twojayzee

Alright guys, I consider myself very competent when it comes to cars. From motor swaps to custom suspensions, but i'm stumped on my brothers IS300.

Its an 01' and when you hit the throttle, the car stumbles. It has lazy acceleration like something is holding it back. The car runs on full synthetic and has only 130k on the odo.

This past weekend we did OEM irridium plugs, new coils, replaced the leaky valve cover gaskets that were dropping oil into the spark plug galley; and no bueno. No difference at all.
Any thoughts ? Plugged injectors, plugged fuel filter, plugged cat ? Those are all things we thought of, but its more money and more time if we cant narrow it down. Bad ignitor... argh !

FIXED ! - UPDATE IN POST #11

abraham198

I have the same issue. If tried the tps and it has been a temporary fix so I'm thinking it might have a bad throttle body. I'm still trying to work on it and see if it can figure out the issue. But no luck yet :/ ..

Black1129

Try cleaning the throttle ( butterfly) and the mas air flow sensor. Then check your tps sensor see if it needs adjustment ( YouTube for help on that) then try. Some fuel cleaner to clear the injectors. And hopefully before anything you did a diagnostic

PIONEER

iTrader: (2)

how about a bad fuel filter or a fuel pump?

twojayzee

I seafoamed the motor and everything inside the throttle body, intake manifold and elsewhere is spotless. No detectable oil or carbon build up.
I suppose the next thing is the fuel filter.

Would there be no CEL if the TPS or MAF were bad ?

Black1129

Could be a clogged cat as well. Did you pull any codes?

twojayzee

That's what I was thinking, but there's no CEL's and I'm not a fan of pulling the header just to check; although it may come down to that.

Black1129

If the car sounds muffled like it has a intake then it could be a cat. Another way to know it to run hard at night and pull over some where dark to see if any of the three cats glow red. If glowing then that's your problem

az989

theres like a call back for 01's for a ecu reflash. that fixed my sluggish acceleration

twojayzee

So... Thinking it was one or more dead cats, we did the only thing car guys do - throw away stock ***** and install aftermarket parts. Now the car has a new header, b-pipe and still drives the same. Any more than 30% throttle and the car starts to choke, let up and the acceleration picks up. Blip the throttle and it chokes for a minute and the revs. Injectors next ? Still absolutely no CEL's

twojayzee

Alright guys, after all that - we drove 100miles out to get a throttle body and MAF.
I dropped in the MAF first since it's only two screws... That was it ! Little cawksuker.
Like I said, I had cleaned the MAF previously but obviously it was no good. So now we have a throttle body to sell...