Pontiac Repair: 1991 pontiac grandprix v6 3.4 twin dual cam, pontiac grandprix, intake manifold gasket

Question
hi:I have a problem with the car idling to high when its a cold start up. I checked the tps and it is functioning allright it races up to 3 rpm and after about 10 or 15 min it drops to one or one and a half rpm all the vacume lines are connected and working i cant figure it out, can you help thanks Randy.

Answer
Hi Randy.

I just fished this out of the question pool sorry for the delay. You more than likely do have a vacuum leak the lower intake manifold gasket's go bad on that engine and suck in fresh air. take that cover off the top of the engine and start it up cold and spray some carb cleaner around at the bottom of the intake. If the idle changes or it starts to stumble you found the leak. it' pretty common. One other though is if you have a scan tool check the tp % at idle on a cold start it it shoes anything other than 0% then you have a bad A/C pressure transducer on the high A/C line it's shorting ut and taking the 5 volt refrence for the TP sensore out. Good luck :)