Erratic idle

[Mikey v8]

Hello from the UK again!

My next problem with the car is an erratic idle. Its fine when its cold, and ok ish when its upto temp, but if its left to cool down for say 10-15 mins and you restart it the idle speed fluctuates between 800-400 rpm quite wildly, feels like it will stall, its worse when you engage a gear too, after a few mins driving its much better but still not 100%, only time is steady is when its started from cold.

Any ideas?

 

[WhalePirot]

Is the car stock or engine modified? It really helps to have background and there is none I found in your profile or signature.

A few things can cause the hunting idle as the ECM gets confused by data fed to it that is literally off the data charts, from modified components.

I start with the basics as with any engine: basic tune including vacuum gauge readings, plug reading and exhaust pipe color. Add any codes from an OBD reader.

 

[djsroknrol]

Along with what WhalePirot mentioned, you might check the idle air control valve and your EGR valve; they've been known to create symptoms like you described...good luck with it

 

[Mikey v8]

Thanks for the help so far, yes the engine is a stock l98, it was rebuilt 15000 miles ago, how do I check the idle control valve?