so far.

 

Another sign of a small HG leak would be a slow drop of coolant level over time

 

I do seem to be a little low on coolant. You guys are scaring me. Maybe I should do a test?

 

Im adding approx. a cup - cup and a half worth of coolant every week - week and a half...

Does your scanner have Mode 6 data?

 

Don't panic yet just top it off and watch for a while, like a few weeks and see if it slowly goes down. Only check when the engine is cold, before starting. Check right under the rad cap

 

I don’t know. I use obd fusion app and I didn’t pay for any upgrades.

 

What do you mean under the radiator cap? Take the cap off? I can see the level on the line on the plastic Resevoir.

 

Yes, take the cap off - When engine is cold of course.
Going by the reservoir is not a good indication.

And just to make you feel better until then, it could be a leaking injector too.
Don’t worry about it just yet

 

Sorry, never done this. Take cap off and turn car on or turn car on and take cap off? Looking for bubbles, no?

 

No, leave the engine off.
Then take the cap off and see if the radiator is full.

No need to look for bubbles just yet. Not unless the radiator is low.

 

Ok, gotcha.

 

You're not looking for bubbles, just the level. Looking to see if there's any room to add coolant. Do it with the engine off and cold. This way the coolant level hasn't expanded and risen yet

The radiator is just a better place get an accurate picture of the coolant level. The expansion bottle is only reliable if the rest of the cooling system is leak free. Which we're not sure of given the symptoms

 

I park on a bit of a slope. Does that matter?

 

Ideally, you want it fairly level.
If you can not get it level. You want the front passenger side to be higher. As that is where the cap is.
If the left is side is higher, you “could” show full when it’s not. But you have to be on a pretty big slope to make a difference.

If it’s low enough, it won’t matter, you will see it.it.