I have a 90 FC and it has a strange idle. When stopped and no pedals depressed, the idle will fluctuate slightly from 400-700 rpm. I did a little research and I heard this was a common problem for the '90 model only and it requires placing an orifice in the Idle Air Bypass Valve. Anybody have any idea what this means or has anyone done it themselves? Any help would be greatly appreciated. Thanks.

 

uh, yeah right a orifice on the idle air bypass value... who is feeding you that crap?

The 89 though 91 used the same everything as far as the motor is concerned... so saying it was a '90 only problem would be wrong.

It sounds like you have a TPS that is out of adjustment. Not some made up missing orifice.

 

Read the 2nd Gen FAQ....good info on everything about the FC. As Icemark said, try adjusting the TPS first. Then if that doesnt work, add a orifice...lol

 

When I got my 87 back it would do that jumping mess. It didn't seem to hurt anything but wasn't cool.

Besides adjusting the TPS (which didn't help my case). But first I adjusted the TPS blindly and it solved the fluctuation, but that caused the TPS to probably be way out of adjustment which caused the engine to stall at WOT above 5k rpm.

So, spend the three bucks on a TPS tester.

And something else I haven't figured out was the 10mm adjusting nut on the throttle body. My neighbor did this and was much better afterwards. He told me not to ever mess with it, so I assume you can do some harm if you do it wrong.

 

Thanks for the input people. The orifice idea came from carreview.com I believe. I found it a little strange too that they said it was a '90 only issue because all S5 engines should be the same.