Car is S4 NA Started the car up and was shaking horribly on starting sometimes it does it sometimes it doesn't so I have it some gas kinda pushed past it settled down after a couple secs like usual idled fine drove it down the road fine started acting wonky about halfway down the street going around 60 kinda hesitated a bit and dropped down so I let off the gas kinda still felt that feeling went to the light to turn around and I hear this loud *** slap behind my car and I was like oh **** min you my car has never backfired or anything did a uturn limped it home checked engine looked visibly and sounded visibly sound checked oil looked good no fumes or smoke coming out of the exhaust no smoke from engine not visible leaks no fluids

 

I think the first step is to perform a proper compression test on the engine with a rotary compression tester. See where you sit before throwing any money into anything else. If the numbers are good, we can go into diagnostics.

 

Your right and I did a compression test about a month a go when I changed the plugs blew 85 psi on all 3 facings for leading and 95 on all 3 for trailing which 85 is spec according to Haynes manual

 

sounds like a bad misfire, though strange how it'll fix itself. Got anymore details? Just started today? do any kind maintenance prior to this starting?
also as far as your compression results, I have the manual your talking about, the number they have in the manual is the minimum compression not spec but considering how all faces are above minimum and equal that's at least the good thing.

 

Yeah it is weird it has done it half the time on startups where itll shake then I push through it with the gas and its fine.. Sometimes it takes one turn to stsrt sometimes it takes 6 loll but it always cranks and comes right on and maitentince since ive had the car, koyo rad took upper intake manifold off and re did all the vac hoses fuel lines coolant lines, my bac valve is non existent my soeloid for it broke so I plugged it, fuel filter, new spark plugs, deleted to omp and blocked it off and that's about it. And gotcha gotcha I was assuming it's minimum car has 162k miles so it's to be expected

 

So there are a couple of things you could do from here. Check your plugs and ignition system (coils/plug cables), I would also recommend giving your car a smoke test to check for a vacuum leak. my old s4 NA shook so badly it broke a motor mount and it was because of a leak from the emissions system, it only shook on idle but its worth at least looking at in your case. I'd be interested in seeing what you find