Rough Idle stalling

[heatseeker]

I've a 1999 Grand AM SE with the 2.4L OHC engine. Car will idle in drive, at a red light, for a while then starts to misfire. Put it in neutral and it will idle normally. Ran computer diagnostics on it and nothing came up. Replaced the following: Coils, coil housing, spark plugs, and spark plug boots. It's strange, car will idle then it starts to misfire. Someone mentioned to me that a dirty fuel filter might cause this. Any clues? Thanks

[carlover626]

Fuel filter could be a part of the problem, also check the Air filter.
How many miles do you have?
Could be the cat as well........

[heatseeker]

63K. I changed the air filter recently. The fuel filter will be next on the list. Someone mentioned the cam position sensor might cause this condition. Any thoughts on that?

Thanks

[carlover626]

To the best of my knowledge you would have a CEL if that was the case.
Maybe you can clean the TB and the Idle Air Control valve with some carb cleaner and get some results? Look around the Throttle Body for a loose hose or a vac leak as well. The charcole canister behind the driver side headlamp could have a loose connection or no connection to the T-fitting.

[heatseeker]

Throttle body was cleaned and hose replaced. I'll check that canister behind the headlamp when I get home.

[xLongIslandcore]

I think I have the same problem, but only notice the "dipping" in rpms when using alot of accessories...it sucks and its gettng worse, im bringing my car in next week but dont know what to tell my mechanic lol. i have a new battery, got the 3 step TB and injector cleaner done recently. so WTF?

How can I tell if i have a vac leak?

[carlover626]

You can spray some Carb cleaner around the TB and vac lines and see if the idle changes.

[rixGAphx]

Originally posted by xLongIslandcore
I think I have the same problem, but only notice the "dipping" in rpms when using alot of accessories...it sucks and it's gettng worse,...I have a new battery
Check the battery cables!! Both ends of both cables must be clean and tight and shiny brite.
If a cable is heavily corroded (especially deep inside the molded rubber boot), it will prevent current from getting from the alternator to the batt and accessories.
This *might* have been what killed the previous battery, and it might be killing the alternator as well as causing such a load as to alter the idle.

How can I tell if I have a vac leak?
Vac lines are all the hoses under the hood that don't carry coolant to the radiator or the heater; or fuel to the fuel rail.
There's a decal on the front passenger strut tower that diagrams the hoses related to emissions; additionally, there is a thick black rubber hose from the intake manifold to the brake booster, and a couple other hoses to the Htr/AC controls and to the vac reservoir (black plastic grapefruit-like ball below the battery.

Test Procedure:
* Get a spray-can of 'Winter Starting Fluid', about $4 at K-mart and such.
* Warm-up engine.
* Have fire extinguisher nearby.
* Be CAREFUL!!
* Move car outdoors.
* Turn engine 'on'.
* At each vac line connection, spray about a 1/2 second shot of fluid.
* If the engine rpm's rise, then there's a leak that has sucked-in some fluid.
* If no change in rpm's, then no leak at that spot.
* Continue with other connections.
Don't spray so many or so fast that you end up with an explosive cloud of unburned fluid just waiting for a spark. :eek:

It's a very accurate procedure, though a little hazardous.
Remember when you were 9 or 10 and learning about fire and explosives?
Remember when you were 11 or 12 and had learned from your mistakes? Just keep them in mind :D :D

Good luck.
-Rick