Quote:

Originally Posted by robertmee

is that as simple as removing the connector?

It is on my corvette. But it may or may not set a code you will need to clear.

 

Yup. Start the engine, let it warm up, and the idle settle to where it should be, then unplug the IAC. And yes, it likely will set a code.

 

Okay, so let it warm up. Truck was idling around 890 rpm +- 10/20 rpm. A/F was around 14.8 and then the truck would stumble, and the A/F would jump to 16. Rinse and repeat.

So, I checked the cylinders with the IR gun and they ranged from 500 Deg to 390 deg. I though for sure the one that read 500 Deg was going to be the issue, as that temp indicated running lean.

I hooked up my digital timing gun, I pulled the IAC and started unplugging an injector one at a time, and each and every one dropped the RPM's to 790. Bummer.

I did notice that with the IAC disconnected, the A/F settled at 12.5 rock solid. No more surging lean. Don't know if that means anything to you guys?

Next test will be to don my Arc Flash gloves and start pulling plug wires at the distributor while running and see what the RPM's do.

Any other tests before I tear all the turbo piping out to get to the spark plugs?

 

Quite likely you will see the exact same RPM drop disabling spark, as you did disabling fuel.

 

I figured as much, but since it's fairly simple to do, probably should go for it. The only thing I'm thinking is maybe I have a weak injector, so that at Idle, I'm not seeing the issue as bad. I'd hate to throw parts at it, but it's getting to the point of new injectors and new plugs at least.

 

Just out of idle curiosity..... Have you tried unplugging the O2 sensor, and see if that changes behavior at all?

 

No I havent....but I did plug in my laptop today and monitor the o2....it was cycling 100 to 900mv once in closed loop like one would expect. I do have a spare o2 so I can swap out.

 

Try just unplugging it first. No point in changing it if it isn't the problem.

 

Robert,
When you unplugged the IAC and it went to a solid 12.5, to me, that sounds like the computer went into a limp mode.
That being said, IMO I doubt its ignition or injector.
Does the standalone computer set codes?
Is this a speed density or maf system?

 

The only code set was tps low because I inadvertently unplugged it and 42 o2 lean. It's a MAP set up, so speed density. When I said standalone, I should have been clearer. It's still using the stock ECM but with a custom turbo tweak chip and 60 lb injectors. So, the , TPS, IAT, MAP, etc. are still used to set the fuel curve.