My Cadillac STS jerks between 1,500 and 2,500 RPMs. Mechanic says it is not the transmission. What is it?

the EGR valve.~

Idle fast?

That would cause the car to jerk?

Idles just below 1500 rpms. The mechanic is also replacing the timing chain. I thought it was the tranny at first but they ran tests on it saying it was fine so they replaced all the coils and spark plugs and took it for a test drive and told me it was fine but heard a clink sound so they think its the timing chain. You the EGR valve would cause this?

looking for an example (that don't ask for money)~

https://www.youtube.com/watch?v=Roz6jVN7S-k

Can you copy and paste the egr valve cleaning link again?

the timing chain will continue to stretch until the wear shoe has run out of real estate, the stretched chain can be fixed....a broken one will destroy nearby components (like the oil pump, for example)~ if it sounds like a coffee can full of marbles would change the timing chain immediately~

at first I thought what's the big dealie-o, opens up on decel, closes on acceleration...but it is more complicated than that...has to introduce exhaust gas if the combustion temperatures get too hot...as measured by the MAF sensor and 02 sensors~...yeeeef~

I do not have a answer, but my Cadillac sts 2006 is doing about the same. I just changed all the coil packs and spark plugs for it. When I get about 2000 RPM is wants to ride rough but if I give it some power it will go with no question. Check engine light will also flash.