Have an '02 Taurus 6 cyl where the startup and idle down seem normal, but when it's put in gear and allowed to move just with engine idle it has a consistent wave like throttle surge that can easily catch you off guard and propel you too far forward. The surge happens in pulses about a second and a half apart. After you get rolling above 5mph the surge either doesn't happen or isn't noticed. Does it at start up or after a long drive. Been happening for at least 5 years now.

Any idea what's causing this?

 

Cleaned the throttle body and IAC?

 

Yes that's exactly what I'll be doing today, throttle body and IAC.

I've had someone else comment on the problem...

'That scenario is called an idle roll or a warm idle roll. Typically what is happening is a condition that the PCM corrects and then stops and the condition repeats with correction and return to the issue. Unmetered air getting past the throttle body or a vacuum leak or some other lean or rich condition that is corrected and then the correction stops.'

 

After cleaning the main throttle body I was going to clean the IAC valve but found this written on the outside... "Attention: Do not clean inside throttle body or adjust hard stop screw. Special coating on throttle plate and bore."

Again, this was written on the small IAC attached just after the throttle body, although it seems to refer to the throttle body itself. So is this referring just to the smaller 'body' the IAC is installed in or does it refer to the main throttle body with the large pivoting circular flap valve?

And whatever it's referring to, can I clean it despite this warning or should I follow the instruction?

 

The warning is more intended for the Throttle Body.
The TB is coated with a special material that’s supposed to reduce the collected deposits in/on the bore and plate.

Without a warning, some may use harsh cleaners, carb cleaner, wire or stiff nylon brushes, scrapers/picks etc and can/will damage the coating and the potential to damage TPS from excessive wash cleaner..

If you clean the TB, use Throttle Body cleaner on a soft rag, Q-tips etc to swipe the goo from the bore and plate surfaces and edges. No cleaner flooding of the intake. Most times its the TB as cause, and you might try just the TB first.

 

Oh well, now I know. The cleaning consisted of taking the TB completely off and hosing it down w/ TB cleaner, then brushing with an old tooth brush. So whatever I did to it I guess I'll just have to start scheduling cleaning the TB more often if I've damaged that coating.

Good news is the idle control is much better now with no jerks or hesitations, so I'm sure that buildup was the problem.