Rough idle/ Vibration

[patcal]

I have had my Corolla for two months now. Got most of what it needs fixed but got one problem I can't figure out. At idle, the RPMs will go down to about 600-700 RPM in drive the whole car starts vibrating. If I put it neutral
the idle goes up about 100-200 RPM and smooths out. There is no issues at any other speed. I have checked for vacuum leaks, double checked the timing, idle speed. Changed the plugs, checked the wires and cap resistance. I have also cleaned the throttle body, checked EGR valve for leaking and the PCV system. What the heck am I missing? If I just nudge the gas pedal while at a stop light the RPM will go up and smooth out. I need some directions to go with this. I am getting about 27MPG in town average. Help.

[tashirosgt]

Are your motor mounts in good condition? Does it have manual or automatic transmission? Have you checked or set the timing? This procedure includes adjusting the idle speed.

[patcal]

I do not know how to check the motor mounts outside of looking at them. It is a 3-spd Auto. I have checked and set the idle speed and timing multiple times.

[tashirosgt]

You can often detect a bad front or rear mount just by looking at it. It should look like a rubber donut with webbing that holds a bolt in it's middle. When they go bad the bolt isn't held in the middle. It drops down or goes to the top of the donut.

If the car shakes in idle, you can wedge a pry bar where a mount is and support the engine. See if the shaking stops.

[patcal]

Cool. I will give that a try. Thanks.

Originally Posted by tashirosgt

You can often detect a bad front or rear mount just by looking at it. It should look like a rubber donut with webbing that holds a bolt in it's middle. When they go bad the bolt isn't held in the middle. It drops down or goes to the top of the donut.

If the car shakes in idle, you can wedge a pry bar where a mount is and support the engine. See if the shaking stops.

[Donald]

Did you set the idle by the book, bridge the ports in the check connector?
Check/clean your idle air control valve, on the bottom of the throttle body.

[patcal]

I did set my idle by the book. I did not remove the throttle body to clean it. It was not very bad but I just sprayed the throat and all ports I could get the needle valve into.

Originally Posted by Donald

Did you set the idle by the book, bridge the ports in the check connector?
Check/clean your idle air control valve, on the bottom of the throttle body.

[toyotaboyfreak]

i have the same car and mine vibrates like crazy too [kinda annoys me], its the engine mounts they are due for change

[patcal]

OK, I have checked my motor mounts & they are fine. Even though the resistance in the wires and cap are well within tolerance is there any value(under 25K ohms) in changing them? I don't want to just throw money at a problem. Any other ideas? I am almost ready to take it to a mechanic.

[RobMilkshakes]

I had a very bad vibration in my celica which was fixed by replacing all the mounts, but your issue sounds like its more of an idle issue. I can rule out the whole mount thing because that wouldn't screw with your idle speed like that.

[Donald]

Idle control valve.

[patcal]

Checked per the FSM and checked out OK. Cleaned with carb cleaner anyway.

Originally Posted by Donald

Idle control valve.

[Donald]

Look for a vacuum leak.

[patcal]

I have. Used carb cleaner while I have a vacuum gauge hooked up. Sprayed all the valves, hoses, manifolds, fuel injectors. Did this two separate times to see if I missed something. Vacuum is rock steady.

[patcal]

Well, today I give in. I am taking to a mechanic. I know when I am beat. Let him figure it out. I will let you all know what he comes up with.