I have seen this happen also. Usually its a fuel delivery problem due to clogged final chance screen located underneath lpg pressure sensor or clogged filter in lockoff. As MEngr instructed check other sensor reading with either pda, laptop or hand scanner. If lpg pressure remains in range, check final chance filter located benath sensor. If clogged, clean but take care to not contaminate injector holder by letting debris get beyond screen. Screen is held by small clip. Do not damage screen. If pressure falls out then check fuel filter in lpg lockoff. If clean you may have vaporizor going south or the lpg lockoff is dropping out and test should be performed to verify. Remember ALWAYS drain regulator/vaporizor as recommended..

wence;
Remove the cup holder from the dash and uptape the OBD II plug. Using an automotive OBD II handset look at the other engine sensors along with the MAP sensor that you cleaned. If all sensors are reporting good check the LPG fuel pressure for 4,6 - 4.8 psi. When was the fuel filter at the lock - off last changed and when was the fuel filter inside throttle last cleaned. Also has the tar been drained from the vaporizer/regulator at a regular basis. Check to be sure the fuel relay is making with key switch on and not activating only in starting mode. While checking relay also look to be sure the relay mark EGI is making. Check the injector driver for condensation under the plug. Driver is located next to the ECM under the battery.

i clean it and is running ok but the first time i crank it i start ok adn the second time i try it takes a delay but star and runs good and that is what is doing now takes a delay to start

wence;
Look at MAP sensor's readings closely.