87 S4. Intake refresh including all sensors done and rebuilt MAF. Injectors and dampeners and regulator all done.
It's done this before and after all the work, when at full operating temperature, when I go to restart if the car has been off for a bit, I get very low, hunting idle. After about 5 seconds it clears up and idles fine. Runs great, no other issues. Any ideas? I replaced the ISV too.

 

Have you checked w/ a meter that all the sensor signals are making it back to the ECU's?
Also just because a sensor is new does not mean its good

If was my car the first thing I would do is connect it to a Shark Tuner and see what the ECU's see.

 

Good idea, I need to hunt one of those down. Maybe someone close to me has one that I can borrow.

 

How are the fuel regulator and dampers?

If leaking, it will give you problems (hard start, rough idle for few seconds).

Just saying.

 

^^^^ my money is on dampers/regulators. my car had the exact same issue

 

I would agree on that too (as it sounds like it's rich) but the OP stated.....
"87 S4. Intake refresh including all sensors done and rebuilt MAF. Injectors and dampeners and regulator all done. "

So that lead me to a signal issue

 

Good point Dave.

I missed that.

Sorry.

One other (small) thing, how is the fuel pump check valve?

 

I will check the one at the front- looking back at my records I did not change it. Both the rears were done. Bertrand, where is the fuel check valve and how do you test it?

Thanks

 

The fuel pump check valve is between the fuel pump and the filter.
Don't know how to check it though.



Edit: Might worth just changing it as it's not that expensive. About 20$ IIRC.

 

Thought issues with this pressure retention valve were involved with rough starting, and not idle issues.

 

You're right Craig.

Don mentioned that after about 5 seconds it clears up and idles fine.

"...I get very low, hunting idle. After about 5 seconds it clears up and idles fine...

 

I checked the dampeners and regulator, all hold vacuum. I was looking around for info on the fuel check valve (Thanks Bertrand) and found out how to test it, in case anyone needs to know:
http://www.nichols.nu/tip561.htm

Still want to hook up a sharktuner but need to find someone who will loan one out.

 

The symptoms do match those caused by leaky injectors.

You say the injectors are "done", but were they leak tested ?

Have you monitored fuel pressure after switch off, to see how quickly the pressure drops ?

 

[QUOTE=John Speake;12919853]The symptoms do match those caused by leaky injectors.

You say the injectors are "done", but were they leak tested ?

Have you monitored fuel pressure after switch off, to see how quickly the pressure drops ?[/QUOTE
No I have not. The injectors were sent out to Witch Hunter for rebuilding. I don't believe they were leak tested. As far as I recall they clean them, flow test and new seals. I need to look into this, as yesterday after thinking about it and considering all the work I came to the same conclusion as you but I dont have much experience with injectors and this mode of failure.

Thanks for the tip John.

 

My understanding from what Witch hunter would know while doing their testing is that they should see and find a leaking injector.
However old parts do and will eventually fail, it is possible that what had passed their testing is now leaking.
You can test them yourself, but they all need to be removed, watching for a fuel pressure drop would be first on my todo list before removing them