Engine stuttering when idle in D with Brake

[PandaBear]

Car: 95 Corolla 1.6L with 3 speed auto.

It had 2 out of 4 engine/transmission mounts replaced a few years ago, the other 2 that were replaced were "weak" according to my mechanic.

Recently (6 months ago) I replaced the exhaust manifold due to cracks and the gasket between manifold and CAT doesn't fit very well. It was too thick, so I torque it as far as I could without overtightening it (about 30lb/ft or so).

There was a piece of bracket that mount the header to the engine block (short block) that I didn't install back due to clearance issue. Prior to the manifold replacement it was just hanging there with bolt on the engine side but not on the manifold side.

Recently I was stupid enough to try some hyper mile method, driving on the highway and turn of the engine when in Neutral, and restart it when I need to and shift into D while the car is still moving at about 30mph-45mph.

Car has some sticky throttle issue at idle, between idle and the first 5% throttle is very sticky and get stuck, so sometimes I press a little hard and it goes from 0% to 25% from traffic stop, and have to let it down to 10% later.

So my question is, is the mounts bad or is it the exhaust gasket? Or could it be the idle air volume?

 

[Audi Junkie]

Vacuum leak?

 

[BearZDefect]

PandaBear, this isn't directly answering your question, but if your throttle is sticky how about cleaning that throttle body?

Off topic: I wonder how the modern electronic throttle controls will fail when their throttle plate gets sticky for a while.

 

[tom slick]

I also think it could be a vacuum leak, maybe in the brake booster.

 

[PandaBear]

BearZDefect,

It is a cable throttle body. I had it before and I think back then (when I haven't learn how to fix cars yet) the mechanic just put some grease on the cable sheath's opening to lube it up. I got so used to the stickiness that I'm able to control my right foot accordingly, but will fix it when I have time.




The stuttering gradually start and increase when I stay in front of the light, then increase to a point that shake the car. If I moved a little (step on the gas or put in neutral) then it goes back down and will come back after 20-30 secs.

 

[artificialist]

Vacuum leak is likely. On such cars, the plastic components that the vacuum lines are attached to will easily shatter if you try to replace the hoses. Get ready to replace more than hoses.

Also, if the TB is dirty, chances are that the Idle air control passages are also dirty, causing less air to enter the engine.

Does your Toyota have a MAF or VAF? Quite often, the intake tube or resonance chamber behind the sensor will crack open, and air will bypass the sensor causing a false reading. It will also let a significant amount of unfiltered air into the engine

 

[The_Jeff]

Lubing the throttle cable usually won't help and might make it worse as it's got a dry graphite lube from the factory.

Find where the cable actuates the throttle blade itself, you can move the thing with your hand and if it moves freely it's the cable, if it's sticky it's the throttle blade itself (common.) Take your air intake tube off and go at it with throttle body cleaner (best) or carb or brake cleaner (sometimes not recommended) and paper towels.

Don't let more than an ounce of fluid get by before starting the engine and sucking it through the intake.

 

[mechtech2]

All vacuum and intake lines/connections must be perfect. The PCV system is crucial, too.
But maybe you have a dirty sticky throttle body, with possibly a bad Throttle position sensor.
Clean out the TB with solvent and a rag - get it dinner plate clean. This often fixes idle anomalies.
Same for the idle air valve, but be careful with strong solvents getting inside.