So on my way home one night the Camaro starts driving real funny. Try to take off from a stop and it stumbles, almost stalls, then catch and take off. The next day I start it up and the idle is surging. Idles about 1500, then drops and almost stalls, then goes back up to 1500. The idle smooths out after it warms up, but it still doesn't drive right. I can also hear a loud sucking noise coming from the TBI. This noise varies as the idle changes. It seems to me that the IAC is going crazy. There are no codes after I replaced the CTS (had a code 15, CTS voltage too high). Right now I am thinking it might be the ECM. I'm running out of ideas there, anyone have any suggestions?

Parts I've replaced:
EGR
EGR Solenoid
CTS
IAC

My Car:
92 RS 305 TBI w/ 5 speed

 

Could be a vacuum leak. Start the car and spray some carb cleaner around the vacuum lines, throttle body and intake gaskets. If the idle changes, you've found the leak.

 

Didn't find any vacuum leaks. Since none of the electrical parts have made any different, I am beginning to think it might be fuel. I bought a fuel pressure tester from autozone, the one that goes inline with the fuel filter. Pressue read 8 psi. It drops a little when revved. Manual says 9-13 is normal, but 8 seems close enough to me. Is 8 psi good enough or my fuel pump bad?

 

I made a couple of videos. Quality is not very good but you can hear what it is doing:
http://www.youtube.com/watch?v=2w3mPdMXIi0
http://www.youtube.com/watch?v=GIvZA-Ylwck

 

Man my 92 does the exact same thing. Once you throttle it for a little while it clears up but it only does it some times. I replaced all the wires,plugs,entire distributor, egr valve, IAC, I mean a ton of stuff and it still does it, the only thing I didn't do was check my fuel pressure. So that would be my guess as to what it is haha

 

My fuel pressure is good, at least just after the filter. It might be on the low side, but should be fine for stock. My car isn't really driveable, it has a huge hesitation when you try and take off.

 

Well, since you have the air cleaner assembly fully off and you're hearing a sucking noise, I'd bet that you didn't plug up the THERMAC port. That's probably the source of the noise.

I have a similar problem with my '89 'bird: she idles rough and stumbles/stalls after driving for a few minutes. It started after I did a LOT of part-replacing due to an emissions-test failure. My fuel pressure is a little on the low side too (8-10 psi), I wonder if the fuel pump didn't like sitting for a month with a nearly empty tank while I worked on the car. The fuel injectors spray fine at all RPMs so I doubt it's the problem though.
Anyway, here's my final part replacement list, which was originally much smaller:
Distributor coil
Distributor cap
Distributor rotor
Distributor module
Distributor pick-up coil
Spark plug wires
Spark plugs
Fuel filter
O2 sensor
IAC
Coolant sensor (the one that goes on top of the engine)
ECU (but not the PROM)
EGR valve
Various vacuum hoses
Air filter
Fuel injectors
Cat
And probably some other stuff I forgot about.

I recently bought an ALDL cable so that I can live-scan the ECU. If nothing appears wrong, I'm admitting defeat and it's going to a mechanic. I'm at my wits end . At least I learned a lot along the way...

 

Well, I finally figured out it was the fuel pump. 8 psi is not good enough.

Also, changing the fuel pump really is a pain in the ***!

 

...and apparently my problem was due to a faulty harmonic balancer. After I got that fixed it ran smoothly, well as smoothly as it previously did , and it passed emissions with flying colors.

Never would have figured that out on my own, that's for sure! It makes total sense, but I don't understand how or why it broke after sitting for a month. Weird.

 

I am having the same problem and have replaced the egr and oil pressure sending unit and tested a whole bunch of stuff but nothing else is coming to mind but the computer or a vacuum leak but im going to look at the fuel pump i hope it works

 

Btw, how do you test the fuel pressure ?

 

my 92 rs 305 is doing the same thing. i've replaced the fuel pump, iac, tps, cts, and gave it a complete tune up, plugs, wires, cap, rotor,etc. it has a surging, high idle that flucuates from 2000 to about 1400 rpms.

 

check your timing. Did you set the tps when you changed it, or just install it?

 

no i haven' checked the timing yet, nor did i set the tps. as far as i could tell, there was no adjustment to it, as the mounting holes aren't slotted, so i didn't put a meter on it. i'll tdc it tomorrow, and check the timing. one thing i didn't mention, was that i put a rebuild kit in the throttle body about a month ago. new regulator, injectors, gaskets etc.

 

What was the conclusion?

 

I fixed mine by doing an LS1 swap

 

Haha thats one way to do it