Jeff928S4

1989 S4

Cold start problems (have to keep foot on gas to keep idle or it stalls)......once car warms up, slightly high idle....but runs fine.

MAF is re-built.....LH re-built.....I suspect TempII sensor.

Can't seem to locate one locally and was curious is there was a Temp sensor from another make that might fit or do I need the exact Porsche Temp sensor??

Thanks!

RyanPerrella

autozone sells them, but it may take 2 days before you get it.

I would first suggest the TPS sensor. When you move the throttle at the intake from open to closed do you hear a click? If not then the TPS is the first place i would look.

Try the temp II sensor, i replaced 3 things at once on mine so i cant confirm exactly which one did it for me

RyanPerrella

also do a search for "rock steady idle" in a thread started by me. You will get information on the autozone parts.

Cheers

heinrich

https://rennlist.com/forums/928-forum/369455-ive-finally-joined-the-rock-steady-idle-club.html

Garth S

Jeff, You have email response .. on issues for those who may have hosed down their engine as part of the wash programn

Do this check recommended by Wally if you suspest the throttle position switch.

08-05-2007, 11:50 AM #10
WallyP

Rennlist Member
--------------------------------------------------------------------------------

If you have a late S4 with the digital display, you can make a quick on-the-road test of the idle switch.

Put instant MPG on the display. On a long hill, lift your foot completely off the throttle pedal - as long as you are coasting at more than about 1400 RPM, you should show 90 MPG. If not, the ECU isn't getting the idle switch signal.

The ECU completely shuts off the fuel at over about 1400 RPM when the idle switch is made...
__________________

RyanPerrella

thanks for the link H

VehiGAZ

Here's a great write-up on how to test the sensor with a multimeter before you go and replace it...

http://www.electronikrepair.com/wst_page9.html

Read through that, but then go down to the bottom of the page and check the links to the LH and EZK connector diagrams. Piece it all together... you can test the sensor resistance from these connectors to ground (pin 13 on the LH; pin 19 on the EZK), which will let you verify the whole circuit, instead of doing it piece-meal. And it's a lot easier to pull the two computer connectors off than that damn sensor plug!!

I just tested mine last weekend this way and found that I have to dig deeper to find my idle problem. This weekend - it's MightyVac's turn! If that doesn't find a problem, it's a plenum rebuild over the winter...

Good luck!

Jeff928S4

Garth...tried Wally's test.....but my digital display is "Canadian", so it's in Klms...and when I lift of the throttle, the reading slowly counts down from around 38mpg down to around 15.....like I assume it should.

ROG100

Sounds like your TPS if you do not get the 90MPG or the equivelant metric readout.

Jeff928S4

The car runs pretty much normal at 75%-100% operating temps.....on start up....the throttle may need a flutter to get the idle correct and sometimes it is idling at around 1000-1100.

When it is at a 50% or lower operating temp, the car seems to be running on half the engine and doesn't feel like its is getting the gas correctly.....the pedal has to be held to keep it from stalling...but once it warms up, no problems.

The MAF and LH are new.

Would the car run ok at high operating temps if the TPS or ISV are bad? I had a bad idle stabilzer valve in my 944 and the idle would always "hunt". Usually I had to keep the gas slightly pushed at stoplights to keep the revs up.....and this was at full operating temp. The 928 seems to work fine once it is warm?

Pardom my ignorance, but where is the TPS located? I know the ISV is under the intake, but what about the TPS?

Rob Edwards

Here it is (black box with the 3pin connector). Unfortunately you'll note that the intake is A) disconnected from the car, and B) upside down:

Jeff928S4

Damn! It looked so accessable in that pic.

Rob Edwards

I have the same idle issues when cold (but it's stable at ~1K rpm when warm), and just did an intake R&R with a new ISV, TPS, rebuilt MAF and LH brain. I think I failed to index the TPS on the throttle shaft properly, my gas gauge only gets to about 60-63 mpg when idling down a long hill. I will verify by checking the pins at the LH and EZK connectors, and then the intake's coming off again. Should be much quicker the 2nd time....

Jeff928S4

I don't get the digital display idle test?

If you are getting, in my case, 38-40 klm/litre and let off the gas....why would it shoot up to a higher number? Mine just acts like it is working correctly - i.e. less gas being used, the lower the number on the display.

What am I missing here?

Rob Edwards

The higher the #, the better the km's per liter, or the LESS fuel per distance you're traveling. With the TPS idle contacts closed, you ought to be getting the equivalent of 90 mpg. ( which = 37.53 km/l if my conversion is correct)

So if you're showing 38-40 km/l, that would be 90 mpg, or the max it'll show. So maybe you ARE getting the idle signal from the TPS?

Maybe your hunting idle is not the TPS's fault, maybe it's something else- O2 sensor, vacuum hose leak, ????