John S. Markowitz

I'm trying some final things before concluding the intake is going to have to come off my car (Again),,because of an instable idle and even stalling at stops. (Its running great on the open road)

Anyway, so I've cranked the car cold, disconnected Y pipe that leads under the intake to the ICV and sprayed copious amounts of WD40 down the hose into it, quickly gunned the throttle a number of times (which of late can put the car into very low idle or even stall it while it us parked or at a red light). I repeated this many times.

This intervention seems to help it regain a steady idle. However, as soon as I plug the Y connector back up and the system is closed, it seems to revert to the wavering idle and near stalling again.

What does this tell me diagnostically? Amything??

John

1991 928 S4

davek9

What is the vacuum # at idle?
What is the AFR reading (need a wide band O2)? a test rig can be used and inserted in tali pipe.

Running great under load indicates a vacuum leak or too rich, and the ECU's are attempting to compensate for it.
Why was the Intake off the first time?

Dave K

John S. Markowitz

Hi Dve

I don't have a means to determine those numbers you ask about..
The intake was just removed to do a "refresh". This problem did not exist prior to that.

John

davek9

OK, vacuum is easy to check, Auto stores may even loan you a gauge, just attach to a vacuum source (like the front Fuel rail damper) it should vary with throttle.
Don't understand the WD-40 thing if you already replaced it (it's new).

You most likely then have a leak, lose hose or poorly sealed intake.
Other things would be TPS signal not getting to ECU's, bad O2 or signal not getting to ECU's, incorrect TPS setting and or a leaking vacuum unit(brake booster, HVAC, etc.(most of them can be blocked off for testing and the engine will still run.

Good thing is you just done it so a redo will be easy

Dave

Christopher Zach

Wait, have you replaced the ICV yet?

The ICV is basically a motor of sorts that can turn a bit one way, and a bit the other. The controller puts a current through the two magnets, and the valve lines up with it to set an idle.

Those magnets are on the armature, and have commutators and brushes. Dead spots appear on the commutator, and the brushes wear down. No amount of WD40 fixes that.

I'd say replace the ICV if you haven't with a real genuine Bosch one and be done with it. I did this myself, even bought a $25 Chinese knock off that wouldn't even plug into the harness. It was junk pot metal.

chart928s4

Have someone use the Bosch Hammer on it. Takes about 5 minutes and should tell you if there's any malfunction in the ISV, TPS, O2 sensor etc and provide clues if it's a vacuum problem. Not sure who the Florida 928 mechanics are but even a 911 guy might have one.

worf928

SeanR

Hammer owners should have both connectors

worf928

SeanR

Me wants that. I've only seen one in orange.

worf928

chart928s4

Multimeters are definitely plenty useful and so is that great inspection guide, but the OP has a '91 so he should have the round job. I was very pleased with the decisive instant (orange Hammer) diagnosis that said: You messed up the intake refresh. TPS not properly positioned/clocked was the problem. It saved a lot of random disassembly, head-scratching, and uncertainty. BTW - symptoms sound exactly like mine (choppy stalling idle but OK at speed) but there can be many other causes.

Shameless plug: That is one of the many reasons the ~300 imported US '91s are the rarest and best S4s.

SeanR

'87's wont store codes (unless you have a JDS rebuild) but you can check everything function wise.

worf928

John S. Markowitz

Hi Dave

Thanks for all those suggestions- on the WD40 thing- the idle control valve was unfortunately NOT replaced with the intake refresh - so I'm trying to avoid having to remove the intake again. This is not a DIY project for me by any stretch!