My car is idling so badly that sometimes it just shuts off altogether. It drives great sometimes and my gas mileage in town is still about the same (15-16mpg). The bad idling is intermittent but is much worse if the car has been sitting in the Florida sun for a few hours. If I leave it in park and rev the engine up to about 3750-4000 RPMs I have a better chance of getting it to duplicate the bad idle if this mean anything.

Also every now and again it will bump and lurch while I’m driving but not if I am applying gas. Only if I am coasting and trying to maintain a certain speed will she lurch. A tap of the gas pedal seems to cure knock her back into shape.

Any ideas? Fuel pump? Fuel regulator? Injector? Bad coil (new OEM plugs by the way)? Could it be as simple as cleaning the IAC and CAS? Maybe a new MAF?

I’ll stop babbling and let someone help. Thanks fellers!

I suspect your IAC (also called AAC) valve is either plugged or disconnected. Check the connector first. If it needs to be cleaned, it can be pulled off by removing the four bolts on the back of it.

However, the symptoms you describe really could be any number of the items you list, esp. the MAF.

Fuel pressure problems usually cause drivablity symptoms, low power under acceleration and such.

Ignition problems (except timing) are also more often across the spectrum - problems at all rpm's

I might suspect the MAF only because you report ocassional hicups when driving.

Idle rpm changes [with age/dirt] are slow and progressive. Brand new the space under the butterfly valve and the mechanical air bypass [what the screw on IAC adjusts] in the IAC provide 90% of the required idle air flow. Probably divided 50/50 between the two paths. The IAC adds air after the butterfly valve.

The ecu controls a solenoid in IAC that adds puffs of air to control the idle speed. This should add 10-15% more air. When the AC is on this might increase to 30-40%. When the alternator load is heavy this might be 20%, when the engine is loaded in a low speed parallel park this might add 20%............generally 40-45% is as high as you see regardless of extra load.
When you are traveling at 60 mph and get off the throttle the IAC duty cycle may be 70> 60 >50% so the engine doesn't die when the throttle is suddenly closed.
An 80% duty cycle on IAC may result in a 1200 rpm idle.

The IAC is tested with Consult: 0% idle speed =550-575 rpm, 20%=675-700-725 rpm, 80% =1100-1200 rpms.
Hopefully you can see the effects of a dirty IAC, the dynamic control range of the ecu as to idle speed or slow down speed or load changes is compromised.

Cleaning the throttle body is only half the equation! The IAC gasket always fails on removal have a spare on hand!

-Jesda

Careful the solenoid rod and bore valve is spring loaded to make sure the valve snaps closed when solenoid duty cycle is complete.

Think of the pick tools a dentist uses to clean teeth after the spray solvent soaks.......don't submerge the solenoid or the unit.

Exercise the solenoid with 12 volts to check function.

Careful removing the valve from the expensive hoses, a cracked hose will mean plenum removal to replace!

The manual reads "The ECU actuated the AAC (Auxilary Air Control) valve by an ON/OFF pulse. The longer that ON duty is left on, the larger the amount of air that will flow through the AAC valve."

Its attached right behind the plenum halfway between the driver and passenger side toward the firewall. It also has a hose going out the bottom and a metal cylinder coming out the side. I removed the four bolts holding it on, then unclamped the hose and very slowly and carefully pulled the hose off.

I then used a philips head screwdriver to remove the metal cylinder and sprayed carb cleaner in every nook and cranny I could. Per Dennis' instructions, I did not soak it.

I really cant tell if it made a difference in idle quality, because my particular problem is caused by a bad MAF. It has a plastic idle adjustment screw on it that most folks suggest not messing with, since its hard to get the idle right. But I needed to get to school and the company van wasnt always available to me, so I upped the idle by loosening the screw to keep the revs up. I'll have to go through the trouble of precisely trying to set the idle once my new (used) MAF arrives later this week. Some photos are attached.

-Jesda

Set the idle so that its at 650-700 RPMs... The idle will always be low until you clean the plenum... SO get it where its liveable, and then precision will come when the plenum is spotless......

Set it 2.5 to 3.5 turn out and live with the idle speed result or fix the dirt problem

Whats a new IAC /ACC cost ?