Bad idle Unplugging PCV Valve helps it, any ideas what's wrong?

[Icepick]

I have a surging idle, at 750-800 rpms the car surges up and down by a couple hundred rpm, adjust the idle up to 1000 rpms and it pretty much covers up the surge. I unplugged the pcv valve and the surge went away, replaced the pcv valve and plugged it back in surge is back. What parts are affected by unplugging the PCV valve to Intake manifold vacuum? IAC/IAB? i have cleaned it, maybe i need to replace it.

Any thoughts?

Thanks

 

[xplo89gt]

There's definately a possibility with the IAC. They get a really big carbon build up. Took me awhile of soaking with carb cleaner to clean it up.

Have you tried following the complete idle setting procedure? I dont have it off hand, but it can be found on the corral [corral.net]. It involves disconnecting battery for 20+ min to completely reset computer, adjusting the tbody stop screw, starting car for 2min with accessories on, and off, etc.

Also have you checked for vaccum leaks? You may have another leak somewhere. Check your fuel pressure and TPS as well.

Good luck.

 

[Icepick]

There's definately a possibility with the IAC. They get a really big carbon build up. Took me awhile of soaking with carb cleaner to clean it up.

Have you tried following the complete idle setting procedure? I dont have it off hand, but it can be found on the corral [corral.net]. It involves disconnecting battery for 20+ min to completely reset computer, adjusting the tbody stop screw, starting car for 2min with accessories on, and off, etc.

Also have you checked for vaccum leaks? You may have another leak somewhere. Check your fuel pressure and TPS as well.

Good luck.

I just went and bought a new IAC motor, i'm resetting the computer now to do the idle adjust procedure, i did check for vacuum leaks, but i don't know how thorough of a job i did, i did find one, but i already plugged that with no difference.

 

[jaymac]

did you happen to replace the crankcase vent filter as well??? It should be replaced w/ the PCV valve, but alot of people don't do it. It is located in the tube that the rubber PCV grommet plugs into. Take out the rubber grommet (if it's dried or cracked replace itwhile you're at it.), then take a pair of needle nose pliers and stick them down in the tube and grab onto the filter and pull it out. It will most likely be black, oily and grimy. Make sure you pick up a new filter first, you might need to get it from Ford. Then just pop the new one in with the new grommet and you SHOULD be good to go.
give it a shot....

 

[Icepick]

ah, i didnt even know that was down in there lol, i guess back to the dealer i will go

BTW:

i replaced the iac, it idles pretty good at 800 rpm,

BUT:

when you have the a/c on and give a little rev in neutral then release the gas at say 2k rpms, the engine idles down and almost stalls at about 550-600 rpm, then it revs up to about 1krpm and settles back at it's idle speed. Is there a way to fix it? Is it normal that the a/c draws that much power from the engine. If you turn up the idle a little to about 950 rpm, it only drops to about 650 rpm before reving back up and then settling down to base idle.

 

[xplo89gt]

it sounds like a vacuum leak...

check all your hoses, make sure there are none missing.
make sure none look brittle or old...

you could spray a bit of carb cleaner on the hoses and intake area, if the car revs when you spray, then that's your leak.

by the way, carb cleaner is flammable.. so take caution.

 

[Icepick]

ok, i sprayed some carb cleaner on all the engine compartment vacuum points that i could find, they all seemed fine, only time the engine revved was when i pulled on and spayed into it. It might very well be a leak elsewhere, while pumping the brakes if i rev the engine with the engine on the idle is fine, if i dont pump the brakes while giving a quick rev the car almost dies and has to play "catch up"

Any ideas on what vacuum points i should check elsewhere?

 

[xplo89gt]

Did you replace the PCV screen and valve? Did you spray on the lower to upper intake gaskets? Have you checked timing, fuel pressure, and tps?

 

[Icepick]

Yes i replaced the grommet, pcv valve and crankcase breather filter. Timing is good, Fuel pressure i have not checked, I also did not spray on the intake gasket, i am going on the assumption that when the shop installed it about 6 months ago that they did a good job (since i think that, that's probably exactly where the leak is lol)

I haven't checked the tps voltage either, i heard some mixed opinions on that and never bothered tapping the wire to check it.