I'm having some unusual idle problems with my 91 N/A S5. When I start my car, my idle is good at 2000, then when my temperature gets warm, my idle drops to 1100-1800 depending on the day. It doesn't drop from there until i drive it. Once I start driving, my idle starts to stutter and jump between 100-1000 rpms and occasionally die out. I have replaced my TPS and MAP sensor since I had the check engine lights and that what the codes asked for. My idle was the same before I replaced these parts. I had read on another thread to disconnect the BAC and see if it dies out. I did do that and it did die, but I really don't know what that proves. Sorry for the long vid, but I tried to offer as much info as possible. If you have any ideas or advice, I would greatly appreciate it! Thanks!

http://www.youtube.com/watch?v=HLUFg62DEYM

 

Vacuum leak? haha IDK. maybe the Air pump. It sounded like my old 87 N/A RX7 I got rid of a while back but it never died out like that or dropped below 600 rpms

 

you replaced the tps; but have you adjusted it or ohmed it out to make sure it's within specs? The fsm has 2 easy ways to adjust your tps........

also look in the fsm for fast idle cam adjusting....

try these......

also check for vaccum leaks after the engine has warmed up. spray some carb cleaner around the intake and see if the idle changes. If it does then concentrate on that area for possible leaks...

 

The 2000 rpm while cold sounds like normal operation of the AWS, though it supposedly should be 2500-3000. It should drop to 1500 rpm after 17 seconds, and then ramp down to 750 as it warms up.

It may be that you are not cold enough to trigger the AWS at all, and the 2000 rpm idle is from an out of adjustment fast idle cam. Something is going on with the cam, because the idle changes after you drive it. That suggests that the roller is not coming off the cam until you open the throttle.

The poor/variable idle after you start driving sounds like a vacuum leak, or a non-operating BAC valve, or both.

 

I did the adjustment for my TPS (I hadn't done it prior; obvious newbie mistake), but I used a voltmeter and the the 3 slot plug on the right side by the strut. I was able to get one side of the plug close to 11.7 volts and the other side at 0 volts. I'm not sure if this is close enough. After I did this, my idle is at a stable 750 rpms but now I'm really struggling to start the car after its been running for a while. It seems as if its flooding because after I get it started, it wreaks of gasoline and white smoke comes out the pipes. But once its running its awesome. It looks like I'm going to have to do some more research tonight. Thanks for the advice and I'm still going to try the carb cleaner thing since i get an occasional hiccup in the idle.

 

Check compression