TBI 350 running rich

[HuggerCST]

I just finished putting a rebuilt TBI 350 into my 85, and though it runs pretty good, it seems to be rich, burning my eyes, and I'm getting black smoke when I rev it. It also seems to be worse when it's cold. Before installing it I replaced the temp sensors, OP senders, cap, rotor, wires, plugs, fuel pumps fuel filter, FP regulator, but still have the old MAP, EGR stuff, O2 sensor, and distributor. The harness and computer came from a 87, and the chip and injectors from a '90 350 4x4. The engine is rebuilt to factory stock specs. I'm suspecting it's an O2 problem, because 1- It is used, and 2- It is a one wire, and I do have headers. If I change to a 3 wire heated sensor, can anyone recommend a sensor? Or will any 3 wire sensor do? I have not checked the codes yet, but the service engine light is not on. Any ideas?

[HuggerCST]

I checked the codes, and there are none. It is going into closed loop, and switching from rich to lean, though not very consistant, and the temp reading seems to be ok. When cold, it hunts & searches to idle, has a partial throttle hesitation as though it is leaning out, and when it does idle, dies sometimes as though the key is turned off. It is also hard to start when cold. When it is completely warm, it runs pretty good, but still dies once in a while. Suggestions???

[lurch115]

generally when a motor "wanders" at idle is a sign of an intake leak.......but some other things to check first would be.....the "IAC" valve...or idle air control valve....or that MAP sensor.....had one just all of a sudden go bad in a '92 Cavalier i had and made it run really rich and also made the 4 cyl. run like an old 2cylinder Johnny Popper "John Deere"....maybe try swapping the MAP sensor with one that you know is good to test it......the IAC valve alot of times will get alot of carbon buildup on it.....had one of those that i replaced in a parts store parking lot..... *LOL* NEVER DO THAT! changed it there and ran it home with a 1,500rpm idle in an old cop car.....if you replace the IAC valve reset the computer before you drive it anywhere....

[HuggerCST]

I drove it a couple of times, and it has gotten a whole lot better. It runs good now most of the time, but still takes about 3 tries to get it started when cold, and every once in a while will "wander" and die when idleing. Maybe it's just taking the old computer a while to "relearn".

[ChevyTech]

….. I'm suspecting it's an O2 problem, because 1- It is used, and 2- It is a one wire, and I do have headers. If I change to a 3 wire heated sensor, can anyone recommend a sensor? Or will any 3 wire sensor do?……

In my opinion a three wire (Heated) O2 sensor is a must when using headers. I do not have a brand preference on kits for switching to a three wire O2 sensor.

Do not expect a good clean idle until you have the three wire O2 installed. You may find it keeps going into “open loop” ECM operation when idling for more then a minute or two with a one wire O2 sensor.

I drove it a couple of times, and it has gotten a whole lot better. It runs good now most of the time, but still takes about 3 tries to get it started when cold, and every once in a while will "wander" and die when idleing. Maybe it's just taking the old computer a while to "relearn".

Yes, the IAC does not “relearn” or “reset” unless certain conditions are meet. Some TBI systems need a VSS input to do a forced IAC reset.

Is the IAC new?
Did you clean the TBI passages?
Did you get carb cleaner or solvent inside the IAC?
IAC passages can get plugged up with carbon or muck. The IAC units get erratic as they get old and stick. Use care when cleaning the IAC. The IAC should not be cleaned with carburetor cleaner or other harsh chemicals. If the chemicals get down inside the IAC, it will damage it.


You can try this.
Using a watch or timer to make sure you hit the threshold times on step 3 and 4:
1) Disconnect battery for at least ten seconds.
2) Reconnect the battery.
3) Start engine letting it run for five seconds.
4) Turn key off for ten seconds.
5) Then start it and see how it idles.

If you have idle stalling problems, after a three wire sensor is installed, or in “open loop”, the “minimum air rate” may be to low. When the minimum air rate is to low, sometimes the IAC will not be able to compensate enough, before the engine dies.

Always clean the throttle bores just at and below the throttle plates before adjusting the minimum air rate. Also clean the throttle plates especially the bottom side of them.

Do you have a scan tool that can show the IAC count?

The harness and computer came from a 87, and the chip and injectors from a '90 350 4x4.

I am assuming you made sure there are no compatibility issues here.