Hello all!
helping a friend replace the timing belt on a ‘12 Cruze 1.8L. The car ran fine previous to this.


We installed a new water pump, timing belt tensioner and pulley, and of course new belt.

the car idles rough and smooths out with gas. It has two engine codes one for camshaft B and camshaft A. We installed the timing belt with the factory pink camshaft marks across from each other exactly and the crankshaft mark on exactly.

Once installed we turned the crankshaft by hand two revolutions and the camshaft marks were still right across from each other.

I’m at a loss what we did wrong, any insights?

we have checked for unplugged sensors and the air filter appears snug.

 

Check the MAF sensor and the wiring to it. Also check to make sure that the hoses to the air filter box were all installed and have no leaks.

 

Sometimes a vacuum leak allows extra air to get into the engine , the ECM responds and enriches the injector on time resulting in a rich condition where when you open the throttle to allow more air in it smooths out.
As stated in an earlier post look for unmeasured air getting in without going past the MAF sensor.