Intermittent stalling immediately after starting or punching gas
There is gas, the starter is fine, the battery is good. It doesn't matter what temperature the engine is or how long between starts but if I rev up the engine while cranking it starts okay. Rarely I have to rev at stops or the idle drops too low and stalls. If I punch the gas very quickly it revs and drops quickly and then stalls. Starting has a success rate of about 50% without revving. If it stalls, I must rev the engine to start.
If you feel that the fuel pump has failed, then this is the proper way of diagnosing the problem before replacing an item that may not be needed. Starting from the basics, take off the fuel cap and listen closely for the fuel pump to come on as a helper turns on the ignition key. The pump runs for only 2 seconds at a time when the engine is not running. The computer shuts the power off to the pump if it does not see a signal from the crankshaft sensor.
Have the helper turn on the key for 3 seconds and off for 5 seconds and on again a couple of times. If the pump cannot be heard, then replace the cap and lift the hood. Check to see if the fuse to the fuel pump is good. If so, then look to see if fuel is the problem by removing the cap on the Schrader valve on the fuel rail on top of the injectors. Take a small screwdriver and push in on the Schrader to see if fuel comes out in force. If not, hold the Schrader in and have the helper turn the key on. Be ready to release the Schrader if there is fuel pressure, for it will come out fairly steady. If there is no pressure, replace the cap and check the relay. Remove the relay and test the terminals that it was plugged into for power with the key off. There should be one terminal with power. If not, there is a bad wire under the fuse block to the battery; it should have constant power at one terminal.
Take off the air cleaner and hold the throttle plate open with your hand. Spray some carburetor cleaner into the throttle body. Try to start the car for 2 seconds. If it starts, the fuel pump is the problem. If not, the engine should be checked for spark. It could be a sensor or computer-related problem. To be absolutely sure, raise and support the back of the Jeep on jack stands, unless the height allows you to crawl under the back without raising it. Unplug the fuel pump connector at the back of the fuel tank. It will be easy to find and has four wires in the connector. Use a circuit tester and test the harness side for power as your helper turns the key on and off. Remember that there will be power for only 2 seconds, so have your helper cycle the key on and off as you check the terminals, allowing 5 seconds between cycling for the computer to reset. If there is power, the fuel pump took a dump and needs to be replaced. If there is no power, there is an open in the harness to the pump from the fuse block.
Let us know your results and we can go further.
start with the obvious.... any check engine light codes?
from there is to determine if this is an electrical issue or mechanical issue. using a fuel pressure gauge on the fuel rail can tel you if the fuel pump is not supplying enough fuel pressure. if thats fine, then check for vacumm leaks. how old is the jeep? older ones rely a lot on O2 sensor for the proper idle and if the sensor is bad, it can cause the described symptoms.
if all that is good, then do a compression test and a leakdown test. that will tell you if you have any mechanical issues with the engine.
cars only need air/fuel/spark.
I had a similar issue after I swapped the intake manifold & power steering pump from a 1999 Jeep to my '95. When accelerating quickly (onto the freeway for instance) it would stall. I would pull over and it would restart fine. After sticking my head back under the hood, I figured it out: Since the intake manifold was different, the vacuum fittings were different also. When I checked the engine codes, it was giving an error about the MAP sensor input. One of the vacuum hoses were not tight. I also found that the vacuum line going to the FPR at the front of the engine was contributing so I took it off and all has been well since then.
Bottom line: troubleshoot your vacuum lines and the things they connect to/from. If it's stalling when you punch the gas, it points to fuel pressure but your symptoms also point to a vacuum leak.
Sounds like John Hanks is right, throttle position sensor.... take out the sensor or get access to it by removing the intake so you can see down into the throttle body.......and clean the heck out of it. If the problem is better (rough idle or low idle), safe bet the throttle position sensor is the issue and they are easy to replace..... if you know someone that has one, you can also hook up one of those diagnostic computers and tell it (the jeeps computer) to raise the idle speed, if it won't do it = throttle position sensor is to blame........ I have one of these jeeps, and the crank position sensors can go bad too, fairly common actually......h
I have run into this prob many times if you have cleaned the throttle plate
Well you may want to try my fix.
I'm a 28 year mechanic and repair this problem on many jeeps, fords,
Chevys ect.. What you can do is drill a small hole in the throttle plate
About 1/8 - inch be careful pu a rag or towel to catch shavings. Put the breather assembly back on and test drive to relearn computer .
Problem should be solved. I also have noticed lots of the newer
Models of cars and trucks already have the hole drilled. Good luck