joshhsi

I dropped a 305 TBI from a 92 RS into my 91 Z28 a few years back and ever since, it has had a high idle. When first starting the engine, it idles around 2,500 RPM. Once the engine warms up it will kick down to around 1,000-1,500 RPM. This still seams a bit high to me. I replaced the IAC Valve and checked all the vacuum lines for leaks. Any suggestions?

grygost

Throttle position. Check and see if you have the ability to adjust it.

SKELITOR117

iTrader: (3)

I've got the same exact problem.

grygost

Ok, TBI is no idle adjustment but what controls it would also be the IAC. Check the IAC out and make sure it is working, also vacuum leaks cause a high idle as well. Disconnect the battery for a bit then reconnect and see where the idle is. if its still high also check the TBI gasket where the manifold is. Spray starter fluid around the base and see if the idle rises. If it does theres a leak.

Standing in front of the your engine, it's on the left front side of the TBI, will have some wires plugged into the end, has a hex on the end about 1" or so diameter, but it would be metric. A large Crescent wrench will fit.

After you pull the IAC, use a light to check inside the port for carbon chunks. (shop vac is great to pull loose carbon out)

Your idle should be near 1500 rpm with the IAC removed, just a real fast idle.

Then cover the inner port with a finger, the idle should drop to normal if the IAC or it's circuitry is the problem.

nickfrmtx89

i have the same problem on my 92 RS w/ a 305 TBI. turns out my tachometer is off about 500-1000 RPM's over and if you read some of the threads on here thats a common problem for these old 3rd gens.

joshhsi

I found some info online about jumping the A and B pin to reset the IAC, then unplug the electrical connector and use the idle screw on the side of the throttle body to lower the idle. I turned the darn screw until it just about came out of its hole and got the rpm's to come down to about 1000 with a hot engine. I have a newer IAC in, but I guess I can check for carbon buildup inside and try to check the TPS again. If those are all ok....I guess I have a vacuum leak somewhere then.

joshhsi

It's not the tach. I did have the problem with the tach reading double a while back, but replaced the little circuit board and that fixed it.

nickfrmtx89

where did you find the circuit board?

joshhsi

I found a complete guage assembly for sale on craigslist. There is a small board for the speedo and one for the tach as well.

SKELITOR117

iTrader: (3)

I removed the IAC and my car tryed to go full throtle.

xstang77

i had the same problem on my 305 changed iac as well discovered it was the ECT sensor causing the car to not go into closed loop my idle was around 1500 too checked the ect and i could swivel the connector changed the ect and it idles perfect now

1989blueirocz

I have the same problem, when my camaro gets to about 1/4th tank it idles at about 2,000 rpms but if I fill it up the idle is about 600-750. what would make it do that? Someone told me that wwhen the tank gets low there could be a spot where it's sucking air?