I am in the middle of swapping an engine from a wrecked FC into a spare shell. I have everything swapped over and it fires right up. I can not however, get the idle to set correctly. Here is what is happening (video):



When I unplug the TPS, the problem goes away. When I adjust this screw, the idle will smooth out but will not go below 1000 RPM:



All of this being done without the throttle cable being connected. When I pull backward on the linkage holding the above screw, the idle will drop below 1000 RPM. So it appears I have a couple issues. The only info I could find in the FSM about adjusting the TB involved using a test connector/LED's which I do not have. I am also getting a check engine light if that has anything to do with it? Here are a couple pictures of the TB. Thanks

 

i would check the codes, if you ran it without the TPS hooked up, it'll have those two at least.

the S5's have a closed loop idle control, so if the speed is out of range it'll hunt like that.

step one is to make sure the throttle is actually closed

step two (you should have seen this coming!) adjust the TPS

 

and adjust the idle air screw, top middle of the throttle body with the black rubber cap on it.

your thermowax might be getting old and sticky which is holding the idle partially open, this has been a pretty common problem lately.

 

Thanks, I'll give those a try. Is there a way to adjust the TPS without the LED tester thing? I figured there would be a way to adjust it with a DMM.

 

backprobe the green wire, fully warmed up, key on engine off adjust it to read 1 volt.

 

By adjust you mean twist the screw that is shown on the first picture? The one with the screwdriver in it?

 

yep

 

Thanks. I'll give it a shot when I get off work tomorrow.

 

we used to sell a lot of those at the dealership. we actually used to stock it. i've never personally had a bad one, until recently, 2 cars in a row

 

yeah, i haven't seen a single issue with them until the last couple of years also. must be their lifespan alarm has been triggered. in some cases though it was just simply the coolant passage was plugged up so there was no coolant flow through the thermowax, so it always thought the engine was cold.

 

when mine had an idle like yours it was a vacuum leak. worth checking

 

i got it to stabilize at 1000rpm which is good enough for now. now i need to find out why the brake lights wont turn off