Throttle lag

[Rudyyss]

Hello,

I´m having problem on my corolla 1.4VVT-i  71kW 2006.

When i let of gas pedal, i don´t know if there is vacuum leak, or what, but the engine is still pulling for like another 2 seconds, or when i´m shifting, the RPM increases by cca 500 when clutch is pressed. Throttle body is clean, throttle cable is running smoothly. i´ve changed gasket on intake manifold and checked vacuum hoses. 

Before i dissasambly half of the car, i wanted to ask, if anyone has some experience with this.

[Cyker]

Has it only just started doing this? Some cars do this normally...

 

[oldcodger]

On 2/27/2024 at 6:08 PM, Rudyyss said:

Before i dissasambly half of the car

Would try and locate the cause before doing that otherwise you might introduce a load of new problems.

Clutch and Throttle cables can be deceptive, while apprearing free to move when disconnected , they can fray internally and become sticky when under tension/load.

Have you tried disconnecting the cable at the carb and operating the throttle by hand to see if it gives the same overrrun problem ?

Is the Air Con switched off ?  is your miles per gallon normal  ?

[Rudyyss]

On 2/27/2024 at 9:23 PM, Cyker said:

Has it only just started doing this? Some cars do this normally...

 

When the engine is cold, it´s worse. When it´s up to temp, it´s bit better, but it´s still there. I own the car for 3 years, and this started happening last winter, but nothing major. Since then it´s worse and worse. I tought that i would be gasket between intake manifold and engine block, due to different thermal expansion of materials. But nope, that wasn´t the problem.

[Rudyyss]

On 2/28/2024 at 11:04 AM, oldcodger said:

Would try and locate the cause before doing that otherwise you might introduce a load of new problems.

Clutch and Throttle cables can be deceptive, while apprearing free to move when disconnected , they can fray internally and become sticky when under tension/load.

Have you tried disconnecting the cable at the carb and operating the throttle by hand to see if it gives the same overrrun problem ?

Is the Air Con switched off ?  is your miles per gallon normal  ?

Yes, that´s why i´m asking here, because i have no other idea, where this problem comes from. I´ve tried spraing brake cleaner around tho hoses, gaskets etc. if the RPMs will increase and nothing happend.

Yes yes, i´ve opened the throttle valve by hand and it´s the same, cable is no problem, neither throttle valve. The only thing that comes to my mind right now is  the idle air control valve could be sticking, but i don´t know if that´s the problem, because when i shift for example at 3000RPM, the PRM still inceases cca by 500. Idle air control valve doesn´t have the capacity to alow as much air into the engine, to run at such a high RPMs. Or, when the throttle valve closes, it creates negative preasure in the intake manifold and air is forced through stuck open idle air control valve. I don´t realy know.

A/C does not affect this at all

Fuel consumtion is in my opinion higher, but what i read it´s normal, around 8-9l/100km (26-29mpg). Car passes MOT and emission with no problem.

[Cyker]

What have you checked so far?

My guesses are a dirty MAF sensor or a leaky intake, but these are just random guesses!!

 

[Rudyyss]

1 hour ago, Cyker said:

What have you checked so far?

My guesses are a dirty MAF sensor or a leaky intake, but these are just random guesses!!

 

I've checked throttle body, but not the idle air control valve. Checked hoses for any cracks and changed gasket between manifold and engine block.

How do i look for cracks in manifold? I've sprayed it with carb cleaner and listened for RPM change, but nothing happend.

I don't think it's MAF, i will check it, but i don't think that's the problem. Mainly beacouse the engine is running and starting smoothly. I think if MAF was dirty, the engine will be stalling or running poorly. But i'm not sure if my theory is right.