funny idle

[jase386]

when the 85 caprice is sitting at idle, and the brake pedal is pushed, the engine acts like it wants to die.

could there be a vaccum problem somewhere?
Maybe the idle is too low?



When would the solenoid be activated to raise the idle, only when the AC is on, or when you have it in gear also?

[silicon212]

That, to me, sounds like a failing brake booster. I had that happen on my own car about a month ago.

[PeteA216]

I noticed (in all cars that have vacuum brake boosters) that pressing on the brake results in a temporary higher idle simply due to the fact that all the air in the booster is being let into the intake thus creating a temporary lean mixture. If you pump the brakes you will notice an even greater reaction. But my wothless observation doesn't help you here.

Oh and the kick up solenoid is just when the A/C compressor is on for three reasons: 1. The A/C Compressor puts on extra load which would bog the engine down a bit at idle and 2. An A/C Compressor does not do well at lower RPMs which I've read could result in premature failure to the compressor and not-so-cool air coming out of the vents. Finally 3. Having the A/C on not only puts an extra load on the engine itself, but also the electrical system to keep the compressor clutch engaged, keep the idle kickup engaged, and power the blower motor, so at lower RPMs the altenator may struggle to provide sufficient amperage to the A/C system along with everything else in the vehicle (lights, radio, etc).

P.S. The A/C compressor is engaged when the A/C is on (obviously) and also when you have the defrost on. That way the A/C acts as a dehumidifier, and keeps the system in it's prime even in the winter months. If you are low on freon, the compressor will kick off as will the idle kick-up solenoid.

[bobss396]

Rule out the check valve first, make sure it hasn't popped out and the hose isn't cracked somewhere. Check valves are real cheap and take seconds to change and if it works, you're a hero.

The acid test for a brake booster is to pump the brake pedal with the engine off until you have a solid as a rock pedal. Then start the car with your foot on the pedal and it should drop to where it normally is.

Bob

[GreyGoose006]

the solenoid should kick in when you put it in gear too...
there is extra load when the tc is engaged.

it is adjustable by turning the screw that pushes on the throttle.

[PeteA216]

I don't think the solenoid is supposed to kick in when the vehicke is in gear. Example: When at a stop light, there's no wind coming through the windows I get hot so I kick on the A/C. I hear the clutch kick on & I hear and feel the idle jump up a bit.

[jase386]

to bobs. what check valve are you speaking of? so ill check the correct one.


also, what tells the kick up solenoid to 'kick up'? is there a switch, or sensor somewhere that could be bad, or maybe just the solenoid is bad and not working correctly. i ask this because :

in a previous incident, on a cold morning start, the kickback solenoid was plunging back and forth on its own. the car coughed and sputtered, and the check engine light was coming on and off.

wish some of you fella's lived near greenville sc!!

[silicon212]

Re: check valve:

It's the whitish colored plastic thing that goes into the brake booster, that the engine vacuum line attaches to.

[bobss396]

Just look at the front of the brake booster, it will have a black hose running from it to the manifold. It pops right out of the grommet on the booster.

Your can is doing the funky chicken probably due to the vacuum leak from the booster or check valve, or something else. You can clamp a vise grip on the booster hose temporarily and see if the idle smooths out. At least you'll isolate the problem a little better.

With the car idling, take off the top of the air cleaner, cup your hand over the carb airhorn and is the idle picks up and smooths out, you have a vacuum leak somewhere. Again, rule out the booster/check valve first.

If that doesn't do it, start checking your vacuum hoses, spray around the carb base and EGR with some Gumout to see if it will smooth out and raise the idle. It has to be something relatively simple and should be easy and cheap to fix, unless it is the brake booster.

Bob

[jase386]

also, what tells the kick up solenoid to 'kick up'? is there a switch, or sensor somewhere that could be bad, or maybe just the solenoid is bad and not working correctly

[1988capriceclassic]

Originally Posted by bobss396

Just look at the front of the brake booster, it will have a black hose running from it to the manifold. It pops right out of the grommet on the booster.

Your can is doing the funky chicken probably due to the vacuum leak from the booster or check valve, or something else. You can clamp a vise grip on the booster hose temporarily and see if the idle smooths out. At least you'll isolate the problem a little better.

With the car idling, take off the top of the air cleaner, cup your hand over the carb airhorn and is the idle picks up and smooths out, you have a vacuum leak somewhere. Again, rule out the booster/check valve first.

If that doesn't do it, start checking your vacuum hoses, spray around the carb base and EGR with some Gumout to see if it will smooth out and raise the idle. It has to be something relatively simple and should be easy and cheap to fix, unless it is the brake booster.

Bob

thanks bob i had the same problem and tried what you said above and it works the idle picked up alot feel's normal in going to go to the store and buy all new vac hose's

[bobss396]

You're welcome. Always start out with things that are free or change the most obvious cheap part. Checking vacuum, always a good thing to do. Cars have sooo many hoses which do dry out in time. Carb gaskets, EGR valves are also notorious for leaking on older cars.

Bob