so I've been having this lack of performance for a while. sometimes it works great awesome and sometimes it seems like it's restricted and it really pisses me off because I've had some close calls where i needed gas but it accelerated slowly.
I swapped my MAF already. I saw some improvement but still sucks (and my gas mileage decreased a little)
- Before swapping the MAF I was getting roughly 10.2L/100km but now it seems to be 11.3 ish. Perhaps because gas stations have changed their gas to summer? or perhaps my driving not sure. not too relevant I don't really care about this problem.

I've noticed that the longer I drive the vehicle (bring her to operating temp for a while) the performance starts to suck more. Where as when the vehicle has just been turned on to the point where it has just reached operating temp the car works great.

But as for the lack of performance, yes I do have the famous 3.5L rattle.
Should I replace the precats? if so, what should I tell my mechanic when I bring her in? and roughly how much would it cost?
could it be my precats that's been the problem all along?

 

I have a similar issue, someone had blamed my knock sensor while someone else said that vq35s just slow down when hot

 

If it slows when it reaches operating temp then it's most likely knock sensor or at least some other sensor (but not maf).

I'm seeing a lot of these threads lately...

 

How many miles on the car - could it be your catalytic converter?

 

is the ECU throwing any codes at ya?

 

no codes. 63k miles.

 

Welcome to Florida

 

With only 63k I wouldn't think the pre cats are bad maybe knock sensor but if it is the cats get some Cattman Headers instead!!

 

should the 20-30 dollar ebay knock sensors do the job? like these

http://cgi.ebay.com/ebaymotors/ws/eB...m=130397695462
http://cgi.ebay.com/ebaymotors/99-00...Q5fAccessories

 

Do the resistor test 1st to see. I've posted it on about 5 threads, now.

 

heat soak does diminish performance.

the solution

NWP SPACERS ..

 

Cold air runs better in engines try a cold air intake. Just easy but idk mite help

 

^ what he said or go back to stock intake...it will help alot in the hot weather, because as you drive more like you said it gets worse as the heat builds up in the engine

 

No. CAI is not the solution. SRIs provide better gains on our cars. NWP spacers ARE the solution! Especially if you have a 5.5 gen.

 

Where do you notice the power loss? High RPM? Do you run premium?
If the car has more power initially and then losses it as you run it could well
be heat soak as others have mentioned. NWP ! ! !

 

its hot so what do you expect lol im in dc and its 107 let your car cool down for a little ..

 

^ listen to the above. Cooler temps mix better with fuel..... Giving better performance.. However don't expect ridiculous difference, it's 100+ here.. Heat will kill power on cars, Especially our vq's from what I hear.

 

With temp 102 this week in jersey the old gal isn't as peppy as when it was 10 degrees out. But it's to be expected! Everything, man and machine, are moving slow in the excessive heat this week!!

 

Bigtime heat here too...105+...Funny though, my car still chirps 2nd quite easily with the A/C on full and not revving it that hard at all...Could be my mods though...

 

No codes or no CEL?
There is a difference.

My P1800 VIAS code did not throw a CEL, but most definitely affects performance. (wonky VIAS)

Food for thought.

 

Hot air is less dense, therefore cars make less power in the heat.