740 rough idle

[Deeseven]

Hi there my 740 gl was idling rough so I replaced the Idle air control valve. The car runs much better now (doesn't think about stalling out at red lights) but it still idles rough in drive. If I switch to neutral or park the roughness is not noticeable. Any pointers or tips are greatly appreciated.

[billofdurham]

How long is it since the throttle body was cleaned? This is a task generally overlooked and can cause idle problems.

When the crankcase ventilation system passes blow-by gases into the throttle housing they carry oil residue with them. When this residue hits the hot throttle blade it condenses due to reduced pressure and temperature inside the bore and coats it with a varnish-like deposits that restrict airflow around the throttle blade. The ECU tries to compensate for the restricted air flow by adjusting the idle air control valve but it often can't compensate enough.

Have a look into the top of the throttle body and see what colour the parts are.

Bill.