Rough idle

[steve]

Hello Forum,
Recently timing belt was replaced on a mazda protege 1999, 1.6L, manual transmission. Rite after the belt replacement, rough idle set in. Car starts fine without any issue. As the idle begins to go below 1K rpm, thats when the rough idle sets in. Vibration is felt inside the car, on the driver seat. The needle at RPM meter clearly shaking, its not steady. On the tail pipe, steady stream of exhaust sound changes, its like exhaust coughing, absence of steady exhaust streams. In the air filter compartment area, there is a sound of knock around the same time.
All the timing marks were accurately set. Cam and crankshaft timing marks are correct. Compression test results came out ok, All cylinders were around 180 psi. Car is not overheating. Temp gauge is in the middle. Air intake system checked out ok. Fuel, ignition systems are good.
What could be the issue for rough idle? Before the timing belt replacement, there was no rough idle.

Topic

[Its me]

First check all wiring/cops, plugs electric connections and ensure that everything is hooked up correctly.

If you cannot find anything wrong here, or anything disconnected, the you have to go back and check the timing belt locations again…. If it worked proper before… it is something you did….

All the best…

-Karl

[Brian]

The timing marks can be lined up, but #1 cylinder may be opposite of top dead center. Timing is definitely off. Good news is you were just in there so you know your way around it.

[steve]

Good point. The Piston top is at TDC. By inserting a screw driver on each cylinder and noticing how far high it can go with the timing marks aligned, gave the sense of TDC. So the TDC on all cylinders seems to be ok. Car starts fine on the first take. No hesitation.

[Author]

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