S5 Swapped GSL-SE High Idle. Need help troubleshooting
06-12-20, 08:52 PM
#1
S5 Swapped GSL-SE High Idle. Need help troubleshooting
I swapped an NA S5 13b into my GSL-SE and am having trouble with a high idle. The car is still running off the GSL-SE ECM, injectors, and vacuum solenoids etc. so it's basically a GSL-SE with an S5 keg and S5 intake+TB. I figure GSL-SE idle troubleshooting is the most relevant.
It idles around 1200rpm. If I twist the throttle shaft all the way closed by hand I can get it to drop another 100-200rpm or so but that requires some pressure. The throttle plates are already more closed than on my old GSL-SE throttle body at idle. Other symptoms of trouble are small spikes in RPM when I let off the gas to shift, and occasional surging when I push the clutch in and put it in gear at a stop (it'll drop from 1200 to 600 then bounce up and down). It also bucks under very light throttle when I'm driving, although this could be due to using a GSL-SE TPS on an S5 throttle body with a longer arm hitting the TPS plunger.
What I tried:
- Set the TPS for idle with the throttle plates all the way closed using the standard GSL-SE procedure
- Set the timing at my 1000rpm idle with vacuum advances disconnected and plugged
- Put 20psi of air in the intake at the AFM. No leaks found except a slight one under the thermowax where the slit is cut in the gasket.
- Adjusted the throttle body so the throttle is not hitting any throttle stops when closed
- Adjusted the fast idle cam so it's working correctly (disabling it doesn't drop the idle either)
- Plugged the BACV to see if idle dropped (little change)
I know there are 'typical' GSL-SE issues that can cause idle problems, but in this case it could be something different and less common because of all the stuff I did to get this working on an S5 block. Any information on what else could be affecting idle is appreciated. Everything is new and freshly built, including the throttle body.
It idles around 1200rpm. If I twist the throttle shaft all the way closed by hand I can get it to drop another 100-200rpm or so but that requires some pressure. The throttle plates are already more closed than on my old GSL-SE throttle body at idle. Other symptoms of trouble are small spikes in RPM when I let off the gas to shift, and occasional surging when I push the clutch in and put it in gear at a stop (it'll drop from 1200 to 600 then bounce up and down). It also bucks under very light throttle when I'm driving, although this could be due to using a GSL-SE TPS on an S5 throttle body with a longer arm hitting the TPS plunger.
What I tried:
- Set the TPS for idle with the throttle plates all the way closed using the standard GSL-SE procedure
- Set the timing at my 1000rpm idle with vacuum advances disconnected and plugged
- Put 20psi of air in the intake at the AFM. No leaks found except a slight one under the thermowax where the slit is cut in the gasket.
- Adjusted the throttle body so the throttle is not hitting any throttle stops when closed
- Adjusted the fast idle cam so it's working correctly (disabling it doesn't drop the idle either)
- Plugged the BACV to see if idle dropped (little change)
I know there are 'typical' GSL-SE issues that can cause idle problems, but in this case it could be something different and less common because of all the stuff I did to get this working on an S5 block. Any information on what else could be affecting idle is appreciated. Everything is new and freshly built, including the throttle body.
06-22-20, 09:55 AM
#2
I know this is a weird issue due to my swap, but can anyone help me figure out why the RPM drops and surges when I put the car in gear with the clutch in? In a typical GSL-SE I'd assume my throttle plates aren't closing all the way and I get a feedback loop, but I can confirm my throttle plates are closing fully (S5 throttlebody). Is there a neutral switch or something that will impact idle?
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