I have an S5 with a55k on it, I wouldnt idel at all after i started it, i replaced plugs, wires, exhaust, intake, and fuel filter, nothing helped any excpet fuel filter. It now idles a lot better, but after driving on highway and pulling off ramp the idel drops to about 175 to 200 rpm and kinda bounces around, any ideas on what it could be?

 

TPS? Primary or Trailing Coil or both,but sounds more like a dying fuel pump, dirty gas, vacuum leak, old battery, and idle bouncing could be alot fo things, check all of these and look for more suggestions, but remember, when it comes to repairs do all the CHEAPER ones first and work your way up. chances are the cheap crap needed to get changed anyways. good luck man

 

Well, i have done most of the vaccums, replaced the filter, and put in an optima battery. It helped a little after the fuel filter. I am thinking maybe fuel punp or ignition or coils, i want to add a jacobs ignition re amemiya wires, and some high performance coils(any recomendations) and a walbrough pump, do u think this will fix it??? also, I was told it could be because of my exhaust, it has duals, a catco cat, and the pre cats were removed in favor or a straight pipe, could back pressure be the problem? Injectors? Anything, thanks again

 

*Bump* because I'm having the same problems with my '91 coupe. I just put in an APEXi intake & RB true duals(no cats, just presilencers)), and about 2 weeks or 500 miles later, the car won't idle at all. Anything under about 4k rpms and the car really sounds rough.

Any help is much appreciated!

 

Have either of you guys pulled the fuel pump out to check the "sock" (low pressure) Filter on the pump itself? If you know you don't have a vacuum leak, and your battery is good, I'd check your grounds and pull your fuel pump out (might as well just replace teh fuel pump filter, as you know it hasn't been changed yet and it costs 5-10 bucks). It only takes about 5 minutes to do, if your screws aren't rusted