I have a 1990 5.0 w/ a T5. I drive about twice a week. Whenever I start it after it has sat for a couple of days it will fire right up idle for about 5 seconds then it will die, what could it be? After it dies it will crank up and run fine.

 

Try cycling the key a couple of times to pump up the static fuel line pressure before cranking. if that works you are having a leakdown problem, nothing major, just a sign that you'll be needing a fuel pump in the future, leakdown is just in the early stages

 

i have a 1990 also, and if i start it up cold, it dies unless i give it gas but it will run fine when its all warmed up. did you clean the IAC and check the TPS voltage? heres a good site, one of the stickies http://www.muscularmustangs.com/iac.php

 

This is for Blue Oval.

Check your ECT, it effects air/fuel ratios, spark timing, and idle rpm. If the connections are corroded, it will cause higher than normal voltage.

It may not be the problem but bear with me...

If the ECT suddenly signals an infinite resistance the computer ignores the signal which would cause the air/fuel ratio to run rich. A 'Failure Mode Effects Management' or FMEM in the computer switches to a fixed resistance for the ECT allowing a warm engine to operate as a warm engine. As a result dont expect a cold engine to operate properly with a fixed warm FMEM signal.

This is from an 88-93 EEC-IV service manual. ECT voltage reference is listed as 5v.

 

I had the same problem once I bought my 88 I just gave it a little gas when I started it but my first thought was that I may need a new fuel filter so I went and changed it and havent had the problem since then, may want to try it haha for 10 bucks cant hurt right? good luck.

 

thanks guys ill give it a shot