pretty much since ive had my car, for about 25k miles when it reaches a high temperature it seems to run pretty bad at times, but it is usually fine if i have the heat on (atleast low defrost) i was able to deal with it.. but then a few days ago my car started to do something i dont like... i think it is only when it is warmed up but now it has a severely bad hesitation and you can hear a knocking type sound... and if i go up a hill it does it too.. cant tell exactly where it is coming from, but sounds like its around the engine... and occassionaly if i put it into 1st or 2nd gear it seems to not hesitate as bad going up hills ( may just be coincidence) any ideas of what i should look at?

the service engine light is not on..

thanks...


its a 94 z28 a4 122k miles

 

When was the last time the car was tuned up (plugs, wires, air filter, fuel filter, O2 sensors)? When was the coolant changed last? Are you using 91+ octane fuel?

 

wires changed at around 99k
plugs, o2 sensors and cat prolly around 110k
fuel filter was about 100k...
coolant i really need to do.. it hasnt been changed since i got the car, it needs flushed .. premium... made the mistake of using 89 octane one of the first times i got gas, and she was pissed, you could tell she didnt like it (which is what led to the fuel filter being replaced..)

when it first happened, i was driving out to my moms house and before i got onto the highway it started making the sound and the sputtering... once i hit about 40, it was fine.. cruising the 40 minute drive at 70mph no problems, until we got off highway around 35 mph zones... on the expressway it was fine to even go full throttle no sounds, no hesitation so it seems to be 0-40 speeds ?

 

Hook up a fuel pressure gauge to the test port on the fuel rail. Temporarily tape it to the windshield and monitor your fuel pressure while driving. You should see approximately 35 psi in part throttle driving and 41 - 46 psi at WOT.

 

ill have to see if anyone has one i can use... or are they not expensive , or auto stores rent them out? if i find one ill let ya know how it does...

 

They're not that expensive and it's a valuable trouble shooting tool for any car.