Lack of power

2002 Buick Century 3.1. 78,000 miles. Noticed lately that it lacks power going up hills. It won't much go above 35 unless I kick it into overdrive. Also a slight miss is sometimes noticeable when driving on highway. Fuel filter? Spark plugs? Also researching the plugs I found the iridium plug is the OEM plug? Should I stay with that or go platinum or regular? One last ? does the engine need rolled back to change the back 3 plugs?

Platinum or irid will do, certainly the filter, yes roll the engine for the rear.

Stay with the Iridium plugs if that is what came in the car. When you are driving does the engine rev and the car does not want to move or does the engine not rev at all and the car is sluggish? If the engine revs but the car does not move you may have a transmission issue. If it does not rev you may have a problem with the catalytic converter. There is a problem with certain 2001 and 2002 GM cars with bad converters. You may want to check with the dealer to see if your car is one of the models with this problem. If so they will repair it for free and give you an extended warranty.

What do you mean "roll the engine" to change the rear plugs?

Steve L.

Due to clearance issues on these vehicles the front motor mounts need to be removed and the engine rotated toward the front of the car. The plugs can be reached more easily and then the engine rotated back into the normal position. They make engine tilters that do this job for you and only cost about $50 if you want to go that direction.

It's not a transmission problem. Catalytic converter?-I never thought of that. It runs fine on flat ground just doesn't have any power on the steep hills. I bought a fuel filter & plugs & will change them first chance I get.

If you find the plugs are extremely dirty that can be an indication that the convertor is plugged or partially plugged. When this happens it tends to cause exhaust gasses to back up into the cylinders and foul the plugs.

Well, I changed the fuel filter & the iridium plugs. Old plugs looked fine. No difference, still lacks power. I'm not getting a check engine light or anything. Any other suggestions?

Have the cat checked at an exhaust shop. I still think that the cat is causing your problem.

My 1998 did this about 2 years ago and I put it in the shop after I could not figure it out. They had it 30 days and could not figure it out. Turned out to be the Electric EGR valve. Disconnect the plug and it will give a code and go into limp mode. Mine had more power right away-thou not back to its old self. I swaped in a junkyard unit and my car was back to new. Hope this helps. Good Luck

Well, as GTP said it turned out to be the catalytic converter. Took it to a chevy garage & they replaced it under warranty. Warranty period was 80,000 miles, I had 79,600! Got lucky for a change. Runs great now.