This is on my '89 IROC in the sig...

I was just out checking my transmission fluid level (with the car running, of course), when I decided to pull the throttle a little bit from under the hood. I noticed that when hit the throttle quickly (open, then close quickly), the engine didn't really pick up much. In other words, the throttle-response time wasn't fast enough that the engine speed picked up in time for the throttle to close again. One thing that I noticed, though, was that immediately as I pull the throttle open, and before the engine actually picks up speed, I could hear a brief hiss from the back of the engine. It's a louder hiss if I pull the throttle open quickly, but it's quieter if I open the throttle more slowly.

I'm not too terribly bothered by this, but the hiss that I heard made me think of a vacuum leak. Also, I wonder if the throttle response could be a *little* bit quicker (although it certainly isn't too lagged). Does this sound like something I ought to fix?

Thanks

 

"If it ain't broke... fix it 'till it is."...HMMMM

TTT

 

so true riley.... so true.

I would check it.. it will prob cause problems down the road...

 

Heh... I probably shouldn't have added that quote to my sig until sometime *after* I was done asking questions like these.

Seriously though, I just finished up doing my first ever rebuild on this engine and I'm just trying to get everything all "shinied up" for the new engine. This is only my second car and I never really got to drive it before I did the rebuild, so I'm in a situation where I really don't have anything to compare this to (i.e. I don't always know what's normal and what's not). Hence all of the "is that like it's supposed to be" questions.

Anyway, I definately heard a hiss and figured it might be a vacuum leak. Is there anything specifically that I should check to verify that, or is that just the sound that the EGR valve makes or something?

Thanks again!

 

The "hiss" could be the FPR adjusting to the change in pilot vacuum.

TPI systems normally suffer from a little throttle lag. This can be minimized by adjusting the throttle minimum air position toward the high end of the tolerance, or about 525-550 RPM instead of the specified 400-450 RPM as directed by most repair manuals. This causes more idle air to flow past the throttle plates and maintains some flow there, instead of having to transfer all air flow from the IAC passages to the throttle plates.

 

Right in the middle of my own" first time". I smell what your steppin in brother...check it out..you really shouldnt hear any hiss noises...listen to Vader... Hisssss the Man!..