Ok my cousin has a 85 firebird transam, 5.0 TPI. we can not get this thing to run decent to save our lives. so far we've done cap, rotor, wires, plugs, MAF. im not gettin any codes but the car just runs like crap, it wont even idle and i cant screw with timing enough to get it to even idle like crap. i can hold the throttle open and get the car to run but once you let out the throttle to closed position it dies. the idle screw is all the way up mind you. ok when i am holding the throttle open while its runnin, i get normal exhaust sound and every 7-15 seconds theres a muffled backfire that comes out. this car is giving me a major headache. fuel pressure is at about 40psi. and other that that i dont know what else to check. oh yeah ive changed the fuel filter too.

Thanks guys hope you could understand some of that

 

350Z,

Yeah, I followed that just fine, but I'm a little deranged, anyway.

The '85 TPIs are a bit different than any of the other years, and the ECMs are not quite as "helpful" as in subsequent years. Still, there should be enough help available to at least get closer to the problem.

The good part is that you've already covered the basics with your cleanup of the ignition system. That's always a good first step so there are no random questions about it.

I'd suggest you bypass the EST and reset the base timing to stock specs just to make sure it is correct.

One thing to bear in mind is that with any year TPI, a sticky IAC sill not set an error code of any kind. It will also potentially cause idle problems as you describe.

Since you didn't specifically mention it, I'd also suggest you thoroughly clean the throttle body, IAC air passages, and remove and clean the IAC. That alone may help some of the problems if not cure them.

Checking the TPS voltage is also a good idea.

All of those items are critical to a proper idle.

 

Along with the above, check for rotted or disconnected vacuum hoses and PCV valve/system.