The car in question is a 1992 Firebird Formula. The engine is a 305 TBI. I just finished a major tune up on it, and have noticed some problems I can't figure out. I think it's a vacuum leak but I don't know where to look. Anyways, here are my symptoms.

- Rough idle when at normal operating temperature. When I start it and it is the process of heating up, under 200 degrees, it's fine. Normal operating temperature for it is usually around 200 or so if I recall correctly. Once it's up to temperature, the idle will jump from 1000 to 250 and everywhere in between. Normally it sits at 500rpms.

- Occasionally, it doesn't happen often, the car will stall when I start it up. It's happened about 3 times in a month, so I'm not too worried. It stalls immediately after starting, then when I try again I just have to hold the key in longer to run the starter for a little longer. Then it starts and runs fine.

- Excessive vibration. Sometimes it's so bad I can see my steering wheel just shaking like it's trying to escape. It's kinda funny, actually >.< Sometimes the vibration will be so bad I can hear wires under the dash banging around. Maybe my harmonic balancer?

- Lack of power. Now I may not be able to judge this correctly due to my inexperience but I am almost positive there's definitely been a lack of power. Not enough to make it feel like I'm in a v6 but I can't remember the last time I was able to peel out.

- An occasional grinding sound. I can't exactly tell where it's coming from but it's somewhere behind the engine I think. I have no clue as to what it could possibly be. I can hear it when I'm just sitting in traffic - I think it only does it when it's at normal operating temp but I'm not quite sure.

Anyways, that's about it. I'm thinking the rough idle and the stalling is caused by a vacuum leak at the gasket of the injectors or the intake manifold. The vibration I'm thinking is the harmonic balancer. I honestly don't know.

 

If you think there's a vacuum leak, a vac. gauge would tell you pretty quick if there is one or not. Could explain issue #1.

Vibration could be related to shot motor mounts.

Try to locate the source of the grinding noise. Towards the front of the car are the driven accessories. They have bearings that can die. Towards the back more are exhaust heat shields that become loose and can rattle around, sounding somewhat like a grinding noise.

 

The grinding noise is between the engine and the dash, towards the bottom of the car. Also, I lack a vacuum gauge and was hoping there'd be a way to check without using one. And are there any other causes of vibration?

Thanks.