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rough idle, ECU adaptation and vacuum lines...

1K views 2 replies 3 participants last post by  sleepy3863 
#1 ·
Hi,

This is my first posting...I recently came into a 92 9000 CD Turbo with 93k and a rebuilt engine. Long story, but I loved the car and the price was right (<$3k with new tires. Bought it from the shop where my VW is serviced....they do SAAB's as well).

Anyway, the idle had been gradually getting slower and rougher over the past week. This morning it was cold, so I went out and started it up and let it run for 10 minutes before sending my wife of in it. When we came out, the RPM's were below the dash below 1000 and it stalled the minute you put it in gear.

A lot of internet searching later, I checked a few things out. The engine rebuild had resulted in most of the vacuum lines being replaced except for the ones connecting the "hooter" valve (which is, well, hooting nicely for me) and the control valve. These older lines had flared ends and I cut them off and pushed them onto the control valve. I did check the charge bypass valve (hooter) and it does hold a vacuum.

So I started it up and it still wanted to idle way too low. So I disconnected the ECU, reconnected and after that, it idles beautifully bang on at 900RPM. Turbo works great, and the MPG displayed is MUCH better for the 5 mile test drive I took.

So it appears that the car "learned" to idle poorly and it accelerated that learning this morning. Once I unlearned it (sorry), it drove great. I know there are a lot of reasons for the rough idle, but would the fact that it learned how to do it slowly over time indicate one thing over the other? Is this typical behavior?

Mostly I am looking for anyone that might give my guidance if this is NOT a typical vacuum/valve issue.

Thanks in advance!
 
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#3 ·
bringing an old post back from the dead, i am curious about this one... being a 92, it would not have a trionic ECU, so would it actually do any good to unplug it and plug it back in? i thought that the LH ECUs didnt learn as the trionic ones do? anyone able to shed some light on this?
 
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