My 2007 colorado will not start on some mornings. my mechanic had it for 2 days and it started fine and said it needs to not start for him to be able to fix.about 2x a week it wont start waiting 20 mins then it usaully starts.

I replaced my computer at 53,000 miles and it starts up OK now with an occasional issue with starting like it has crud in the line or something, but the resetting the key after a miss does require the 15 minute wait. Had to do it once since the computer was replaced, but the issue before was the anti-theft system would shut it down after starting every time requiring a tow truck to get it to the shop. $700 for the computer chip replacement.

If the security light is on, the problem is with the Vehicle AntiTheft system. The key with the chip is not being read in the ignition cylinder. Therefore the computer doesn't allow it to be restarted for 10 minutes.

I am thinking that a battery terminal was loose and the mechanic just tightened it up with out bothering to mention it. Ask as to what was actually done to put your mind at ease.

I had the same problem in the past. A mechanic told me that sometimes the keys become worn and will cause that problem. They made new keys and it worked just fine.

Someone will need to figure out if you are lacking spark to the plugs or fuel to the injectors when it won't start.

try if this works\improves your situation;

turn the key to ON but don't crank, let it sit for 2 seconds. Do this 2-3 times, then put it in the ON position, wait 2 seconds then crank. As for what it is, could be spark plugs, fuel pump\line issue, etc..

It sounds like the starter solenoid is going bad.

Define "won't start." Do you mean the starter motor won't crank the engine? Engine cranks but won't fire up? Fires up but dies?

Put your key in turn it on dont start wait 10mins take key out wait 10seconds repeat 3 times total 30mins. If that dont work try another key

always be sure to change timeing belt as reg. maint. but sounds like ingnition module is getting ready to go