Engine idles rough and dies at idle.

[Jimmy John]

This used 2004 Suburban 5.3L Z engine has increased my knowledge considerably in the last week with all it's issues. The latest is a rough idle and stalling at idle. This happened for the first time the day after I brought it home. I was like great it didn't do that when I bought it. Today it did it again but I believe I found a common link between them. The first day I brought home the Burb I could not get the key to come out of the ignition so I gave up and just let it set overnight. (In case you experience this issue I discovered that If I did not get the gear shift lever to read Park the key would not release also it ran the battery down apparently it leaves a lot of power on) The next day the battery was completely dead and I took it out and charged it the next day. When I put it back and started up the engine it had all this rough idle and stalling at idle engine issues. I drove around the block but it kept stalling and would not stay running long at idle. Next day it was like it never happened it seemed to run fine and had been for over a week now until this morning. I did however unhook the battery last night to remove the Washer fluid reservoir because it had a leak. The battery was disconnected for probably 3 hours. So you probably see where the pattern is if I disconnect the battery I get the Engine idles rough and dies at idle issue so I'm thinking later today it may run fine again. I also have one engine code that appears P0449 although there was no code today after the battery had been disconnected. Just wondering if this code could be linked to the Engine idles rough and dies at idle issue?

 

[BIGGERSHAFT94]

Your computer has a basic idle speed setting for when the vehicle is new. As it gets old the deposits in the throttle body build up and the computer compensates for those deposits by letting more air in at idle. The older it gets, the more substantial the compensation is. When you disconnect the battery for more than a minute or two it forgets to compensate for the deposits and you have to do an idle re-learn. So there is 2 ways to fix this problem.
1: remove and clean the throttle body with some brake clean and a shop towel.
2: idle re-learn. To do this hold the throttle at about 1000 rpm until it warms up with all accesories (lights radio ac etc..) off. Then let it idle on its own for a minute or so (may take a couple times of feathering the throttle to get it to idle good). Next just put it in drive with your foot on the brake. After about a minute or so turn on all the accessories with the ac on full blast. This should fix your problem.

Edit: if you choose to clean the throttle body you may still need to do a idle re-learn.. also before you do a realearn let it sit with the battery disconnected for about 10min. The shifter spring in my 01 is the same way, you just have to make sure you push the shifter back to release the key

 

[06Escalade]

Check this video out

 

[Jimmy John]

Did some more research. Drove home from work and it still ran bad. Hooked my fuel pressure gauge up the next day and I take the schrader valve out first because I just use a hose with a gauge on the end of my homemade pressure gauge. Anyway no fuel at all leaked out when I removed the valve and I found that strange? After hooking the gauge up it started up and ran fine again. Then drove in town and after 3 miles started running bad again. This time I noticed the pressure seemed to not move anymore when I accelerate as it normally goes up about 4 to 5 psi when I first accelerate. Stopped and disconnected the fuel pressure regulator vacuum line and pressure moved up some and it ran fine back home 3 miles. When I got home I reconnected the vacuum line and it idled fine once again. Disconnected battery again for an hour or so and made sure the engine light was off when I restarted it so I knew the code was cleared and it ran a little rough at first but didn't stall this time so I'm beginning to think that just unhooking the battery is not the cause of my stalling problem and is more likely fuel related.

Key on pressure engine off 52 psi
Key off engine off 48 psi.
Engine running 42
Engine acceleration jumps to 45 for a second and drops back to 42.

When it started running rough the pressure was a steady 39 psi and acceleration made no difference it just stayed glued on that number until I stopped and un hooked the regulator vacuum line.

 

[Jimmy John]

Does anyone know what the minimum pressure needs to be to keep the engine running or when you would most likely start to see symptoms of a low fuel pressure issue?

 

[Jimmy John]

Was looking around underneath it yesterday and found the bottom hose nipple is broke off of my vapor canister. Most likely this is the cause of the p0449 code and the loose gas cap warning. Any ideas on how to repair that issue outside of buying a new one?

 

[Jimmy John]

New update: Replaced the intermediate steering shaft and bearing at the end of the steering column which did get rid of all the clunking feeling and sounds in my steering. While I worked on this I unhooked the battery over night while I finished the job the next evening and when I tried it out the next day bingo the rough idle and dies at idle problem returned. I drove about 5 miles from about 30 mph to half on the highway about 65 mph. Stopped in a parking lot and the engine died. Unhooked the fuel pressure regulator vacuum line and was getting the full 52 psi and still the engine would not idle so I think I can rule out fuel pressure and I also had just changed the fuel filter a few days earlier . Drove it back home and by the time I got back I had no more idle issues. I think its pretty safe to say now my problem is related to unhooking the battery for over 24 hrs. Not sure what it is causing but either the idle air control valve is sticking while recalibrating by the computer or its just the computer recalibrating out of a range that would keep the engine rpms high enough to keep it running. I would like to try unhooking the battery over night one more time just to see what happens.

 

[Yukon2000xl]

New update: Replaced the intermediate steering shaft and bearing at the end of the steering column which did get rid of all the clunking feeling and sounds in my steering. While I worked on this I unhooked the battery over night while I finished the job the next evening and when I tried it out the next day bingo the rough idle and dies at idle problem returned. I drove about 5 miles from about 30 mph to half on the highway about 65 mph. Stopped in a parking lot and the engine died. Unhooked the fuel pressure regulator vacuum line and was getting the full 52 psi and still the engine would not idle so I think I can rule out fuel pressure and I also had just changed the fuel filter a few days earlier . Drove it back home and by the time I got back I had no more idle issues. I think its pretty safe to say now my problem is related to unhooking the battery for over 24 hrs. Not sure what it is causing but either the idle air control valve is sticking while recalibrating by the computer or its just the computer recalibrating out of a range that would keep the engine rpms high enough to keep it running. I would like to try unhooking the battery over night one more time just to see what happens.

Mine does exactly the same thing I just stopped unhooking the battery truck runs fine


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