1989 2.8 V6 T5

Hey everyone. Trying to fix codes 33 and 34 that have come back two months after replacing the MAF. Was going to start by adjusting the idle speed, followed by adjusting the TPS voltage. I followed this post for the idle adjustment:
https://www.thirdgen.org/forums/v6/2...rocedures.html

But when I got to step #6, which is start the engine with the IAC connector unplugged, the engine would start and die within a second. Tried this several times with no results. Once I plugged the IAC connecter back in it would run fine. Unplugging the IAC connector with the A and B terminals connected of the ALDL is supposed to park the pintle in place right? Is the IAC bad? Pintle perhaps not moving as it should be? Any help is appreciated!!

 

That fact that the engine will idle with the IAC connected means that the IAC is opening (admitting air) to keep the engine running. A failed IAC would not do that, thus you proved the IAC is working.

Verify the throttle body, throttle plate, and IAC air passages are clean. Open the throttle and inspect the back side of the throttle plate as well. If there is an air bleed hole in the throttle plate, be sure it is not obstructed.

Once all that is clean, warm the engine to full operating temperature, then attempt the idle minimum air adjustment procedure. If the engine will not run, try opening the throttle via the stop screw and attempt the procedure again. You can always back it off later as necessary.

 

Do I even need to adjust the idle speed if its idling okay? It idles at 1000rpm when the engine is warm, could I just go straight to the TPS? i cleaned all of the throttle and IAC passageways when I did a full tune up two months ago.

thanks for the reply!

 

1,000 RPM is probably too high with a fully warmed engine. Asie from that, it should still idle with the IAC disabled, albeit at a lower RPM.

If the throttle body is clean and TPS voltage is close to correct, the final adjustment of the throttle stop screw can be made. This should be set to about 550 in a manual trans vehicle. The TPS can be adjusted if it's out of the acceptable range.

IIRC, the ECM idle learn procedures don't apply to an '89, but you may want to research that to be sure.

 

Unless the IAC stuck open. I just dealt with that a few weeks back. Idle stuck at 1300 but idled at 700 when cold. I couldn't figure out why the idle would climb. Then I stuck my finger over the hole for the IAC and it died. Pulled the motor out and ground the diag terminals and nothing. It didn't move at all.

This was on a 350tpi so it may not apply to the op.

 

That's a good point, but if I understood the OP correctly, the engine would not start/idle with the IAC parked closed and disconnected. That makes me believe the IAC is opening to admit air, and thus is working. When forced closed (jumpering the ALDL) not enough air is admitted, thus the minimum position adjustment of the throttle plate.

 

Lol. I thought about that right after I posted.

 

Lck119,
What type of timing gun are you using ?

What are you using to read RPM ?