Stumbling,Hesitation.....Cant Figure It Out

Alright heres the deal…went drag racing at the track. When i launched i broke 2 axles…car ran fine when i pushed it off the line. The next morning i started it and it runs like crap. Now that i got the axles fixed when i drive it it “stumbles” when at a constant RPM. If i am sitting still and i hold the RPM’s to about 3k…you can hear almost like a popping in my exhaust. Now i made sure that all my vacuum hoses were attached and i noticed a fairly loud Hiss coming from the engine bay. I scoped around and can hear it most predominatly directly in the center of the intake manifold…right over the PGM-FI emblem. When driving at a consistent RPM it will either stumble or start to jerk back and forht as if you were pumping the gas pedal but it does it very rapidly…almost as if its going to stall. At WOT it seems to accelerate fine with maybe only a slight hint of something wrong. Also i installed some Autozone axles temporarily…are stock axles balanced cause these autozone ones seem to make the car shake a lot under hard accelaration. ANY HELP WOULD BE GREATLY APPRECIATED!!!

Have you checked your ECU Codes (under Teg Tips/Engine). Stumbling could be caused by a faulty TPS (throttle position sensor). Replacing it cured a similar problem in my car.

Stock axles have a rubber balancing donut on the shaft between the CV joints. I’ve seen many aftermarket rebuilt axles that omit this piece and the result is annoying highway vibration.

You said you hear a hissing?

You’ve got a vacuum leak, and if it’s making it run that bad, it’s a pretty nasty one. Probably just coincidence that it happened after you snapped an axle, although if you had a bad motor mount, the engine could have jerked hard enough to pull a vacuum line off of something that’s attached to the firewall (brake booster, etc). And yes, the axles should be balanced; the shaking is most likely the engine stumbling (or one of the axles may be crap).

Start by checking the major vacuum lines - namely your PCV and power brake lines, and go from there. Thankfully there’s not a lot of lines on our cars, and if you have the original hood, there’s a nice diagram on the underside of it showing where they all go.

it isnt throwing any codes yet but i read that is there is a hissing coming from the middle of the intake that it could be an intake valve stuck open partially…therefore i am going to go ahead and do a valve adjustment on it today and will let you guys know. I will also check all the vacuum loines going to the manifold once again.

Thanks for the help…i will keep you guys posted.

anyone know what a loud hissing coming from the middle of the IM could be?>??? Cant find a vacuum leak for the life of me