Won't idle

[351MAN]

I have a 97 buick century that I install a 96 dohc in. The car won't idle but if i unplug a vacuum line the car will idle fine. Got a code p0172. Checked the fuel regulator, its not leaking fuel. Do I need some type of tuner to reconfigure the computer? Im using the century's computer so trans. will be controlled correctly.

[RedZMonte]

Hmmmmm... do you have the DOHC ECU? if so i would plug that in and see if the car will idle then.... I would suspect somthing else if your unplugging a Vac line, it basicly is bumping up the idle to compensate for the vac leak... Clean the IAC. The IAC is supposed to basicly create a vac leak to adjust the idle (to put it simply). have you let the motor run up to full opperating temp? the DOHC's are notorious for intake gasket leaks.... which could cause a bad idle.. was anything done to the motor before you swaped it in?

P0172 System Too Rich (Bank 1)
A code P0172 may mean that one or more of the following has happened:

The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters can cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
There could be a vacuum leak.
There could be a fuel pressure or delivery problem

[351MAN]

I changed the timing belt and the lower intake gaskets before installing motor. Checked fuel pressure, its 40psi with the vacuum line hooked up and 50 psi with it unhooked. I don't have a dohc ecm. Should I install one to see of that will clear up the idle? Tried a new iac valve. It still does the same thing. Now if I start the car up cold with the vacuum lines hooked up it will run until I rev it up. Then it wont return to idle it just shuts off. I'll check the maf. I also notice my engine doesn't sound as zippy as one that I recently heard in a MC Z34. Is that because of the 3.1 programming. Thanks for the help.

[SappySE107]

The 3.4 DOHC won't run with 3100 tuning. The injector size is different, as well as the spark it will want and the fuel delivery vs MAF as well. You need to run a 97 DOHC computer and then tune it from there if need be for the trans.

[351MAN]

Thanks alot for the help. I'll try to find a 97 ecm. Will I have to changed any of the wiring to different pin locations or are they the same. Thanks again for the help.

[SappySE107]

I only know that the 96 and 97 3100 PCM are compatible without repinning. I know the same is true 96-97 DOHC as well, but between the engines, I am not sure. I would imagine they are the same since it would cost GM less, but I would hate to assume that as well.

[RedZMonte]

if you have access to all data you should be able to see the pin outs for the 2 harnesses. hard to say for sure without seeing the scematics. What engine harness are you running? if your running the DOHC engine harness you shouldnt need to re-pin anything, if you are running the 3100 harness you may need to change pins.

[351MAN]

Found and installed an ecm out of a 97. I'm going to have to repin it. I used a 3100 harness. When I installed the ecm and turn the key on it started on its own without turning it to the start position. Also none of the gauges worked. I do have alldata, so when i get some time im going to repin it. Just wondering though will switching the chip from the dohc computer to the 3100 computer have all the right programming?

[pocket-rocket]

There is no "chip" per se like the OBD1 cars and their MEMCALs. Your OBD2 computers are flash based, so they are re-written through the diagnostics port vs pulling a MEMCAL and reprogramming it.