Hi everyone,
I just recently got my car back from the shop with an exchange engine installed. The "new" engine had 87k miles, the shop rebuild the lower unit, timing belt, water pump and used my old intake and fuel harness to put it all back together.
The idle stabilizer looked well, I thoroughly cleaned it (WD40) and they reused it.
The car ran great for about 1500 miles (it's my daily driver and I run it pretty hard for about 120 miles a day, I had to give my S320 to the wife...) and just yesterday started to idle a bit rough. The idle RPM dropped from 650 to ~580 and it noticeable fails and even stalls once in a while. It runs OK when started cold and runs at about 600 when I run it for a while. If I turn it off at operating temp and then back on after a short stop it barely runs. Once I take off it seems to have full power, no smoking or any other greatly concerning signs.
Did my idle stabilizer die or could it be something else? I remember getting the car back after a timing belt change a couple of month ago with a very similar symptom, the shop re-adjusted the timing and it went away.
I hope I don't have to take the whole intake back off.
Regards,
Sab. <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />

 

Read my comments under the topic above...."runs good on techron 88s4"

Try a good stong does of injector cleaner.

Hawke <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

 

Good idea, I'll try that even though I just got new injectors. I noticed a fuel smell in the car when sitting in traffic as well.
I guess this is going to take some trial and error procedures.
cheers,
Sab. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

 

My stock answer - vacuum leak

Possibly the timing advance vacuum hose to the distributor is loose/leaking or other vacuum related problems associated with the intake or the warmup regulator.

It certainly also could be your idle stabilizer as you suspect. If so, it can be cleaned to give it extended life.

Let us know what you find.

 

Uhhhhh....

The S4 motor engine management has no 'vacuum advance' on the distributor(s) - all electronically controlled based on several sensor inputs.

Gas smell may be from the infamous 'Y' connector to the charcoal canister located in the Passenger wheel well.

Idle problems can be any one of the following -

-Partially clogged/fouled injectors
-Faulty Idle Stabilizer
-Faulty Idle/WOT switch
-LH Injection conrol unit about to go South.

Fixes can include-

-Bottle(s) of techron to clean the Injectors
-WD-40, or replace
-Replace faulty unit
-Replace faulty unit

The Idle Stabilizer and the switch both reside deep under the Intake. My Idle/WOT switch failed - even though the PO had replaced nearly everything else under the Intake 2 years ago. I am also replacing coolant block off gaskets and the oil filler neck gasket at the same time.

If the LH unit is dying - try Partwerks for a rebuild. Less than 1/2 the price of the big 3, and the same warranty applies (same source).

hth-

 

OK, so I have already gotten the injectors cleaned, the idle regulator was replaced 9k miles ago (along with vacuum hoses and knock sensors), the throttle position switch a little later (argh - intake out again, big $$$), and I plugged in another LH computer unit.

And the beast still gives me a free massage everytime I stop at a traffic light! It feels like it randomly drops cylinders. It does not show any unusual behavior otherwise, responds normal to throttle inputs. The gas mileage is better than the two other 928s I owned before.

It also recently got a new Y connector, in-tank fuel pump, O2 sensor. The alternator and air mass flow sensor were tested, new spark plugs and wires installed. Caps and rotors 10k miles old. Only real "old" stuff are the coils and their grounding strips, the wires to the injectors, and the rubber thingies that go between the wires and the spark plugs.

I spent thousands of $$$ already, with no improvement. We're going to check the vacuum next. Thanks to some very dedicated Rennlisters we got quite some ground covered in the troubleshooting process. Thank you guys!

Hope we'll ever figure it out...

 

OK, I did some research on my fuel smell and have quickly determined that there is some sort of leak under the tank. It's wet, does not actively drip when it sits in the garage, but the fuel pump cover is really soaked.
I took it off and got a good look at the pump and the filter.
It just does not look right, I suspect someone had it apart and put things back together the wrong way. <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />
It looks as if the leak comes from the brass fitting that connects the front of the pump to a fuel line, which then goes to the filter.
That metal fuel line goes straight up from the pump and makes solid contact with the metal mounting braket right on top of the filter. The front rubber mount holding the fuel pump in place looks very stretched, since the pump is being pushed down from the fuel line squeezed against the braket.
Can someone tell me how this should all be assembled? I would assume a fuel line is not designed to be torqued up against the braket.
regards,
Sab. <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />

 

Sab-

I recently changed my fuel filter, and when I had it apart, I noticed the same seepage. It appeared the line was not torqued down enough. I loosened the bracket holding the fuel filter and torqued down the pipe....problem solved. I put it all back together, then stapped the filter down tight.

Hope it helps...

Normy!

 

Sab:

Check out the 928 Specialists site <a href="http://www.928gt.com/928tips/Fuel.htm" target="_blank">here.</a> Pictures and all.

 

Just for the record, the brass or aluminum washers should be replaced each and every time the are removed.

No, I haven't been a practioner of my own words of wisdom. However, I did buy a couple sets of new ones for the next two go arounds (oil plug, fuel filter and pump, radiator and block plugs).

I don't remember how much, but they weren't expensive.

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Max

 

Thanks everyone for the helpful response. I have taken it all apart now and have decided to replace it all. The positive power feed was drenged in fuel as well, there are marks from vice grips all over the lines and nuts from the filter and the pump. Very scary.
I will buy a new pump, filter, connecting line and fuel pump check valve. I guess that will take care of the mess.
Would anyone recommend another part(s)?
Thanks,
Sab. <img src="graemlins/xyxwave.gif" border="0" alt="[bigbye]" />

 

To save you a little $ - I did the same thing - new pump, new valve. My pump came with a new valve, so you might want to check it before ordering.

And while you are in there, you might want to replace the screen which is in the tank, directly before the fuel pump feed line. Can be replaced from the outside.

And...make sure you have a firm counterhold on the line from pump to filter when you replace it - it bends in an instant (sad experience talking).

 

Thanks for the advice in regards to counterholding the checkvalve when tightening the line to the fuel pump. But how and with which tool? I can't get anything in there. It seems to be a 17mm wrench, but a standard tool won't fit.
Any tips?
Thanks,
Sab. <img src="confused.gif" border="0">

 

Sorry, Sab, I was referring to both filter ends - that's where I bent mine when I slipped off the counterhold.

I avoided the counterhold issue with the check valve by assembling the pump/line when it was out of the car. The nut was frozen on disassembly and pulling the whole mess was the easiest and least back-breaking method to do both the R & R

 

Thanks James,
that's what I ended up doing. Once I put it all back the fuel line moved just a bit when toquing down the last line to the filter, but it I think it is OK. It does not touch the mount and it is not leaking fuel anymore.

BUT it unfortunately did not fix the idle problem. So I guess I will try to poor some WD40 into the idle stabilizer next.
regards,
Sab. <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />