OHM testing specs for sensors

[jw_96]

Update: changed oil, drove truck now when I turn on ac it doesn't idk up just stays at where it is maybe 700 rpm maybe even goes down a little.

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[streetperf]

Do you have a scanner?

You can download (Android) DashCommand and the extended GM PIDs for your model to check the TPS. It's maybe $10 for the app and another $20 or so for the extended PIDs

It will show the TPS position as you press the gas pedal with ignition on and engine off. It should smoothly open, the percentage should not jump suddenly.

I don't think you can command the IAC position with it, though. That would probably require the more expensive scanners.




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You can also use a voltmeter, ohm meter will lie to you.

 

[barry_g]

informative thread.
I'd like to revive it...
I have 1996 k1500 manual trans.

I simply swapped mine after verifying it was the culprit to start and stall more than several times at 10F and colder.
I caught it making a loud click, and truck starts perfect afterward..even at 20 below. This was by chance standing at the engine bay.
I knew to get a new IAC.

I bought a new one from ebay 10 bucks.
my stuff is all new, entire fuel system included.
beauitful runtime, outside of the arctic.
even then it always starts eventually. I just do not want to labor an ice cold battery.

I found my factory distance on pintle was out further then the new one.
found on the new one, by turning the pintle, I created the same distance...the shaft itself is not moving, it is specific to the threaded pintle. i finally got it to work, for 750 idle.. and it screamed to 2500 specifically between gear changes. Hitting brake and slowing down, the iac follows it somehow, high idle no longer.
I think it is looking for an automatic transmission.

Nothing cured it. I did all the 10 second stuff.
If I screw that pintle back in to how I got it in the box...it is 1800 idle...never comes down.

I tested my old one, (which works perfectly in toyota tocoma weather).. and found it fails the ohm test on one pair.
I have yet a third iAC on the way. The top brand at rockauto is Delphi...will see how it does.

I am conviced the manual trans needs a special version..and my original has no high idle side of the coil in a functioning state... 27 years original. someone intentionally made that IAC. I am quite certain.
For now, I have my old one back in, sprayed with brake clean and looking better.

I have been after this one last task since 2018.

I am simply after mastering a cold start. the entire engine bay is lit up with new stuff. injection, gas tank, pump.. Just trying to get after details..

Does anyone else have the manual trans mystery IAC problem? I think it is looking for the D for drive in the automatic function.

 

[Schurkey]

Have you verified the wire harness? No IAC is going to work right if the electrical power doesn't get to it.

For that matter, you could have a failed quad driver in the ECM.

This is why a real scan tool is the best diagnostic, and enormously better than an ohmmeter and/or a voltmeter. Find out if the computer can actually control the IAC.

On my '03 Trailblazer, I can pick an idle speed in 50 RPM increments between 800 and 1200 RPM on the scan tool, and see if the engine RPM matches what I've selected. Can't say I've tried that on the K1500 or K2500.

 

[Erik the Awful]

There are few sensors where an ohms check makes sense. The CTS can be ohms checked. The TPS needs to be checked with a scan tool or reading the volts. The crank sensor requires an oscilloscope or a scan tool. The O2 can be checked with a scan tool, an oscilloscope, or reading the volts. The knock sensor can be checked with a scan tool or reading the volts.

The one tool that can do all these checks is a scan tool, and it checks them at the ECM so you eliminate wiring issues between the sensor and ECM.