Chevy frustrating me

I did remove the air pollution pump and the plastic opening is just open would that prevent it from starting?

Gumby22

Did you verify the new IAC is operating properly? Use the same test as the old one.

I’m not sure which opening you’re referring to but if it’s connected to the intake manifold, block it off to be sure. Most air pump systems utilize valves to control the direction of air flow but if the valves are stuck in the wrong position, it could be allowing excess air into the intake manifold which will affect the ECM’s ability to properly adjust the air/fuel mix.

It may help narrow down the cause of the problem to perform a cranking vacuum test. Unplug the injectors so it’s not just dumping fuel, then find a vacuum port to connect a gauge - the brake booster line is usually the best choice as it’s directly connected to the manifold, but the EVAP purge line port (bottom center of TB) will also work. Have a helper turn the key as you watch the vacuum gauge - it should be pulling 3-5 in*Hg of vacuum during cranking. Less than that and I’d start looking at the exhaust for restrictions. If the exhaust is OK, compression testing would be next.

Chevy frustrating me

The iac isn't moving even with the new iac.

Chevy frustrating me

The oxygen sensor on driverside manifold has the wire broke off. I was going to solder it incase that could effect iac.

Gumby22

Connect a test light between the control circuits of the engine harness at the IAC valve. If you’re looking straight at the IAC connector with it unplugged, the layout is as follows:

[TAB]
A B
C D

The control circuits are separated A to B and C to D - cycling the key on and off will tell you if one or both circuits are down. If the circuits are in tact the test light should come on. If not you’ll have to check each circuit to ground.

The oxygen sensor doesn’t affect IAC position - all it does is “report” the oxygen content of the exhaust so the ECM can adjust the air fuel mixture. Even then, the ECM doesn’t allow O2 sensor readings to affect the air fuel mixture until it’s in closed loop which is about 30 seconds after the engine starts.

Chevy frustrating me

The test light lit up from a-b and also from c-d. When shut off the light would go away in about 5 seconds on each circuit.

Gumby22

Not sure on the IAC if both control circuits are working - it’s not impossible new parts to be bad out of the box, but in my experience (buying parts every day for customer work) it’s not as common as people tend to think. Did it move at all, or did it set its initial position after installation and just hasn’t moved since? If the latter, it may not be moving because the ECM is content with its position.

What about the IAC passages? Are they clean?

Moving on, I need some clarification on some things that have already been mentioned. I read this thread over again and I don’t think this specific info was stated, but maybe I just missed it again.

1) Are you seeing the injectors actually spraying fuel into the TB while cranking? If not, bypass the fuel pump relay by unplugging it and jumper the pink/black wire to battery positive (recommend fused jumper), then try cranking.

2) Did you test for spark at the coil or at the cap/plug wires? It’s possible the spark isn’t getting past the cap.

Chevy frustrating me

I assume that is the bore for iac and I can see it much better then this pic with more angle and nothing is moving

Chevy frustrating me

I suspect the connector for iac could be bad as well but thats a maybe so can I test it out of truck to see if it moves? I will clean the passage as well.

1)yes they spray fuel on crank.

2)I tested with a spark plug tester that flashes good while I crank.

Chevy frustrating me

I pulled the driver's side valve cover tonight just to verify valve operation and timing.