I have a 90 chevy blazer with a 5.7 tbi engine, when its cold there is a miss at idle, ive done a tune up and it helped some, but didn`t fix the problem. the other day when I was looking things over, I noticed that every time I would give it some gas the egr valve would open and then close once the engine went back to idle, is this normal ?, im thinking its not and that the solinoid that is controled by the computer to send vacuum to the egr is bad. am I right, or is this normal ?.