Got an 88 IROC-Z, TPI 350 of course...no power adders just a simple flowmaster cat-back, bought the car 3 months ago. It runs STRONG but it has some problems that im trying to get rid of. First off at idle, if you give it a quick shot...she'll hesitate for about a half-second and then it'll kick in, makes some kind of a hissing/sucking noise like there's a leak or an air shortage somewhere. Second thing is there's a vibration coming when the car's RPM reaches about 3.5rpms, it even does it in park, and it gets worse as they go up. The vibration seems like its coming from up in front of me/below the shifter. Those are the two main problems i've been dealing with, so far i've changed the plugs, wires, distributor cap, rotated the cap, changed the tranny-mount to a prothane (tried to fix vib.), changed the rear because the 3:27 was tired to a 3:73 posi, messed with the timing for countless hours. Now the only thing i havent tried is changing the sensors which i do not want to dive into without seeing what people have to say on here. I'm starting to look down on the TPI era however, i understand they're strong engines when running right. Any help appreciated Thank You!

 

the hesitation and sucking sound makes me think you have a vacuum leak somewhere and also sounds like it's running a little lean. now as far as the vibrations i'd check the motor mounts on that. could be that they're fixing to go. my first camaro with the 3.4 did that before the motor mounts went.

 

that's exactly what i thought!

vacuum leaks suckk

 

As far as the vibration, i'd check the torque convertor bolts, in my formy, they used to work themselves loose once in a while.

 

haha yeah literally. And the torque converter is a possibility. I didn't think about that since it's been quite a while since i've done a lot with an automatic.

 

If you find that the torque converter bolts are tight, unbolt the converter from the flexplate. Start the car and rev it to your "vibrating" rpm. If the vibration is gone then you know that it's after the engine. i.e. converter screwed or driveshaft out of balance.