Hi. I have a 90 tpi in my 71 chevy s/w. I recently changed my IAC unit. The only part avail. at the time was for a 305. The engine doesen't die on decel now , But I've this very loud sucking sound coming from my intake snout.Inhave reset my base idle and the tps, but no change. What is the difference in the 305, & the 350 IAC units.

 

IAC Fitment:

85-92 305 TPI
85-92 350 TPI
89-92 305 TBI

Link to TPIPARTS: http://tpiparts.net/inc/sdetail/360

So you have the correct IAC. Did you screw it correctly, did it have the special little thicker gasket that get flattened when screwed in ?

 

My tpi unit was supposidly off a 350, but I cant say for sure.The Iac didn't come with a gasket so I made one from gasket material. I figures the Iac would adj. itself for proper idle rpm.

 

try spraying starting gas around the IAC on idle to see if you have a leak.
The AC Delco IAC comes with a special gasket to use for proper seal..

IAC adjustment guide: https://www.thirdgen.org/tpimod2

Re-set it and test what I said and get back here

The IAC is the same between 85-92 (TPI/TBI/305/350) so its the correct one. (if it looks like the one on tpiparts I linked to..)

 

I agree, sounds like a leak at the throttle body or IAC somewhere; if you get no leak from there ensure you clean the inside of the port the iac goes into well, I had major drivablility problems (especially idling) when mine was all gunked up....

 

TPI systems are the same al the way up to I think 1989. Im not sure how different they are from the later IROC-Z models.

 

I cleaned the unit before I Installed it. I also installed new gaskets throughout the system.
The noise didn't appear untill I changed the IAC.
Yesterday I ran it for a while, and as the engine warmed, the sucking noise dissappered, and as it got warmer, the noise came back. Then after the comp. went into closed loop, the noise stopped again.
I can wrap my hands around the the snout filter and muffle the sound, so it is diffinetly comming from the front opening. It almost has to be the IAC, because its thr only thing I've changed, The engine rpm does not change at idle wheather its making the noise or not.
I have ordered a gasket set for it, it should be here today.I 'm pretty sure thats not the problem, but at least I will have eliminated one variable

The fact that it goes away when it is at running temp.should eliminate the possibility of a vacume leak from the outside.

Thanks,Morris

 

I got the new gasket set in yesterday,and installed it, but the sucking noise was still there. So today I reset the IAC & the TPS and it dissappered. The gasket I had on it was from a late model compressor,the flat one with the rubber center. Just eyebelling it , it was about twice the thickness as the delco. I guess the comp. couldn't make up the diff. Anyway, thanks for the ideas guy's.

Morris

 

Glad you found your problem

Keep her cruising!