ColinB

For years I have believed that my car has always had a slightly high idle speed. It sounds high and the tach shows about 850-900 RPM. But I recently ran it on a Bosch diagnostic machine which measured it at 775. This is exactly right for the GT engine.

However, it doesn't sound right to my ear and I'd like to experiment with a lower idle purely for aesthetic reasons. I know the GT is designed to idle just a little faster than the S4 because the cams are a bit harsher but I think my car would probably tolerate a 100-200 RPM reduction.

Trouble is, there's no idle adjustment. It's all in the electrickery (and I'm electronically challenged, wouldn't know a microfarad if I tripped over one). Does anybody know a way to do this?

Colin. 89GT.

daveo90s4

I understand that John Speake's SharkTuner has a function for adjusting idle speed (and max. revs and just about everything else too). Possibly he'll respond?

AO

DaveO is correct. The idle is controlled by a setting in the LH Chipset. This can be reprogramed by the SharkTuner, but that's about all there is. FWIW, mt tach shows my idle at about 850-900 RPM, but when I hook up my diagnostic computer and my dataloger, they both show idle at about 750 which is correct for my GT.

ColinB

Thanks for the advice guys.
I have John's "spanner" (Same as the Sharktuner I think). I've watched it go through the idle reset programme but it doesn't reduce the RPMs because they are already correct as per the Bosch diagnostic tester. What I probably need is a custom programme for the spanner. John?

Colin. 89GT

John Speake

The Spanner is just a diagnostic tester (which can also reset the idle speed, as you observe).

The SharkTuner is a completely different animal designed for remapping the LH and EZK ECUs. See my website.

The easiest way to reduce your idle speed would be to fit an S4 EPROM in your GT's LH ECU.

ColinB

The master speaks.

Thank you John. I know where to find an S4 ECU so I'll try that. Is the rest of the GT programming the same as the S4 then? How about redline, the GT's is slightly higher.

Colin. 89GT

John Speake

The fuel maps are virtually identical, S4/GT/GTS. Yes, red line is a little higher on the GT IIRC. I can always supply you a custom chip with S4 idle and GT rev limit. (or higher if you want)