Stalling and high idle issues

[Muncie]

Ok, new sensor didn't fix it if anything it's now slightly worse... can you point me towards the spark tables I might have luck with? Touch the gas gently dies instantly stab it it doesn't stumble it just spins the wheels.

[antus]

Can you see what the IAC is doing? How many steps at idle?
Is it opening up on the closed throttle when you have the stalling issue?

Idle slowly ramps up iac to 0 steps.

Are you sure the IAC is working, and are you sure there is no air leak? This is your PCM trying to take air out of the engine, and failing. Either the IAC isnt moveing, or its out of range because too much air is going around the TPS and the IAC and still getting in when its closed. It should stop at about 30 when the TB is set correctly, and you would set the throttle stop by watching this while adjusting until its idling ok at about 30 steps.

[Muncie]

So currently from cold start it starts and sits at 850-900rpm itll sit there happily for about 90 seconds then gradually ramps up to 1400rpm and stays there, at the above lower idle its sitting at 30 ish steps once it rolls up to 1400 rpm its at 0 steps.

If i rev it then it settles at 2000rpm then takes quite a while to drop back to 1400rpm. IAC is Moving have removed it and checked it does run at key on, am on second IAC fitted a new one to rule out that been the issue.

Have also had manifold off 4 times hunting for leaks and replaced all vacuum lines and checked all of those for leaks too.... no dice

[brindo]

Silly question, but is the PCV still connected in the standard configuration? If so, that can be a path around the throttle blade.
I have a vague recollection of there being some different types of IAC and some don’t seal against the seat. LS maybe?

And if you still believe that the IAC is passing, can you get it to zero steps with the engine stopped, the pull the connector and run it up?
If the IAC is closed and isn’t moving, and the TPS isn’t moving then the throttle plate can’t be opening up to cause the rpm rise and it must be a vacuum leak.
Other than that, its really only the brake booster that can have a vacuum leak. You’ve checked everything else.

[Muncie]

Silly question, but is the PCV still connected in the standard configuration? If so, that can be a path around the throttle blade.
I have a vague recollection of there being some different types of IAC and some don’t seal against the seat. LS maybe?

And if you still believe that the IAC is passing, can you get it to zero steps with the engine stopped, the pull the connector and run it up?
If the IAC is closed and isn’t moving, and the TPS isn’t moving then the throttle plate can’t be opening up to cause the rpm rise and it must be a vacuum leak.
Other than that, its really only the brake booster that can have a vacuum leak. You’ve checked everything else.

Hi PCV System is deleted banged a welch plug in the lower half of manifold and capped off the port on passenger side too now vents through AN10 to catch can.

Have tried all ports capped off on manifold too runs exactly the same, i also retraced all my wiring tonight where i lengthened for the manifold reverse is all as it should be, driving me crazy. whole problem came around after swapping on the flipped manifold its not the original wondering if theres a defect in welds that open up slowly as it warms up........ in saying that it can idle so it makes me think its a data problem i've also fitted the Stock PCM back in to rule out any weird model specific wiring issues that potentially could have been the cause.

[antus]

What do your logs say, do you see the airflow increasing on the MAF as the idle goes higher? If its an air leak I'd expect that you dont see that because air is sneaking in around the sensor.
What you say about changing the manifold does raise questions, if it was working before the first question should always be "whats changed?". If you have logs of warmup and idle from before, compare that and a current one.
You could post up a log and see if anyone has the time to look at it and knows enough about what to expect to see.

[Muncie]

bit of resolution here, was a deformed plenum from when it was welded when it was cold it would seal and as soon as it got a bit of warmth in it would twist and leak just enough to completely ruin my day over and over.

i ended up fixing it by just sanding down the surfaces on a sheet of glass and making a more forgiving gasket between plenum and manifold. after that the stalling issue went away too. Its still hard to start but i'm getting to bottom of that too almost there.

[Wade]

HPA academy and even in the Greg banish tuning book both say not to set idle timing at mbt. If idle timing is the same as main spark the car will feel flat. Also with idle timing you want some in reserve so that if the engine goes to die the pcm has that reserve and can compensate. If your already at mbt there’s nothing in reserve

[Wade]

Yeah I was leaning towards vac leak or faulty tps. Glade you sorted it. You spray around the intake and if rpm changes you know you’ve got a vacuum leak. Or just make up a pressure tester or get a smoke machine. Just don’t lend them out, you don’t get them back