99 Tahoe idles ruff sputters and bogs !!! HELP

surfnobc2 · #1 10-04-2007, 05:48 PM

Hi everyone,

I have a 99 tahoe 2d 350 4x4 , im haveing a real bad problem with it.

It idles a little ruff the kind that just gets on your nerves. sputters sometimes when it hits about 2k rpms in 3rd gear, and when the air is on it runs ruff and bogs bad but the ruff idle goes away ??? !! I have changed cap rotor plugs wires fuel filter and BOTH CATS !!! nothing has helped and its costing me MONEY !!! I also have a VERY loud fuel pump .. it whines and sometimes you can hear it going in a nd out when i stand behind it . ITs powerful sometimes but its very rare ... it also feels like its just dropping into the gears sometimes ... but sometimes its smooth as can be ... sometimes it starts strong and then sometimes it sucks ... im stuck someone please help me out ..

maxwedge · #2 10-04-2007, 06:48 PM

Get the fuel pressure tested, you need 60-65 psi.

surfnobc2 · #3 10-04-2007, 07:30 PM

sorry i meant to say that as well ... it was tested warm start 55-58 no loss of pressure

maxwedge · #4 10-05-2007, 03:23 PM

too low.

Treblig70 · #5 10-05-2007, 06:41 PM

I also have a 99 Tahoe 350 but it's a 2WD. I had similar problems so I checked my fuel pressure...it was around 55 so every said to change the pump. I did and I guess in most cases it fixes the problem. After I installed the new pump my pressure only increased about 2-3 lbs and my tahoe ran about the same. After changing everything including the distributor I finally took it to the dealer. They hooked-up their computer and took it for a ride. During the test run the intake gasket blew out and water went everywhere. Long story short....the intake manifold had corroded causing the leak but more importantly when I removed the intake I found that the fuel lines had been leaking inside the intake (only air should be in the intake). The leaking fuel lines is a common problem with these engines. Chevy has even come out with a modified spider assembly to fix the problem. I had to buy a new intake and a spider assy but MAN DOES MY TAHOE RUN GOOD NOW!!! The fuel pressure is still around 57-58 but it doesn't matter if your spider assy doesn't leak.

So check your fuel pressure but don't put all your eggs in one basket!!Gil in Tex

surfnobc2 · #6 10-06-2007, 08:07 AM

the thing is it only sputters and bogs when i turn the air on .. and the sputter i am tlking about is a constant sputter ... around 1500 rpms when air is on it hesitates to switch gears ... but when air is off it doesnt do any of that. I dont know when im driving down the inerstate and i want to to pass someone i can stomp it and get around fast .. if it were the intake (dont know if this is right) but shouldnt that not work ??? When i go up hills without air on (steep hills) it doesnt switch to a lower gear until maybe the top ?? Also i have noticed my oil pressure drop it stays at about 20 while idleing now and it just started doing that like last week .. it rises to about 39 and 42 if i gun it ... shouldnt that be higher ... ?? maybe that will help more

i know the intake manifold is $$$$

MT-2500 · #7 10-06-2007, 09:58 AM

As Maxwedge said.
Fuel pressure is low.
You need to get the fuel pressure up to par first thing.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and no run right fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

Treblig70 · #8 10-06-2007, 11:34 AM

After reading your explaination of what happens when you drive with the AC I would do more troubleshooting. My Tahoe would mostly sputter and bog during acceleration or going uphill. It would also idle funny (fluctuating idle). The intake and spider were expensive but it made my Tahoe run like new and the dealership says that leaking spiders are a common problem on these models. I don't know what to think about the fuel pressure, mine has never been above 58 (even after replacement) and my Tahoe runs great. I won't argue with the specs but I also won't complain about the great performance I get. Replacing the spider also made my evap system code (service engine light) go away permanently...... Good Luck!!Gil in Tex

surfnobc2 · #9 10-06-2007, 07:43 PM

i have another question ... the battery connectors are kind of old and have tarnish on them ... and some electrical tape ... would this have anything to do with the bad idle ... and at night when my interior lights are on they flicker a little bit ... ???

envoyxuv · #10 10-06-2007, 10:44 PM

There you go, dude! Make sure your connections are clean and tight at the battery. Don't just look at them, take them both off and inspect them. If the battery bolts are corroded/stripped, replace them! If the positive battery post is leaking acid, replace it! Poor connections at the battery can cause all kinds of problems.

surfnobc2 · #11 10-07-2007, 10:10 PM

i was driving the tahoe home from Mississippi state today (GO DAWGS! ) and i was almost home and i had i little less than quarter of a tank .. the needle on my gauge stopped jumping around and acting crazy and for once it didnt move but when it didnt move and wasnt acting crazy it drove like a dream !!!! has anyone every had this happen .. im leaning more and more towards the fuel pump !!!!! ... also the ruff idle went away when the needle was calm...

surfnobc2 · #12 10-08-2007, 03:05 PM

i dont know if this has anything to do with this .... but if one of my u joints is bad could it be making it run slower ... i had one mess up that made it make a noise when i switched from park to reverse but is there another. When i accelerate fast from stop it feels like my car vibrates ... also does the same when im switching gears sometimes .... but not if i just gradually go ...

MT-2500 · #13 10-08-2007, 04:28 PM

How is the fuel pressure?

surfnobc2 · #14 10-08-2007, 05:55 PM

when i drive at a steady speed the tahoes rpms jump randomly maybe once or twice in an hour ... they jump and go right back down .. when i have my cruise control on and it happens it shuts it off ... and it does it still when im pressing the pedal .. ??? any ideas is this anywhere closely connected to the fuel pump ???

surfnobc2 · #15 10-10-2007, 05:18 PM

I just got my plugs put in about a month ago ... im still wandering if maybe one of the plugs is bad .. this freakin sucks ... it runs fine with air off ... not so good and great loss of power with air on ... whats the DEAL !!!! ... could turning on the air be messing with electrical things (fuel pump ) i can pull a trailer with a full load and it never sputter but when i turn the air on .. its sucks !!!!

so i mean maybe its not the plugs .. but there is still a rough idle regardless all the time ...

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