Code 35?

[Taker442]

I have a 1994 k3500 truck that is coming up with a code 35.
It has a 454 tbi in it. I also have the shop manuals for it.
The code 35 is the idle valve. The valve has been replaced. The diagnostics in the manual state to check the wiring. In the manual it shows a 2 wire valve. Mine has 4 wires? The wiring diagram I have found for it shows the 4 wires all go back to the ecm.
Not sure what to test?
If any has had this issue and could maybe shed some light on it, that would be great.

Thanks

 

[df2x4]

When you say "shop manuals" are you referring to the GM factory service manuals or something third part like Chilton or Haynes? If it's the latter, I would check the GM manuals. They can be downloaded for your '94 in PDF format from this thread for free.

https://www.gmt400.com/threads/88-95-service-manuals.43575/

 

[PlayingWithTBI]

In the manual it shows a 2 wire valve. Mine has 4 wires? The wiring diagram I have found for it shows the 4 wires all go back to the ecm.

Yes, the IAC (Idle Air Control) valve is adjusted by a 4 wire stepper motor controlled by the ECM/PCM. The more steps commanded, the more the valve is opened to allow more air in thus, increasing idle RPM. As @df2x4 posted, you can look it up in those manuals for your specific year.

Here's a somewhat simplified schematic from an 88 but s/b similar.

You must be registered for see images attach

 

[1997]

Code 35 has quite a list of causes:
- Wiring, IAC valve, intake system leaking, fuel system, PCV valve, A/C system, mechanical fault, ECM

doesn't look like its gunna be a quick fix, i would start with the easiest and refer to manuals DF2 posted, work my way thru.

 

[Schurkey]

Connect a scan tool, find out if the IAC can control the idle.

At minimum, you should have normal curb idle, and "limp home" fast idle, selectable with the scan tool. If the IAC has control of the idle speed, the wiring, the IAC, and the ECM should be OK.

MAYBE there's the option on the scan tool to select an idle speed by 50 rpm increments. I've worked on some vehicles that have that option...I don't remember if the TBI is among them.

There should be a complete diagnostic "trouble tree" for Code 35 in the service manual.

 

[udidwht]

I had a code 35 issue that was very very intermittent. I could go 1000+ miles without one and then...always showed when coming to a stop then moving selector to 'Park'. SES would come on.

I changed the IAC with (2) different makes of IAC valves and same results. Even rebuilt the TBI and new base gasket. What finally resolved it? By purchasing an AC Delco IAC. I've now logged 3,000+ miles and no more code 35 (SES light).