boggiling minds everywhere
 

this is a challenge to all. i receltly noticed my car doing this. i didnt add anything new or change anything recently.

ok heres the problem motor running in park. start to slowly press the gas pedal and at about 1800 rpms or 2000 all of a sudden the tach rpms will drop to 1000.. i continue to press the gas pedal more and it rpms go up..then at 3000 or so it will jump about 800 rpms to almost 4000. if i let go of the pedal then the rpms start to drop and when it gets to 2000 the tack bounces back up a little and then falls back to idle. my conclution was a vaccume leak somewhere.. but i alredy tried carb cleaner and didnt fine any leaks anywhere. i guess my question is what opens or changes around 2000 rpm that is leaking? i though it was the pcv valve but i replaced the hose from the carb..the valve is fine. does the valve have to have a air tight seal to the valve cover? what else could it be? im shure the carb is fine its pretty new. any ideas at all? gas milage and performance suck when this happens. thanks

Just clarifying, Is the engine doing this? or just the tach?

What kind of igntion? Is the distributer vac advance? is the carb vac advance? How old is the motor/dis? Does it only happen in park? What happens on the road?

hey, i was wondering the same thing. is the engine doing this or is it the tach. i have a P.O.S. tach and it does the same thing.

im pretty shure the motor is doing this because i can hear the revs go up and down with the tach reading. also it does this in park and drive. in the morning when its cold the motor will almost stall around the 2000 rpm where the revs drop from what i guessing is a lean condition because of a vaccume leak i guess.

First thing I would do is a carb rebuild. It sounds like it is not coming off the idle circuit correctly. To check for a vacuum leak, spray wd40 around the carb and intake while it is running. If you have a vacuum leak, when the wd40 hits it and gets sucked in it will cause the engine to rev up. But I am doubious of an intermitent vac leak unless the carb is really messed up. Could be wrong though.

the carb is about 7 months old and iv tried looking for vaccume leaks with carb cleaner and starting fluid but found nothing. also i am not running any vaccume accessories or vaccume advace.

I'm with you Thunderbolt, sounds like the carb is not adjusted correctly.

"in the morning when its cold the motor will almost stall around the 2000 rpm where the revs drop from what i guessing is a lean condition because of a vaccume leak i guess "

Is this only happening now when it's cold outside? Is the choke working properly? I know it probably is but I had to ask! lol Do you have a "spare" carb that you know works, try it on to make sure it's not your carb. How big is the cam you're running? If its radical, the idle circuit will have to be adjusted/or modified to provide a smooth transition. But it has to be one hell of a cam!

i dont have another carb. and i have stock cam so i dont think its that. the carb is new actually. i have this problem is the morning and after i have ben driving the car for a while. also when this occours i get maybe 2 miles to the gallon.. my gas just dissapeaers. i thinking because of the vaccume leak my vaccume level is low and my secondaries come on at lower then 5" of vaccume so that causes my poor gas milage. could i just plug the pvc connection on the carb and let the valves breath though the cover hole or does it have to be connected? im just trying to iscolate the problem. thanks for stickin with me on this one.

sounds like it is time to hook up a vacuum guage and see what is happening.
I had a relatively new carb do something like this once. It sucked in some dirt from the tank into the carb and the floats were all messed up and wouldn't close. Replaced the cheesy fuel filter the guy before me put on the car and tore the carb apart. Things improved after that.

ok checked vaccume and everything is normal.. idles at 19 in park and 16 in gear. vaccume gauge reads fine during accelleration how vaccume drops and then goes back up. and then how vaccume goes high when the engine is slowing back to idle. anything else i should try to check.

Sounds like an egr valve problem, but I don't know if you even have an egr valve. What carb is on it?

i have an edelbrock 600 cfm mech sec. elec choke.

What distributor is in it?

i have a stock motocraft dist. with magnetic pickup..


anyway i fixed the problem.. i think it was because of my msd box. pulled it out and now the problem is gone.. either the box or my tach didnt work with it. thanks guys for helpin me out.