Car engine racing while on idle

I have 1998 Isuzu Rodeo and last week its engine RPM would be at 3000 RPM even when I am standing at a stop sign. Can someone help identify the problem?

Is there a check engine light on? Have the codes read. It's probably a problem with the idle control valve on the throttle body.

Engine light is not on but after driving my Rodeo for about 30 minutes, engine starts to run at higher RPM even when I am standing at a stop sign. I checked the pipes and there is no leak in the pipes or hoses. Could it be an issue with EGR valve?

You can eliminate the EGR valve. If it wasn't opening when it should, it would simply throw a code, if it was open when it shouldn't be, it would run rough or perhaps not at all.

The problem could be a number of things. The easiest things to check would be to look for vacuum leaks. Loose intake hoses, broken, cracked or loose vacuum lines and perhaps bad intake manifold gaskets. These engines are known for cracking intake gaskets. Carefully spraying around the intake gasket surfaces with carb spray and looking for a change in idle will give a clue. Just be careful and keep a fire extinguisher close. Using WD40 might be a safer thing to use but it would leave a mess.

TPS (throttle position sensor). Don't get a big box store one, either. Get the Isuzu part.