I notice an occasional, noncontiuous tap in the top of my engine, possibly under the intake manifold?

Question

This is a 2002 Ford Explorer XLS, 4.0L SOHC 75k miles. I had my routine oil change and a few days later I notice "the sound" which is one single tap which returns every minute or so. Usually it is more noticeable after a cold start. I have a Service Engine Soon light on the dash and the computer code reads, "insufficient airflow" or whatever....due to a bad EGR or EGR sensor. The performance/MPG, etc. does not seem to be effected at this point. This sound is also comparable to the pops and clicks you hear when your engine is cooling, but just ONE tap and every so often. I ran synthetic oil in the truck for it's first time a few months ago, taking the advise of the lube tech. I now am running Motorcraft synthetic blend. I have heard a lot of different things that this sound could be, just need to know if anyone out there has had a similar problem with their Explorer.

-Oil level is good

-Ran fuel injector cleaner

-Dumbfounded

Thanks.

Answer 1

check your vacuum lines and purge solenoid use the engine sticker on the hood as a guide, make sure your oil filler cap is on

mechanics often inspect the vehicle to up sale you they could have knocked something loose while taking the air cleaner loose