it will all the sudden not run at low rpm;s but if you hold gas peddle about 3/4 down it will run. then if you drive it fast over 70 mph at the higher rpm it will stop doing its problem. there are no check engine lights on or code. fuel presser is fine. can't fugue out. the why it will do is not run low idle and then after a very fast drive go away still no check engine lights or any thing. HELP!!!!!