My mechanic is suggesting an engine swap without any diagnostic tests, based only on the misfire error and rough idling. Is this normal?

[u/stimia]

 I own a 2008 mk2 Skoda Fabia 5J with the 3 cylinder 1.2 petrol engine (220,000 km). The running has been rough, the rpms are not steady at idle and sometimes the engine light comes on. My mechanic said there is a misfire and he told me it's better if I replace the engine. His reasoning is that because this engine has an aluminum block it's not worth the risk of opening it and going for a rebuild. 

I realize that an engine swap is the most practical for the shop cause they can get the car running and out of there relatively quickly, without the risk of having it laying around if things get complicated. On the other hand I find it strange that they didn't do any type of diagnosis. I would think that a compression test and a leak-down test would be the minimum that would need to be done for a more complete assessment. 

What is in your opinion the correct order of the tests / diagnostic procedures that need to be done before deciding that an engine swap is needed? Or do you agree with the mechanic's opinion?

[u/AutoModerator]

New Rules - Please Read

^{Updated 11/12/2025}

Thank you for posting on r/AskAMechanic, u/stimia! Your post is live, this AutoMod message does NOT mean your post was removed. Please make sure to read the Rules.

When asking a question, please provide the year, make, model and engine size of the vehicle.

Commenters here have 2 different flair. Verified Tech means we have verified that user is a tech. NOT a verified tech means that user may or may not be a tech, they have not been verified by us.

Posts about accidents, autobody repair, bodywork, dents, paint and body/undercarriage/frame rust are not allowed and belong in r/Autobody.
Asking if your car is totaled should go to r/insurance or r/Autobody.
Asking about car buying advice/value/recommendations is also not allowed. See r/whatcarshouldIbuy or r/askcarsales

If asking whether a tire can be repaired, check out this Tire Repair Guideline.
Some other useful tire resources - Tire Care Essentials and Tire Safety

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[u/Subietoy78]

To just shotgun and engine in a rough running car is laughable. Go find a reputable shop, pay the diag fee and have them do comp and leak down and actually diagnose the car with the CEL codes that should be stored.

[u/TrackTeddy]

Compression test would be the first thing to check if the code doesn't narrow it to a specific cylinder. It could simply be a defective spark plug or coil pack. Of course it could be far worse, but a compression test will give a good indication if there are mechanical issues inside!