My 1996 Explorer sometimes will not start when warm. After sitting a while it starts. It stumbles and stumbles and them catches and runs good with a little miss. After it starts it will run at highway speeds and performs ok. i noticed the other day that it needs a muffler. I do not think that has anything to do with the starting though. Is the problem in the computer or the fuel sustems?

The first thing you do is read the OBD2 fault codes and check the fuel pressure when it fails to start.

Fuel can be a problem. There is a system called the "cold start sequence". This is an electronic solution to the old choke system. This system is triggered by the water temperature sensor. If the water temperature sensor is stuck on a warm mode, the engine will not have a choke.

You might change the fuel filter and check the fuel pressure. Check battery voltage too as sometimes weak voltage will make for misfires and as the alternator creates more juice the engine runs better.

Do You Have An engine light on ?
sounds like a dirty or stuck EGR, could use a little better discription plz

Without input from the O2's, the engine goes into fail-safe mode and runs in a full rich fuel trim. When the engine is cold the spark plugs are being "loaded up" with unburnt fuel, and engine stumbles. Hope this helps.

I had this same problem,It was the IAC valve,cost at AutoZone was 48.00 works great now

Possibly catalyst converter on exhaust.

try checking your egr valve pressure sensor i have a 96 eddie bauer explorer and had the same problem and only showed me a code for a oxygen sensor malfuntion and replaced both and it cured it

This may be the early sign of a blown head or gasket. Check your coolant to make sure it doesn't have oil in it or appear to be oily. This is the first thing that I would check.

Fuel pressure regulator leaking . Pull the vacuum hose an see if fuel drips out . Buick Driveability Testing Diagnosis 1996

Watch these series of buick training videos !

fuel pump