Just replaced the engine due to being run low on oil. Although the previous engine was starting to knock, it accelerated and ran ok to the shop. After installing a used engine in the car, the car has a very long crank time before firing (but turns over well) and then has a very low idle (500-750 RPM) and throttle response is poor at best. Acceleration is so lacking that the vehicle can not be driven. In park I can get it to rev up (no odd noises). If I hold it at part throttle for about 2-3 seconds and then it will catch up but feels bogged down. I have changed out the electronic throttle body, spark plugs twice with two different gaps, fuel rail and all injectors, crank sensor, cam sensor, (all parts came on the used engine, and I have swapped them out for the ones original to the car with no change. Only part that is on it now that is not original to the car is the intake manifold itself) and checked all harness connections including MAF. There is no Service Engine Light on.
My car has 125000 miles.
My car has an automatic transmission.
Hi there, thanks for writing in. I’d be happy to offer my insight. I would suggest checking the idle air control module. If the motor is starving for air (similar to an engine being choked at normal operating temp), this may cause it to bog down as you describe including the very low idle. As you may already know, if it were a leaner fuel condition such as a vacuum leak, the tendency is for the idle to naturally be higher.
If you would like help, consider having an expert automotive technician from YourMechanic come to your home or office to inspect and diagnose this issue for you, and make any repairs as needed.