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1998 Chevrolet C2500 5.7L Engine Racing at High RPMs with Air Leak Symptoms

Model: 1998 chev P/U c2500 Fault Code: C2500 Posted: 2010-11-21 21:17

I'm seeking urgent advice on my 1998 Chevrolet C2500 5.7L V8 engine, which is currently running at excessively high RPMs and producing a noticeable air leak sound. The engine idles smoothly when first started but gradually accelerates from around 900 RPM to approximately 600-1800 RPM within just 10 seconds. I've already replaced the MAF sensor, AIV sensor, and throttle body sensor, and inspected all vacuum hoses, PCV lines, and intake components—no visible leaks were found. The noise appears to originate near the bottom of the throttle body, though no cracks or physical damage are evident. Despite spending significant money on repairs, this issue persists. What other potential causes should I investigate? Any guidance would be greatly appreciated.

Related fault codes
C2500
Comments (4)
Anonymous 2010-11-22 05:52

The intake gaskets could be the source of the leak. Other possibilities include a sticking EGR valve, brake booster issues, or vacuum lines running under the dash to the heater controls—these are common culprits in older trucks like the 1998 C2500.

Anonymous 2010-11-23 17:12

Most of the air and vacuum noise I've heard comes from the intake system, particularly near the throttle body on the left side when standing directly in front of the vehicle. Since all visible vacuum lines have been checked and appear intact, if the leak is inside the intake manifold or throttle body assembly, removal of the throttle body may be necessary for proper diagnosis.

Anonymous 2010-11-23 17:20

What are the next steps after checking the intake components?

Anonymous 2010-11-24 08:33

If you're unable to identify and fix the leak yourself, I'd strongly recommend taking it to a qualified mechanic for professional diagnosis—especially given that this is a high-mileage 1998 C2500 with complex intake system components.