Gt Don't Pull Like It Should

[Calebnc302]

Well my 03 gt just don't seem to have the power it should. I've had it 6 months and changed oil, fuel filter, plugs, and cleaned the t body. Also cleaned maf, egr, and iac. First test drive she broke loose in 3rd (it was cold and damp outside) now it maybe chirps in second. Sometimes going 45 in 5th if I hit a slight incline it gets this chug/bog, and u have to give it alot more gas or downshift.rarely though when its running better( this seems to be intermittent but most of the time runs bad) the same hill at the same speed it has no bog and gas pedal barely has to move. Also exhaust note varies slightly when it's running better/worse and sometimes pops on decell/shift more than others. Mpg seems a constant 20. I have no codes except for downstream o2 as I have or x. No misfires or anything drastic, it still runs smooth, and has power, but definitely not what it should have. I'm thinking maybe a sensor or something. Also i replaced the intake due to small coolant leak soon after i bought it. It is hard to tell if it lost power after this as i didnt really drive the car hard for a few months. If there was a tiny air leak or something would it not set a code? The car does have 160000 on it but the insides are very clean as the previous owner puts many hwy miles and maintained it. The reason I know it's not running 100% is because there have been days here and there when it pulled hard and you knew it was right lol. Please help I'm running out of ideas.

 

[ForgedBlack01gt]

I'd fix the code first... whats your budget? are you annoyed and wanting to be creative with good upgrades to make that MIGHT fix your issue? 160,000 miles, I'd run some NOS Offroad Octane Booster/fuel injector cleaner thru there then if that doesn't do it replace the coils... Accell, MSD, etc. make new ones and the stock ones could be malfunctioning (probably not but hey, you're modding anyway right?) ... any white smoke from exhaust? high mileage, could be almost anything dude...

 

[Calebnc302]

Thanks for the reply man and I've ran some sea foam through the intake, and in the gas tank, with no improvement. Also the coils are not originals and were recently changed by the previous owner. Also no smoke, and I don't burn oil. I got the o2 eliminater harness so no more codes. I'm thinking maybe the iac not opening or closing all the way? Because like today my car was fine (squealed the tires in second, and just accelerated quicker with more seat of the pants lol) but tomorrow will prolly be back to its lazy self haha. Also I reset the battery couple days ago and the idle would stay at 1300 till I stopped. Was like that for 100 miles. Now it's fine. So yeah maybe the iac ?