iac and code 34

P

ppress79

Member
First, I can't get my idle iac count down below 100. I have done a full iac reset by turning key on for 30 seconds, unplugging iac, starting truck and let run until it is in closed loop then manually set idle stop screw to 650 rpm, turned of truck then reconnected iac. I can find no vac leaks or have an unsteady idle like a vac leak but idles at @ 900. I don't know where to look next.


Second, I have a random code 34 that I see in my data logs. I don't get a cel. I have a map voltage of 1.53 ( 3-bar) with key on engine off. I have followed the service manual troubleshooting guide for code 34 and there is no problem. Should I just ignore this until I get a cel hard fail?

Thanks,
Phil
 
Don W.

Don W.

Stab it and steer it
Re: iac and code 34

OK my friend, you're going at this bass ackwards. The idle stop screw is just that a stop screw. Not an idle speed screw. Plug your IAC in (if not already), have the truck warmed up and adjust the idle stop screw so your IAC counts are down around 30. (The screw and IAC counts work in reverse. Back the screw out to increase, in to decrease IAC counts.) You might be getting a code 34 because your manifold pressure along with the high IAC MIGHT be confusing the ECM. Code 34 is signal voltage low which is high vacuum. OR if either the green or grey wire has a short (even intermittent) it will be a code 34. Also there is a grey wire that goes to the TPS. If that one sees a ground it will set a code 34.
 
IGottaSy

IGottaSy

Active member
Re: iac and code 34

Also, watch your TPS voltage as it will fluctuate while you do this. First get IAC where you need it, THEN adjust TPS.
 
Don W.

Don W.

Stab it and steer it
Re: iac and code 34

Adjustable TPS?? I've never tried to measure TPS voltage at idle while adjusting the throttle for the correct IAC count so don't know if it changes (I don't think it does) but there is no adjustment on the TPS that I know of.

When adjusting the throttle stop for correct IACs I usually bump the throttle to make sure it has returned to where it's gonna be when I drive it.
 
liquidswords88

liquidswords88

I pity da fool
Re: iac and code 34

The tps rezeros everytime the key is cycled. When you turn the throttle blade screw your are in essence moving the tps. The voltage can be watched with whatever data logging software you are using.
 
liquidswords88

liquidswords88

I pity da fool
Re: iac and code 34




That's a really crude picture of what the iac does. The throttle blade only sets the baseline amount of air the enters the engine at closed throttle. The iac passage can only add air to the mixture, not restrict it any more than the throttle blade setting. The iac basically leans out the a/f mixture by letting more air past the throttle blade
 
D

Damian

Member
Re: iac and code 34

If it's at 100, your iac is opening to allow more air in. Screw in the adjustment screw and you will see the iacs drop.
 
dgoodhue

dgoodhue

BuSTeD 4.3
Re: iac and code 34

IGottaSy said:
My truck came with TPS sensor with elongated holes like the one in the link below... so yes, it is adjustable Amazon.com: ACDelco 213-905 GM Original Equipment Throttle Position Sensor Kit with Sensor, Retainers, and Bolts: Automotive
Click to expand...

It is not the original TPS if it has elongate holes. The early TPS were adjustable (for instance the grand national had an adjustable TPS). As mentioned above the ECM re-zero the throttle position to 0%. Your chasing your tail by adjusting the TPS, plus you may be able to put the TPS at voltage the ECM isn't expecting.
 
P

ppress79

Member
Re: iac and code 34

Yes, it was an iMac reset and tps adjustment. It took a couple key cycles after reset for iac to come down but it's all good now.

Phil
 
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