97 xj wont stay on

1997 cherokee sport 220k miles. I crank and it won't start, I tap the gas pedal while cranking and it starts but will not remain on. If I hold pressure on the gas pedal and it stays on, I let go and it dies. I tested the throttle position sensor and pin 1 to ground = 60 ohms, pin 2 had 0.7 volts and voltage increased smoothly to 4 volts while opening the throttle valve. pin 3 had 4.7 volts. It appears that the TPS is working corrctly and there might be a problem with the circuit to the PCM (Powertrain control Module) or the PCM itself. Symptoms prior to this behavior are: 1) Evap canister purge solenoid has been chattering. 2) When I tried starting the engine I heard the starter engage, but didn't have enough battery power to turn the engine. I return the key to off, re-engage the starter and the engine turns and starts. I drove home and no problem, I shut the engine off and the symptoms begin all over again. The alternator was tested and is working properly, the battery is also in good condition. Any ideas will be appreciated.

Your IAC is faulty. ( Idle Air Control valve) Opening the throttle is allowing air in, thus starting the engine, but killing it as soon as you let off the gas, cutting the air flow. some times you can tap the valve and it will work.

During the past few weeks I've notice the fuel mileage has reduced to about half of what it was, taking into account what you stated about the IAC, the intermittent operation of the purge solenoid valve, both of these units are controlled by the PCM. Do you think the PCM is dying. Is there any way of testing the PCM without swapping it out??

Usually the PCM is the last thing that should be replaced. Do you have an engine light on? If so what codes? It sounds like there are 2 problems here. The IAC will not nessacarily set a code(at least not on fords) just raise heck when they go bad. I would R&R the iac, then have the EVAP system tested at the dealer. THey put it on the computer and run 2 tests, 1 checks all the electrical, the other checks the function with pressures and hold times. I think this is better then throwing $$ you don't have away in parts you might not need. At least you'll find out the problem. ( that is if the dealer service dept knows what the heck they are doing, instead of snowballing you with bs).

No engine light right now, but it did come on when all the problems started, but it's turned off that same day. I'll stop by the dealer tomorrow.