Hello i have a 2002 suburban 4x4 1500 ls 5.3l flex motor , The problem is when i first start it in the morning it will not idle with the heater on turn off the heater it idles fine turn it on and really low rough idle and dies. I checked my fuel pressure when i turn the key it spikes to 60 when running its at 45 when i give it gas goes down to 40. Turn key off and it holds pressure overnight. Any ideas?

 

Might try cleaning up the throttle body and intake.
Also consider cleaning the MAF and checking all battery / alternator connections..

 

pressure is a little low, should have a replaceable fuel filter if I remember right maybe take it off and see if you can blow through it.


Check for codes? intake gaskets/vacuum leaks can cause similar symptoms