1996 GMG having problems

I have a 1996 Grand Marquis I went to the auto store and had a dignostic test performed. It popped up a code 0420 which means catalic below thresshold bank 1. I changed the 02 sensors, put a trottle air sensor, a gas cap,My questions is when I start the car it runs, but it doesn't idle, when driving doesn't idle when I come to a stop. When I turn the car off it takes me about a hour to start it back up.What can be wrong with my car? Anybody please help.:frown:

what about the idle air control motor that would be my guess because you said it doesnt idle at start up right then that would be my guess

when you say "does'nt idle", you mean dies or races too high.

It idles right but I'm having a problem with it still. Ican drive it as long as I don't turn it off otherwise it takes me about 30 minutes to start

Replace the Idle Air Control Valve.


Engine - Hard Starting/Long Crank/Stalling
Article No.
97-9-5

04/28/97

LONG CRANK - STICKING IDLE AIR CONTROL (IAC) VALVE - VEHICLES BUILT FROM 11/1/94 THROUGH 3/30/96

STALL - AFTER STARTING WHEN ENGINE ALLOWED TO SOAK FROM 1-4 HOURS - STICKING IDLE AIR CONTROL (IAC) VALVE - VEHICLES BUILT FROM 1/11/94 THROUGH 3/30/96

FORD:
1995-96 CONTOUR, CROWN VICTORIA, ESCORT, TAURUS, THUNDERBIRD
1996 MUSTANG

LINCOLN-MERCURY:
1995-96 CONTINENTAL, COUGAR, GRAND MARQUIS, MARK VIII, MYSTIQUE, SABLE, TOWN CAR, TRACER
LIGHT TRUCK:
1995-96 AEROSTAR, BRONCO, ECONOLINE, F-150-350 SERIES, RANGER, WINDSTAR

1996 EXPLORER

This TSB article is being republished in its entirety to include the 1995 4.6L Thunderbird/Cougar.

ISSUE:
After a 1-4 hour engine soak time, long crank times and/or long crank to start followed by a stall may occur on some vehicles. No further stalling or rough idle will occur after the engine is running. The long crank and/or stall may be due to the Idle Air Control (IAC) Valve sticking.

ACTION:
Replace the AC Valve with a revised AC Valve if no Diagnostic Trouble Codes (DTCs) are present. Refer to the following Service Procedure for details.

SERVICE PROCEDURE

1. Perform normal diagnostics and correct any DTCs as required by referring to the appropriate year Powertrain Control/Emissions Diagnosis (PC/ED) Service Manual.

2. If no codes are present, replace the AC Valve by referring to the appropriate model/year Service Manual, Section 03-14. Refer to the following Idle Air Control Valve Application Chart for proper IAC usage.


http://partimages.genpt.com/partimages/94628.jpg

but if you just replaced the iac are you sure you connected everything when you replcaed it?