jvr

Ok so I have two separate problems, but they are related in some way (or at least affect each other).

First, my brake pedal feels spongy... When the engine is on and the car is stopped, pumping the brakes does not increase the pressure I feel in the pedal. But when the engine is off and I pump the brake pedal, it starts pushing back MUCH harder and does not depress all the way to the floor like it does when the engine is running. Could I have a faulty seal in the master cylinder? Would that require a replacement of the MC or can I replace the seal/fluid myself?

Second, my warm idle is low... It hovers right around 400-500rpm, it doesn't jump all over the place or surge, it's just low. HOWEVER, when I pump the brake pedal, the idle goes up to about 750rpm until I stop pumping, at which point it goes back to 4-500.

Would cleaning the fitv, iacv, and tb help the low idle? I haven't checked if that white screw in the fitv is unscrewing itself, but from reading that thread it seems like most of the time that causes a HIGH idle or large surges in rpm, which I don't have... Mine is just lower than it should be.

So, are these issues connected? Should I follow the instructions in that thread for cleaning up the idle system? Or could this possibly be an actual idle set screw problem? I don't want to mess with that until I rule out everything else since that would just hide the real cause.

Thanks for your input.

MAD_MIKE

If the brakes are spongy feeling, then the brake fluid may need to be replaced. If it has been over two years since the fluid has been replaced, the fluid in the reservoir is black, or you use your brakes pretty hard, then the fluid will need to be replaced/bled out.
If you do this via pumping your pedal, prior to opening the system, with the engine on depress your brake pedal. Note how far down it travels, and use a block of wood to prevent it from traveling any farther than the pedal normally would. If you floor the pedal on an older MC it will damage the seals from crud build up inside the MC. The normal traveled area of the pistons is smooth, flooring the pedal would cause the pistons to travel on a rough section which in turn can tear a seal.
No.
When the engine is off, there will be enough vacuum reserve in the brake booster to supply ~3 full booster assist pedal depressions.
As the vacuum reserve is depleted there will be less assist, and the pedal will travel less and less until all assist is gone and you can only depress the pedal as much as your leg can power it down.
This is the normal operation of the brake booster.
With the assist depleted, place your foot on the brake pedal and then start the engine, the pedal will drop back down to its normal boost assisted position.

Does the car ever stall? If not then the idle is fine.
This is a normal function.
When you depress the brake pedal the vacuum is released for a moment to allow the booster to recharge. There is a check valve inside the booster that allows this to happen, it is a necessary function. If you listen closely when you depress the pedal you will hear a slight 'whoosh' from under the dash.
When you rapidly pump the pedal you create an vacuum leak which will cause the engine to rev.
Meh, if the engine is not stalling or causing any other running issues then I would leave it be. If your basing your low idle solely off the Tachometer I would not worry about it unless it is causing you drivability issues.
Are they issues no, well except for the spongey brake pedal.
If the low idle is not causing any driveability issues or stalling I would not worry about it. When turning on the A/C the ECU will command the IACV to open to allow more air in to compensate for the load. So if there are no stalling/drivability issues I would leave it alone.

jvr

There are no issues when I switch on the A/C so I guess the iacv is working properly, however the car has stalled a few times in the last couple weeks when I started it warm (ie, after running into the store and starting it back up after only a couple min of being off). Even when it doesn't stall, it often feels like it bogs down and wants to stall, but doesn't.

As for the brakes, so you think I should just replace the fluid and bleed them? What about replacing the lines, could really old brake lines be contributing to the spongy feel if the fresh fluid doesn't help? These brakes have not been serviced in a long time, other than getting new pads.

MAD_MIKE

Check your ignition components. If the parts are worn or a part is failing the heat soak may cause rough running.
If the old brake hoses are swelling, cracked, blistered, or damaged in anyway then yes, the hose will contribute to a soft or spongy pedal.

Verify your parking brake is also correctly functioning. If it is out of adjustment or the self adjusters are jaming then this will require a bit more pedal travel(creating a long pedal, not spongy).

Tarel

Southern fighting with a brake issue I change the master cylinder I cleaned all the lines but still have no breaks whatsoever when car is off I have little pressure but not a lot been fighting with whether I should change the brake booster or not any ideas