Hi All.

I have a weird problem happening to me on my 1996 Accord EX Wagon.

I installed a new brake master cylinder because of a mushy brake pedal and it slowly moving toward the floor.

The pedal is nice and firm now but after a little bit of driving I came home and parked the car and put it in park and the idle started surging from around 900 - 1000 rpm up to about 1500 rpm and then after a second drops and then after another second heads back to 1500 and it keeps cycling like this.

Did I miss something? I think I can hear a hiss by the master cylinder but is it fuel or an air leak? I sprayed some soapy water in the area looking for bubbles and even felt with my fingers but nothing.

Any other clues?

Thanks.

 

Sounds like you mised the vacume line that conects to the intake plenum from the master cylinder.

Either that or it has a leak. This is a big fat air hose located ontop of the brake booster. (the thing your master cylinder attaches to)

 

Oh, I thought of that one. It is all hooked up with the valve in between the hoses.
I might have to look closer for a crack. The funny thing is that when you first start the car cold this does not happen. Only after warming up.

 

If it's an air leak, it would be sucking IN. That would explain why you don't see bubbles.

Did you check the length of the MC piston rod? Old & new exactly the same length?

 

Also check the intake plenum for little exposed nipples where an air hose can be attached to. There can be a few tricky ones to see.

Trace all the vacume lines one by one in that area. Look for connections that are broken or cracked lines.

 

That is true. I will maybe replace some hose and see if it goes away.
I hope the length of the piston rod is correct. I purchased a genuine honda master cylinder. I might have to check again.

 

I know there was 2 small hoses which have been reconnected in the correct order on the intake manifold and then the large hose above the master cylinder. Maybe one of them cracked after just age. They still seem pretty flexible.

 

Genuine Honda MC seems to be good about the piston rod length (from what I've heard). People have said that aftermarket brands can have different length, & then you have to compensate by adjusting the pushrod from the pedal.

Check for double-gasket between the MC & the vacuum booster. I remember at least one thread where the old gasket stuck on the booster & he didn't notice (vacuum leak).

 

remove the brake master again,, there is a seal at the end of cylinder rod,,,,,,,make sure that it is there and also make sure that there is only one seal,,

 

The seal is #3 in the picture. There should be exactly one.