Replaced timing belt on my 99 Breeze and now it runs rough at idle

Vacuum leaks cause a high idle. Why did you replace the timing belt? Did it break? Which engine do you have?

The water pump was leaking so I replaced it and while I was there I replaced the timing belt. I checked and double checked the timing marks. It runs great at highway speeds and when you first start it when the engine is cold.

Sorry its got the 2.4 engine

It has a 2.4 engine

The 2.4L is an interference engine. You should be okay if you put it at top dead center on the compression stroke before you removed the old belt. If you turned any sprocket with the belt removed, it's possible to bend a valve. That can easily not cause a noticeable problem at higher speeds. If the valve leakage isn't real bad, it might not show up with a compression test, but that's still a good place to start. A cylinder leakage test is much more informative but it takes longer and requires a special tester.

I just went out and looked at the engine and on the valve cover it says 2.4 dohc. What does the dohc stand for?

Dual overhead camshafts. That means three sprockets have to have their timing marks lined up when the new belt is installed. Sometimes they can appear to be set properly but one or both can turn a little when the tensioner pulley is tightened. Once the installation is complete, the final step of the procedure is to rotate the crankshaft two complete revolutions in the normal direction, by hand, then recheck the timing marks. Very often you'll find a sprocket is off by a tooth. It happens even to experienced mechanics.

So if it was off a tooth would it do what it is doing running rough at a idle. So what it looks is your telling me I should check the timing again. My repair manual said to line the cam marks and put the crank marks on the leading edge of the tooth. Is that true?

Thanks for the info I will check it out tomorrow.

The service manual procedure makes it sound more complicated than it needs to be. I drew this picture that shows how the cam sprocket timing marks start out being off by a half tooth. That's because they're going to turn a little when the slack is taken up when you release the lock pin in the tensioner pulley. After you do that and turn the crankshaft two revolutions, (clockwise), all three marks should line up perfectly.