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I just changed the timing belt on my 01 Civic LX and after idling for a few minutes with no problems it suddenly started running really rough. I've since tried to start it up again several times and sometimes it will start and run extremely rough and other times it won't start at all. The check engine light is not on and there aren't any trouble codes showing up. I'm really frustrated as I just put it all back together and thought all was well but now it obviously needs tweaked. What would cause it to go from running great to having serious problems? Hopefully someone has the answer out there.

 
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Um, the belt was not tensioned properly and after the first few minutes of running, it skipped a tooth causing the timing to be off. This would be my best guess. It definitely sounds like something time related.

 
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i would agree with that, i would recheck timing and the timing belt tensioner

 
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Well, I really wanted it to be something else (something requiring much less work) but since everyone told me that the belt probably slipped I decided to take it all apart again. And what do you know? The belt had slipped a couple teeth! You guys were right. So, I took it off and put it on again, being very careful to get the tension properly set, and it has been running fine for me now. Thanks for the help.

However, I have a new problem now that I haven't been able to find an answer to in my browsing. I replaced the water pump during the belt change, which required me to drain all the coolant. So, I filled it up after that but I don't have consistent heat anymore. It takes a while before my heat gets warm and even then it fluctuates between hot, warm and cold. I always thought this meant that there wasn't enough coolant in the system but I just checked the reservoir and the levels are where they should be. Any ideas on what my problem is?

 
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i would agree to what lemmiehill said cause i had a friend that had the same problem

 
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you need to bleed out the air from cooling system. with car cold, open the radiator cap and start the car. gradually warm the engine by revving upto 3k rpms. once its at temp, turn heater full blast and watch for air bubbles coming from the radiator. keep adding coolant to keep it visible near the top. after 5-10 mins the air should stop. you can also turn the a/c on and do it again. once the bubbles stop, shut off the car and put the cap back on.

 
Rep Power: 214

Ha I knew that was it! At least you got lucky and didnt skip so many teeth as to where it would have had a piston hit a valve. As far as the coolant fluctuation, try what gearbox said and get back to us. Glad to help. Hey, just outta curiosity, im about to do my timing belt, you did yourself correct? How long did it take you and how experienced are you with cars? Thanks for the info,.