the engine is a s5 n/a

the car idled like a champ before hand.

I started up the car this morning and it idled like crap. Ive seen the bouncing idle before but this one bounces at about 2x the speed they normally do.

The car drives fine over 2k rpm almost feels faster, but I think my mind is messing with me.

it doesnt have a hard time starting like i would expect with a bad vac leak or chipped apex seal. and under wot it sounds normal too.

any thoughts guys?

 

Typically a vac leak, TPS problem, or both.

 

tps sounding to me

 

I have the exact same problem with my S5 turbo. I have messed with the tps a bunch. I also set it a few times with the TPS adjusting lights, But it still does the bouncy/surging between 1400-2000 RPM's....

I want to get the engine "smoke tested" for vacuum leaks....

 

i had the axact same prob, turns out my main rail wasnt sealed and leaking

 

TPS sensors have resistance issues.

The only fix is a new TPS.

Or you could just deal with it.

 

thats all good and well but the engine cannot idle above the amount of air it recieves. Correct me if im wrong but the tps only effects fuel delivery if im correct. I listened for vac leaks with a length of hose but I heard nothing. Im thinking it still a vac leak though.

 

When you start the car in neutral, does it start with an accelerated idle at 3000 rpm, drop to an elevated idle of about 2000 after 15-17 seconds, start bouncing between 1400 and 2000, then finally settle at 750?

 

no it has most emissions and idle acessories removed all thats left is the iacv and my safc to adjust it out.
the safc still shows a decent tps reading and i have no engine codes.
car is an 88 so im using the 2 led method.
it worked fine yesterday and i changed nothing. i just cranked it up and it started doing this immediatly

 

It was actually a failed IACV. swapped it out and everything is golden again. Thanks for your time guys