spboys

I have a 2003 Tahoe that is giving us problems. The truck stalls at stops/lights or when making turns. We replaced the fuel filter and fuel pump, but it is still doing it. We noticed that if you give it gas to keep the rpms up the lights on the truck get bright but once you take your foot of the gas the rpms drop and the lights dimm and the truck stalls... What could be causing this?

RedBoat

Sounds like you alternator is bad. It cannot provide enough voltage at idle to keep it running.

spboys

We will check out the Alternator....... Thanks for your help....

in2pro

If it were the alternator / generator I would think the battery would be going dead at some point.
I would have the fuel pressure checked as the pump could be weak, if thats good then I would suspect the Idle air control.

spboys

We took the battery and had it tested, they said the battery is ok. Would the fuel pressure or Idle air control cause the lights to dimm when the rpms are low?

73shark

Did you get the alternator checked along w/ the battery? If the IAC is dirty and/or bad, it could cause the idle to be so low that the alt couldn't put out enuf voltage and then the lites would dim. But I agree w/ in2pro. Get the fuel pressure checked.

MDTAHOE

You may have two problems happening. I have seen GM battery bolts wreak havoc on may technitions. They can cause a aray of problems. The bolt may or may not look bad. This could possibly take care of your lights and maybe even you stall,providing alternator tests could. Remeber that amperage is more important than voltage when testing alternator.You can not just take a volt meter and measure charging voltage and assume it is good. Also just because a part is new does not mean it is good (fuel pump). Did anything change when pump and filter were replaced? Is the check engine light comming on? What does it feel like when it stalls? Like key was turned off? Like running out of gas? Like as if you did not push clucth in if it was a manual trans?

in2pro

dido what MDTAHOE says on the amperage just because a battery reads 12.5volts doesnt mean its producing full amperage.

I'm thinking its an idle control issue, something else to consider is a vacuum leak.
You might also try cleaing up the throttle body, make sure the throttle plate is closing completely, a stuck EGR valve could also casue idle issues...

spboys

We replaced the fuel pump again, thinking we got a bad fuel pump but the truck is doing the same thing. We had the battery and the alternator both checked last night and they both are good. We had a tune up done on it last night because they thought it might be misfiring but it is still doing the same thing. The truck starts with no problem and will stay running so long as you are giving it gas but once you stop the rpms drop and the truck stalls.It doesn't actlike it is running out of gas where it sputters, it just slowly dies out on you. The check engine light is not on and never has came on.

in2pro

Found this...

See bulletin below.

Bulletin No.: 04-06-04-040
TECHNICAL
Subject:
Idle Instability, Low or Rough Idle with Electronic Throttle Control (Clean Throttle Body)
Models:
2002-2003 Cadillac Escalade, Escalade EXT
2000-2003 Chevrolet Silverado, Suburban, Tahoe
2002-2003 Chevrolet Avalanche
2000-2003 GMC Sierra, Yukon, Yukon XL
with 4.8L, 5.3L or 6.0L V8 Engine (VINs V, T, Z, N, U - RPOs LR4, LM7, L59, LQ9, LQ4) and Electronic Throttle Control
Condition
Some owners may comment on an idle instability, low idle speed or rough idle.
Cause
Condition may be caused by deposits in the throttle body bore.
Correction
Clean throttle body bore and throttle valve plate of carbon using a shop rag and an appropriate cleaner. Refer to Engine Controls Repair Procedures - Throttle Body Cleaning Procedure. This procedure may be performed at any mileage necessary. Check to determine if the PCM calibration has been previously updated to one that includes the update for throttle body coking. For 2003 model year vehicles, look in the operating system portion of the calibration. For 2000-2002 model year vehicles, look in the engine portion of the calibration. If not, then update the PCM calibration to the latest calibration.