Hey guys, just joined, hope this is the right board for this sort of thing. Been lurking for some time now, and i finally picked up an 89 305 TBI Auto Firebird last weekend for just a couple grand and it's a damn nice car for the price but it did not come without issues. It drives and shifts well for the mileage but according to the previous owner it has absolutely refused to run right for the last 6-8 months, if i remember correctly.
(High idle around 1400 RPMs which i know he changed manually with the screw but upon turning it down i've discovered it doesnt really want to run below >700 RPM. If the idle is set below 1100 it won't start easily either)
It's had a bunch of new parts and sensors put on it before i bought it but none of them seemed to fix the issue. As not to make this too long ill try and list all the new stuff and possible failure points.

So far it has
-New TBI Gaskets
-New IAC
-Plugs and wires
-Injectors
-Tensioner, Alternator and drive belt
-Couple other misc unrelated things

That's just what the previous owner did to it, so far all i've done is throw a new TPS on it which improved the idle marginally but it's still rough. PO said he thought it was either TPS or distributor was bad but i'd like to at least try to narrow it down before i throw more parts at it.
So, failure points. The PO did some kind of sketchy smog and EGR delete, crimped all the metal lines and removed the cat and O2 sensors for a cherry bomb, and didn't hook all the vacuum lines back up, which i recently discovered. sorted that out and it went down about 90-120 rpm but once again, still has not fixed the issue. Also, when put in gear the car will drop like 500 rpm and if i set the idle to around 900 manually it'll stall in drive or reverse.
secondly, (if i'm reading them right) in diagnostics mode the car is throwing code 22, 23, and 44. At the moment can't think of anything else, will update if I do.

Much obliged if yall can help. Have a feeling the disconnected EGR and lack of other components might be the culprit but i haven't been able to track down the parts yet, and i'm sure all that will leave me with a dusty wallet considering i have to get a new exhaust welded up too lol. (Unless i get a block off plate and an ALDL cable, but i won't lie i have no clue how to tune a car and i'd prefer to keep it stock ish too til i have the cash for a 350 swap
PS Car will rev alright, sounds a bit sad at lower rpm but very nice in the high range, doesn't stumble either when you get on the gas. Pretty slow too but i think that's just the classic 305


(I've been on here looking at different threads pretty much 24/7 trying to figure it out but nothing was specific enough so i'm posting finally, so please don't yell at me for not using the search function lol)

 

Get a service manual, follow the code 23 trouble tree.
but first you might want to do minimum idle speed adjust if possible with the way it runs and set tps voltage after that if holes are elongating in tps.
egr code would be 32 not necessarily a bad egr valve.

 

Sounds like a class A hack job.

First thing first is you need an 02 sensor. This is a closed loop system and without it the ECM is not doing its job. There is no idle screw on the TBI unit in the traditional sense but you can jack around with the TPS. It is handled through the ECM. Make sure all vacuum lines are connected and or plugged (EGR). Don't throw parts at it until you can make sure everything is hooked up correctly. Likewise, I would check the base timing as I am sure the previous owner did not set it with the EST unplugged. At the minimum you need to get an 02 sensor installed.

 

welp that's something i've just learned about. i have also messed around with the low idle screw and i did not do anything witht the est
quick question, did a forum search but i just came up with acronyms; what is the EST exactly? all i can find is that it has something to do with timing or advancing timing

 

EST = Electronic Spark Timing. Computer-controlled spark advance. Involves feedback from a knock sensor which works to retard timing.

As said, you need to replace the missing O2 sensor, and either get the EGR functioning or get it disabled in a custom tune. Lack of EGR leads to excessive knock-sensor activity, which leads to retarded timing, which leads to shytty performance and poor fuel economy. Yes, you need to check and adjust base timing as needed.

Verify fuel pressure. How old is the fuel filter?

Put the base idle screw back where it belongs. EVERY time someone dicks with the base idle screw, there's no end of idle problems until it's set right again.

Connect a scan tool, find out what the computer is trying to tell you about the engine performance problems. Verify EVERY sensor and computer output. "Codes" can be helpful. The REAL diagnostic power is in the data stream and bi-directional control.

How old are the cap and rotor? While they're off for inspection/replacement, LOOK at the magnet near the pickup coil. Common as dirt for the magnet to be cracked, generally through the rivet area. Causes weak ignition signal, leads to driveability issues including stalling. If your magnet is cracked, you'll either need a new distributor, or a new mainshaft for your existing distributor. "I" would rather put a mainshaft in a used-but-usable Genuine GM distributor housing, than pay half as much for a crappy Communist distributor assembly with a junk module.

 

I see. thanks for the info hoss. turns out i'm an idiot it does have an o2 sensor that may have been replaced recently (or within the last few years that is) for some reason i had figured it would be a short ways ahead of the now nonexistant cat but a another quick clutch forum search turns out its on the drivers manifold.
Negative on the fuel filter, no clue last time that was replaced. i'll add that to my next rockauto order lol

will be checking the distributor tomorrow the cap does not look old but i have not opened it up yet so i'll get back to you on that one
is around 850 rpm the factory base idle speed? it's set around 1100 right now, last owner had it at like 1350-1450 and the protective bolt cover thingamabob was already knocked out

 

That's good news that you found the O2 sensor is still intact. That will make things easier for you. I am not sure what stock idle was but 850 seems a touch too high. before you adjust it further, check the base timing and make sure its at 0 deg.

 

One thing about the '8746/'7747 TBI ECMs is that they don't have any real idle RPM control until the engine is up to temperature. And that is with a 195° thermostat.

RBob.

 

Stock idle in gear should be around 500-525 rpm.

 

What's important in THIS case is not the in-gear idle speeds, it's the base idle set with the IAC not flowing. The base-idle screw was sealed for a reason. Needs to be returned to it's proper position so the throttle blades are appropriately shut.

Then, the additional air for regulated idle speed comes from the IAC, controlled by the computer.

The base idle speed setting should be listed in the service manual.

 

Finally stopped raining. Checked the distributor and cap today for things mentioned above and uhh




Now correct me if im wrong, yall. But it does not look like the pictures above. And if you search up a 305 tbi distributor on google it doesn't match up with that either...

Just a teeny tiny bit rusty too. Lol
Looks like i might have found the problem

 

It’s a cardone reman, replace the cap and rotor and move on

 

I would check that IAC setup. I remember having to short something out. And set it while it was in drive or something like that. If I remember correctly it's not something you just change.
Is it stock ECM or does it have a chip that's been changed?