I have a 1998 Jeep Grand Cherokee, its the 4.0 straight 6. I replaced the fuel pump, starter, and alternator all within the past 6 months or so. I tried starting it today and it started the first time and then the engine shut off. I tried starting it again and it would crank but it wouldnt start without hitting the accelerator. I didnt mash it down either, just lightly gave it a little gas and it runs the same way it did before this happened and the engine continuosly runs with no problems. The check engine light comes and goes, the code it throws is an 02 sensor but its been replaced and the light still wont stay off.

I replaced the spark plugs, distributor cap and wires 2 or 3 years ago and havent checked the spark plugs yet, I'll probably check them tomorrow.

I noticed recently that when I've been starting it, it hasnt been idling up high like most vehicles do when you first start them and then drop back down to a lower idle. Before this happened it seemed like it was starting kind of weak. The battery is only a year or 2 old.

The first thing I'm gonna try is using the seafoam spray into the throttle body to maybe remove some carbon buildup, its overdue for that anyways, but does anyone else have any ideas or suggestions of what this could be?

 

Idle air control valve?

 

Welcome to CF!

Yes, the IAC was my first guess. It's probably dirty and should be removed and cleaned, both the valve and the port in the throttle body. Remember, there is no fuel in the intake system, just air flow devises that meter and control the air. The fuel is injected into the intake port just before the valve.

I laugh every time I see guys pumping the pedal to try getting more fuel into it while cranking it. It sometimes needs a little more bleed air, but lots of pedal just confuses the computer. If the IAC is working properly, it should start and idle at about 1000 rpm until the PCM starts getting info from it's sensors, then it drops to around 650 to 700 rpm.

Try using a scan tool and clearing the codes.

 

Pull the codes again. Just because you replaced the sensor does not mean it fixed the problem. You can be burned by installing a new sensor and not double checking that it's actually working.

But so far it does sound like symptoms of an IAC not functioning properly but again, let's get some data

 

Your problems are going to continue to get more frequent and worse. That o2 sensor will ultimately cause back fire so bad your muffler will explode.
I changed everything you changed and more. I even changed some things 2 and 3 times with in weeks of each other thinking I just got bad parts.
I called an off road garage by me. The kind that lift vehicles and tires. I asked them who they thought was the best jeep mechanic in town. I found my place.
It turns out this problem your having is coming from a malfunction where the wires meet with your computer.
You need wires repinned and or replaced.
Call a good jeep place or if your good with wires, get out your volt meter