Intermittent starting issues

I've searched, but I'm trying to narrow down the culprit so.... 96 4.0, auto, 231 184k. Over the last year/year and a half I've had an issue with starting. it turns over, but will only stay idling if I give it gas. This lasts maybe 20 seconds at most, then it evens out and is fine. It's not stalling out, and cold/hot has no effect...it happens in all weather and engine temps. I've tried the poor man's pump prime to see if it's fuel pump related, but usually I forget and just step on the gas when it occurs instead of turnign the key a few times to build the pressure up.

Obviously whatever the problem is is something that is on it's way out (I'd think).... I've cleaned the TB, replaced plugs and wires and all standard maintenance. I've also run injector cleaner through it a couple times with no effect.

So I'm thinking.. IAC, NSS, fuel pump, fuel pump relay, fuel filter....... any other ideas? I really want to tackle the problem before it gets to the point of stalling or leaving me stranded somewhere. I've just kept putting it off b/c it hasn't died yet and only happens maybe once a week.

Just unplug the IAC and see if it changes the symptoms.

Will it run without the IAC plugged in?

Yes.

ok so should i just leave it unplugged for a while and see if it acts the same?

Yes. If you don't see any changes in how the engine runs, that is a fairly good indication that the IAC isn't functioning when plugged in.

If there is no change in the operation of the engine don't immediately run out and buy a new IAC, it may just need a good cleaning.

awesome! Thanks for the info!

Ok there is no way mine is running with the iac disconnected. It stalled and would not stay running at all without giving it gas. In fact, to get it running again I had to reset the computer by disconnecting the battery since it still wouldn't idle after I plugged it back in.

If it gets warmer out some day this week I might clean the iac, but I'm not messing with it at the moment.

Sounds simple but be absolutely sure that your battery is up to snuff. A marginal battery can absolutely create the symptoms that you describe. And yes, you can have a battery that is strong enough to start the engine but give you stalling symptoms. In fact, it happens more than you think. Load test your battery to be sure you're not chasing your tail.

Tough to isolate if it straightens out after a few seconds but the throttle position sensor could be in play here. It also wouldn't be a waste of your time to hook a fuel pressure gauge up to the schrader valve on the fuel rail and then monitor pressures as it starts and runs and then straightens out.

Test your way to a solution! Good luck and let us know what you find.

i had an issue somewhat similar on my 93. right after i got it going first thing in the morning, it would sometimes intermittently run rough and occasionally stalled out.

Changed out the fuel filter, ran some lucas oil and was good as gold.

when i pulled my old fuel filter RUST came out of it... so it was beyond past due...

good luck

Thanks for the posts guys! I'll def check the battery as soon as I get a chance, and the fuel filter sounds like a good option too. I'll have to figure out if it's in or outside the tank on the 96 though.