Please Help 1999 Silverado!!!!

I have a 1999 Silverado Z71 Ext Cab. 113,000 miles. After it sits overnight, I start it and it idles really bad like it is going to die, but it doesn't. If I let it run for about 5-8 minutes it is fine all day. If I don't let it sit for awhile, then when I put it in drive it lags and sputters for a second or two and then it is fine all day. Fuel filter, air filter, PCV valve and spark plugs have been replaced. All 9 computer updates have been applied. Fuel pressure regulator tested fine as well. Fuel pump doesn't whine or show any signs of failure. There are also no codes showing in the message center, and no codes show up when GM tech hooks up diagnostics to it. What could be the problem???

Hey Mulaka Which 9 Computer Updates Are You Talking About. I Never Received Any Notices On This. I Have A 99 Silverado Ext. Cab. With 113,659 Miles.

I agree with powerdrill, I think some mechanic´s been charging you for something that he hasn´t done, but anyway, the sputters or noises you hear could be piston slap, I have seen many posting wher the vortec engine is experiencing this and that even GM has bought back some trucks. GM doesn´t know what it is and our engines may be doomed to a shorter life because of this.

No, they are ligitamate updates. Go to the Chevy dealer and ask them to run your VIN number to see if any of the updates have been applied to your truck (if it is used), if you are a one owner you should know. They hook up to the truck and put them into your computer. They printed off the codes for me to explain what each one was for. There was one for a the transmission shifting hard, one for driveability concerns such as rough idle etc. It only cost $47.00 to do it. I don't have any kind of piston slap or noise or knock. Just the cold start rough idle (sometimes) and then when you put it in drive it doesn't respond right away(1-2 seconds) then it sputters on and is fine until the next morning cold start.

Bump. Come on guys....help!

Have you tried different fuel additives? Maybe run a higher octane or even add some Fuel injector Cleaner?

No, I haven't tried those. What do you recommend?

What octane fuel are you using? You should be using regular 87 octane..using a higher octane could cause some cold driveability issues.
Is this the old body style or the new body style? Since you say Silverado, I'm going to assume this is the new body style with the 5.3 or 4.8 engine.
First I would look at the condition of the throttle body..a good cleaning may help.
Next I would check fuel pressure..is it bleeding down or slow to build on start-up.
Next I would check the sensor data to the PCM..you may have a sensor (CTS, MAP) that is a little schewed causing your concern.

Hey Mulaka Which 9 Computer Updates Are You Talking About. I Never Received Any Notices On This. I Have A 99 Silverado Ext. Cab. With 113,659 Miles.


You will not recieve notices of calibration changes.
These changes were made to address concerns on these vehicles that could be fixed by a change in software calibrations..usually these changes are referenced in a TSB from GM.

I use the regular grade gas..nothing higher because the owners manual says no too. Fuel pressure is good...strong. Haven't checked the throttle body yet. Where is it and how do I clean it?

I run 91 Octane in my 5.3 L and it seems to like it. I've used STP Fuel Injector cleaner in the past and I've noticed an increase in power, starting, and smoothness afterwards.

What oil are yuo using?

I use Mobile 1 5W 30

If you want to know about your vehicles calibration go here http://calid.gm.com/vci/VINEntryPre.do

Since doing the computer updates, the idle is normal now. When I put it in drive though, I still get a quick 1-2 second stall and then it goes fine. Would a good dose of STP Fuel Injector Cleaner maybe fix this? Read the very first post to see what all I have done so far.

Drop some b12 chemtool in your tank. You can get it at walmart and it comes in a metal container. If that doesn't clean your fuel system then you probably need to have your injectors professionally cleaned. I also remember the guys in the service dept talking about a problem with water entering the fuel system from the breather under the bed that allowed for rust to form in the fuel system that caused problems for some people but I can't remember if it was limited to the 99's.

I have tried all the advice everyone has given me...but no change. The rough idle comes and goes, but once it warms up...2-3 minutes it goes away. The 1-2 second putter when I first take off in drive on a cold start is still there. Anyone have any ideas?

Check the screw that holds the distributor cap in place, is it loose, broken??

I am not an idiot...really, but where exactly is the distributor cap located on a 5.3 V8?

I have a 5 speed stickand when i start it cold and do not goose the engine up above a thousand rpm it will stumble the first time i let the clutch out and pull out of my parking space. As long as i goose it once or twice before i put it in gear it is fine. Im guessing that when the throttle bodyis closed all nite it is sticky that first time you touch the peddle. Also, i run a tank of 93 octain and a double dose(in one tank of fuel) of injector cleaner about every three months, i get huge performence gain after a half of a tank and it does fine for several months. When it starts to get slightly sluggish i do it again. JJ

On my 5.7L V8 it is in the middle of the engine right up to the firewall, has one wire coming from the ignition coil and from there go out the spark plug wires, I think my engine is set up more like the V6 than a V8, so it may be different.

Sounds like it could be your fuel pressure regulator. Easy to check and easy to fix (you can do it yourself). Located about midway above the left valve cover, has a vacuum line attached to it, pull the vacuum line and if you have raw fuel come out, you need to replace the regulator (about $60).

What makes your truck run rough on start-up is, it has to burn up the excess fuel that has seeped into the vacuum line since you shut the truck off last time. When you shut the truck off the fuel pressure regulator lets the excess bleed into the vacuum line and everytime you start the truck, you have to burn this off again. Never ending cycle. Bet money this is your problem.

-slacker :smokin:

As a sidebar, you don't have a distributor cap so don't try to find it.

Checked the fuel pressure regulator already...no raw fuel. Did a fuel pressure test as well....git was good. I am at my wits end.

Could have a small leak at the intake that seals when the engine warms up. Could be sucking coolant or have a vacume leak. Have you been adding coolant lately?

No. No coolant.

Any other ideas?

Finally threw a code after getting extremely worse. P0171 and P0174....running lean. GM wanted to put a new fuel pump on, but I knew that wasn't the problem. A good ole' mechanic found the problem and it now runs like new! I don't remember what they are called exactly, but if you take the top half of the engine off, they are the gaskets that are there. They were almost eaten away and letting air in. Runs great know, and only cost me $100 bucks parts and labor!

My 2000 model 5.3L is/was doing the same thing..took it to the dealer today and they replaced plugs/fuel filter/cleaned throttle body/ and put latest update to the ecu in. I will let you know tomorrow if it does it again.

Mine still has the rough idle and hesitates right after you start it on a cold crank. After a few seconds it doesn't give me any more problems.
---Mulaka, can you tell me what that mechanic did for your truck?

Dude your problem is octane level. Look i dont know what anyone has told you but 93 octane is more expensive for a reason!!!! Its the best type of gas you can put in to your production vehicle!!! Try 93 or 91 octane, throw in some STP fuel injector cleaner. Then on your next fill up do the same thing except this time dont add the cleaner...use octane boost and it will eat away at whatever left over gunk is in the injectors and fuel lines. Then continue using 91 or 93 until you sell it or change it into a race truck!!!

Oh and by the way the new chevy's 99 + are DISTRIBUTORLES meaning there is no ditributor... its runs off coil packs

And if that doesnt work then it means you have a leak somewhere. If you listen to your truck when you're driving with windows close it should sound very smooth on accleration. No ticks no whisper noises, if you here a tick or what sounds like a peice of paper flaping in the wind, then you have a leak of some sort which is either an exhaust leak or an intake leak!!!!! His problem was an intake leak