968/92

Spent the last month trying everything to resolve my high idle/stalling when warm on my S4. I have read ALL threads that could be related with this issue here and on other forums.
Here are the symptoms:

-The colder it is the better it will run in the morning. It will idle at 800 rpm and run smoothly, no gas smell, if I put my hand near the tail pipe the exhaust air is coming out smoothly if that makes any sense.
-When it starts to warm up (5-7 min period) I can gradually start to smell gas and the exhaust coming out is not as smooth.
-At some point 5-10 min later, it tries to idle at the usual 675 rpm for 5-10 seconds but it will run very rough. If I give it gas, it will stall sometimes when I let go. However if I wait, 10 sec, the idle will climb back to 800 and makes its way to 1000 rpm as it reach operating temp.
-If I shut off the engine and turn it back on, it will try again to settle at 675 rpm for a bit but runs rough and climb back up to 1000 rpm with gas smell.
-The interesting thing is, at any point during start up-warm up-operating temp, disconnecting the Temp II has no affect whatsoever. I tested the Temp II in boiling water and at the and EZK both while cold and warm. Both terminals showed same value at the sensor and LH/EZK and were within range.

I expected the engine to cut out right away when I pulled the Temp II (infinite resistance, dumping fuel). That was before I tested the resistance at the LH/EZK so I expected bad wiring to them so they are using some pre-determined setting to when the Temp II fails but that was not the case, same exact resistance at the sensor and LH/EZK connextor. I have read a bit about the LH failures but was not able to find someone with similar symptoms.

Two questions:

1-Can somebody just unplug the Temp II on an S4 and report what happens?
2-Do you think my my LH is toast?

soontobered84

I asked this in the other forum and never got an answer: Are you sure that you are unplugging the Temp II sensor and the temperature gauge sensor?

Some pictures might help us know what you are dealing with.

968/92

Yes Temp II for sure

PorKen

Have you tried unplugging the O2 sensor? Is the correct coding plug installed?

The S4- LH will default to a warm value if the the Temp2 is not within a plausible range.

Checking for codes with a Hammer/Spanner/Theo might help you narrow down the cause(s).

968/92

I guess you're missing a "not"? Or should I unplug both of those sensors at the same time?

968/92

O2 was unplugged for some reason when I got it. It's plugged now and seemed to have dropped the idle just a bit (was around 1100 rpm when unplugged). I tried unplugging it while engine is running and the engine stalled so I guess it is doing something.
Temp II is within range and the problem is non existent when cold.

soontobered84

I guess I was subconsciously trying to minimize the negativity in my life and left out the "not". Unplugging just the Temp II should make change.

Taguid

I have the same problem and have tried all that you have. I thought it was fixed after removing the intake 3 times to resolve an intake leak but it has returned. Mine also idles at 800-1000 rpm and I have the Theo tool and don't have any codes come up in the LH. I've replaced Temp II twice and O2 sensor but I think mine started when I replaced the MAF with a rebuilt one from Injections labs . I would like to eliminate it but I have not been able to get someone to lend me a MAF nor do i have anyone close by to a swap out. I am going to again check to see if I have developed a possible air leak by using my smoke tester, but I am doubtful.

968/92

Can you confirm that disconnecting the Temp II while engine running has no affect at all?

Taguid

I'll give it a try and report back.

968/92

Pulled the heat shrink on the battery ground cable. There is some corrosion but not much. Could this cause trouble?

polcan

In my case with same symptoms turned out to be faulty LH . Got it rebuild and my 1988 S4 got wings back.
Went thru complete top end refresh ,wires . If you have access to hammer tool it will show faulty codes for idle control valve.
Scan your LH !!!!!! And save your self a lot of time guessing .

Taguid

I removed the temp II sensor while running and it continued to run like when it was plugged in. Now I did get a check engine light in the dash but after plugging back in the check engine light went off.

Mongo

If it ran the same after unugging then perhaps it may not be the sensor?

Is there any 928 owner close to you that you can swap LH ecu's with? This may rule out a faulty LH of it runs the same.

You can also clean the LH and EZK grounds at the back of the engine, under the airbox. IIRC you may have to pull the fuel damper and regulator to get to them with ease. Clean grounds give better signals and you'd be surprised what a clean ground can cure sometimes.

worf928

You've checked TEMP-II resistance at the LH and EZK pins. Have you checked the pins themselves? On the connector and on the ECUs?

The TEMP-II is the only sender that is used to trim fuel based on temperature.

Let's assume that there are no TEMP-II issues (barring poor pin contact at the ECUs that seems to be the case.)

Then, you - it would seem - are getting extra fuel from somewhere.

Have you checked the vacuum operated fuel pressure dampeners and regulator for vacuum integrity? If the rubber diaphragm in any of the three has split, manifold vacuum will suck fuel through the vacuum lines into the airguide/throttle body.