Alright, here's my problem. (why is it i've never seen a s5 idle properly?)

1989 GTUs

My car has NEVER idled properly since I bought it, it's always idled high/pulsed. TPS checks out just fine, so I adjust it, doesn't help, still idles high (no more bounce though, just idles damned high). I know what you're thinking, vac leak! Yeah, 5 bottles of carb cleaner later, I've determined there are NO leaks. So, I decide what the hell, might as well rip off every damn vac line on the vehicle and go bare block, and I've still got the same damn problem, which is.

Car when it wants, will idle at 700, 1000, 500, 200 rpm, whichever it feels in the mood for. I've grounded the initial set, got the car to sit at ~750rpm, verified the TPS checker only had 1 light on, turn car off, remove wire, start it up, low and behold 750rpm (or so). I rev it up once, and now idles at 1500, with a searching idle. TPS still reads the exact same ohms, still only 1 light on (when i go out and recheck it). No matter what I do, once I get it rock solid at 750, then rev it up again, it'll never come back to 750. Any ideas before I thermite this god damned thing?

 

Well, if you still have the ACV, you could have busted diaphragms that could produce a vacuum leak that no amount of carb cleaner will find. Same idea with the EGR valve.

Look for recent thread by user wozzoom about idle woes.

Hugues -

 

Well, one part I didn't see in the thread is the BAC. Had a similar problem on my S5 TII. Idle @ 1000 rough, idle 800 ok, up and down at various times. BAC was operating properly via electrical checks, but the internal seal was leaking. Removed BAC and blew through the air supply tube-Seal didn't hold. Cleaned with carb cleaner and only lasted a couple of weeks. Replaced BAC and no problems since. That was last year.
Make certain that TPS is set correctly. If you use ohms or volts, double check the setting with the Mazda Check Connector....Very important.

 

Also check the TPS Ohms value to see that it repeats & that the sweep is smooth.

Also the spring inside the BAC can be tensioned a little more with the hex drive set screw in the solenoid end.
That will sometimes help a worn internal plunger to seat better.

 

Already checked the TPS with ohms, volts, and just about everything else. It always sits in the same position (.99kohms, 1.02volts or something like that). The BAC wasn't helping, so it was removed to see if it was the culprit, it hasn't been yet. On every once in a slight occasion, it'll idle itself down to normal, and will idle fine, a few seconds later and it's back to being a pain in the ***.

 

I assume your stating the BAC has been removed, and the TPS, although the values stated look good, has been checked with the checker?
So we've eliminated vacuum leaks,tps,bac...Wonder what's left? Throttle plates returning all the way? Just a thought.

 

try a new ecu

 

Correct, BAC was removed to determine if it'd help any, it hasn't. TPS checks out just fine with the checker lights (when it idles at ~750rpm) Then, I rev it once, and it stays at 1500 and bounces (even tho the check light is fine, and the TPS values are fine). The throttle plates are bugging the **** out of me, mainly because I have no idea how they're supposed to sit at idle, and sadly the FSM has no information on this either.

 

throttle plates could be a problem if your gas pedal cable is sticking
or cruise control cable if u have it is sticking to something
adjusting screws could be out

 

Cruise has been removed. Definatly not the throttle cable, i've checked that over and over. At idle is there supposed to be *any* opening on the throttle plates (once the AWS, if you still have it, has let it drop down to 750?)

 

I'm in work, but I thought the FSM mentioned the setting of the plates. Could be wrong, will check tonight.

 

it only mentions how much gap there should be before the plates start moving together, but it doesn't say how much gap their should be while they're both closed.