2002 alero has loss of power

[dnd02alero]

I have a 2002 Alero 3.4L with 100K+ miles, here's the recent problem i'm having, took it on a 300 mile round trip the other day and on the way back it started loosing power when going up hill, then on the straight away as well, i noticed if you let off the gas pedal and let the RPM's drop and then re-apply the gas the power would come back, It used more gas then normal for that length of trip also, i had my local mechanic run a diagnostic test and came back with P300 which is multiple misfire, I had changed plugs and wires at 100K, even pulled each wire off the coil packs to ensure i was getting a good spark,(it was). also changed the fuel filter yesterday and dumped in some gumout fuel system cleaner, I noticed it only does it when it's in gear, if you rev up the RPM's in park it's has plenty of power but when you put it in gear and apply the gas the RPM's will drop within a second and a half to two seconds. Here's the possible's i've read from different post.
1. cataylatic converter clogged
2. coil packs loose spark when they get warm due to a crack at the base
3. using cheap spark plugs. I'm using Iridium AC Delco
4. using cheap wires. i'm using 7mm autolite
5. cheap gas. I filled up with 87 octane as usual before the trip and didn't have any issues until half way back.
Hope I've supplied enough info to help you diagnose my problem.

[BNaylor]

Does it just lose power or does it feel like a misfire condition? I'd have the CAT converter checked out since it will also give off a random or fixed misfire DTC when defective.

[dnd02alero]

It doesn't shudder or hesitate, so i'm pretty sure the spark is fine, just looses power when you put it in drive and apply the gas after a few seconds. For example, If you put it in drive apply the brake and set the RPM's at 2000 it will drop to 1500 or less within a few seconds, I checked the exhaust and it seems to have good flow. Could it be the MFS or another sensor?

[MO2001Alero]

I've got the exact same problem with my 2002 Alero 3.4L w/ 92K. I was hoping you might post your solution.

I've havn't replaced plugs and wires, but just replaced my fuel filter, air filter, and cleaned MFS last night...yet the problem continues.

Problem happens even in Park, if you rev up the engine. It will cut out about 3500RPM and won't go any higher. The tack just jumps from 3500-4000, almost like a misfire. Also no service engine lights or anything...

[BNaylor]

Originally Posted by MO2001Alero

Problem happens even in Park, if you rev up the engine. It will cut out about 3500RPM and won't go any higher. The tack just jumps from 3500-4000, almost like a misfire. Also no service engine lights or anything...

The cut out you get in park or neutral is normal since there is a rev limiter to protect the engine. Kicks in around 3500-4000 rpms.

[MO2001Alero]

SOLUTION FOUND!

My catalytic converter was clogged completely....the muffler shop said this is a common problem with the 3.4 L engines, due to anti-freeze leaking into the exhaust and clogging the catalytic converter. I had them replace it with a new one and the car runs great again!

[dnd02alero]

THANK YOU DREXEL, MISSOURI.

I had the CAT checked and it was completely clogged. $170 bucks later and i'm back on the road. thanks for all the help. bnaylor gets all the credit, he told me to have it checked back in Feb.