Timing belt.

The valve timing will either be advanced or retarded from optimal which will lead to either rough idling or poor fuel economy. Check engine light will usually come on and codes for lean or rich operation may appear or for variable valve timing vehicles there will be codes for intake timing retarded or overly advanced. Worst case scenario in a high performance engine you could actually hit the valves with the pistons as they would still be open when the piston is at TDC. This is unlikely in most production vehicles

Car will idle rough.Engine will probably shake.The more teeth your off,the worse it will run. Uneven results in a compression test. Any car that has an "interference motor" will likely wind up with bent valves,if you use it.

The belt may have slipped or stretched or a tensioner is bad or may have been installed that way. Most times if off by more that one tooth it will not start or run bad or die soon after. The issue is if the engine was running or started when the belt slips too far or breaks then it will (if its an interference engine) damage the valves (at very least) and pistons.

Guys, thanks a lot. I will take it back ti tge machanic and have him double check it. I'll let you guys know. Thanks again.

Need help!!! my car is idleling at 2 and a half RPM when i start the car cold or hot engine, then when i turn on my heater or AC and tge compressor turns on, my car RPM idle goes up and car excelerates on it's own, where i have to press down hard on my brake pedal. Need help.

What car? Was it worked on recently?

Also brake booster uses and can loose vacuum from the engine as-well as the brake booster one-way valve in vacuum line to it, Throttle body may be dirty and not closing all the way, can remove and clean with throttle body cleaner and use a new gasket and do the IAC at same time and use only nylon brushes in assorted sizes.

Have it checked for codes Also IAC can be dirty but also the place it goes into can be dirty.

Thanks, I replaced the IAC with new one and the code are gone. I bought a new throttle gasket and about to fully cleaned the throttle body part. Whats a ECU and EEC and hay, you've giving me 100% possite direction regarding this issue

Thanks. I'll check all u suggested to check and due. Thanks again.

It is the computer.

Your welcome.

So I followed up and found that my throttle body was dirty and that it had a vacuum leak, had it cleaned and it worked temporary, but better than before. Air is still escaping out by the outer throttle wire spring that connects toward the inside throttle body flipper, smoke test done shows it. Those that mean the throttle body is bad completely. Or should I clean it again and should the throttle sensor position hole be cleaned as well, could that probably also be reason why air is escaping from the other side where the spring connection is and keeps it from working properly.

You may need sensors or have them tested and may need some connecting hardware, but either way I would also replace the throttle body or rebuild it.

Thanks but, I thought one couldn't rebuild this throttle body parts, throttle, spring,spring connection, and flipper. Where do I go or is there a website that thus part can be ppurchased.

I would look for good used. Ebay or Pull-a-part junk yards.

Thanks for your help and guidance and happy holidays.

Yes, thanks and same back to you.