# 2000 Pontiac Grand Prix rough idle problem (it feels like it is going to stall)



## zamorase (Aug 18, 2011)

My grand prix (year 2000 - 100000+ miles) idle is very rough when almost coming to a stop (like approaching a traffic light or as I am parking). After the incident it is usually fine for the remainder of the trip. When I step on the gas it runs fine - very smooth and powerful. The only problem is when I am slowing down to a stop. It feels almost like it is going to stall. I already clean the EGR valve and replaced the IAC valve but still continue to do this rough idleing, does anybody knows what the problem could be?? 

Anyone's help es very much appreciated !!


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## octaneman (May 13, 2009)

Hi zamorase 

The problem has all the characteristics of a blocked catalytic converter, an exhaust gage will determine if its restricted. Drive your car normally and when the problem occurs have a look underneath where the converter is ( SAFETY FIRST!), if you see the converter cherry red it will need replacing. 

The converter may not be the only source of the problem , a bad fuel pump or regulator can also cause engine stumble. Hook up a fuel pressure tester and take a road test with the gage securely fastened on the windshield. Drive the car until the problem starts and note the pressure reading before and after. If there is a significant gap between readings, then the problem is in the fuel system. 



Note : The computer could have picked up an intermittent fault code which could help with the diagnostics. Extract the codes from the computer but do it right after the stumbling occurs, this way the computer won't have time to self correct the problem. 


post back your findings.


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## bruiser (Jul 30, 2005)

If the Service Engine Soon light is on, get the codes pulled. That should point you in the right direction.


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## Scottg1 (Jul 30, 2011)

It should throw a code but it sounds like a mass airflow sensor. A co worker had a very similar problem on a gtp


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