Hi everyone, sorry for another idle surge thread, but I couldn't find anything happening exactly like my issue. I just picked up my 89 GTUs this past weekend and am still very new to the rotary (loooong time lurker).

So basically here is what's going on:

S5 N/A. Bone stock other than the PO replacing all vacuum lines with silicone hoses.

Starting cold, the car will do cold start procedure. Sometimes 3k, sometimes 2800rpm, sometimes 3500 rpm.

After the cold start procedure the car will continue to idle steadily at 1800-2000 rpm depending on the day.

After 3-4 minutes of idling, the idle will start to surge between 1200-1500rpm. It seemed to go away if I turned on the headlights. Kinda weird.

Once the car gets warm after driving around a bunch, the idle is rock solid around 800rpm.

Taking the car to redline, the car feels like it loses a bit of steam past 6500rpm, and i get a hesitation at 7500rpm.



I adjusted the TPS to 1000ohm (it was reading 945ohm initially) as aaroncake mentioned in the TPS adjustment 101 thread.

Cold start seemed to be a dead even on 3000rpm and it seemed a bit smoother, but my idle surge is still there....just delayed a bit further, till around 5 minutes. High RPM hesitation is still there.


I was going to replace spark plugs, wires, and clean the grounds this weekend when I have time, but is there anything else I should be looking at while I'm in there?

 

double check the Vacuum hoses again. that 7500 hesitation should be from it.

 

it's actually rather normal for an S5 to do this for a few minutes in interim from cold to warm.

you could try turning down the idle, but then you may have stalling issues as the BAC isn't exactly the most responsive on these cars. unfortunately it's an old car and sometimes you just have to live with small little things like this surge, or spend hours dialing in the throttle body, thermowax and BAC settings and that isn't something i suggest for someone without a lot of experience.


high RPM hesitation is unrelated, most likely due to out of calibration fuel system, sticking secondary ports/VDI, clogged cat, worn spark plugs/wires, etc, etc, etc.