gamut200

Hi guys,
After years of contemplation I finally decided to buy a 928 GT!!
She does however have an intermittent idling problem. Occasionally it will not hold idle and die on me at a traffic light, other times the idle will surge anywhere between 1000 and 2000 RPM. From the bit of research I did the starting place appears to be the idle control valve that may have some dirt in it. There is a very good write up on spraying some WD40 into the pipe leading to the ICV. This write up is however for a LHD car – mine is RHD with the brake booster on the left hand side rather than the right had side so just wanted to make sure I am doing this correctly….

(Just a bit of info on the car – had a minor service a few hundred miles ago. Diagnostics run by indie just before I bought it with no fault codes. He did re-tension the cambelt so maybe something was not re-fitted correctly. The PO said he had no idle issue at all)

Anyway below picture of the right hand side of the engine bay.



Should I just loosen the fitting and spray WD40 in the direction of the arrow or am I getting this wrong for a RHD car.

I also include a pic of the LHD in case I need to do this from the opposite side

Any help and comments appreciated to get my shark idling smoothly!

chitown928s4

Check both wiring looms going into the computer box next to the CE panel. Remove and check for moisture. Mine had water dripping it was pretty bad. No more car washes for me.

ROG100

Welcome to the shark tank.
That is the correct hose to spray WD40 down - give it a good 3 to 5 second blast. Preferably with a pipette on the spray bottle. Let it sit for an hour and then start the car.
Judging the state of the engine you may have other issues such as knock sensors not working and a inlet manifold R&R may be in your near future.
Roger

Hilton

Yep, Roger's correct, its the right place to spray.

First though, check the idle contact switch on the throttle switch is clicking when you move the throttle by hand (engine off), and then check that the signal is reaching the LH connector by checking for continuity at the pins 2 and 6 (see pinout below for the LH ecu connector - its the ECU nearest the outside wall). WHile you're in there, check the full load switch too.

If the throttle cable is too tight, then it could be borderline on the switch and engine expansion causing it too unclick off "idle" position.

What year GT? UK didn't get cats and an O2 loop until 1990, so if its an 89 GT then that rules out O2 sensor issues.

gamut200

HI guys - thanks for the feedack.

Hilton, the GT was registered in 1992 so probalby one of the last produced in 1991.
I had the car at JDS porsche last weekend and he ran various diagnostics - no obvious fault codes.
ICV appears fine and the "clicks" under test
Ran a vacuum test and pressure is ok (not perfect but should be fine - did not write down the specs)
Full load is defective - John recons this will only be an issue under full load and I should replace this when inlet manifold is off but should not affect the idle.
We could not get the idle reset/actuated using the diag tools. John plugged in another LH unit and we the diag tool could reset the idle. I did not take it our for a drive with this LH unit, but this appears to be the issue so will have this rebuild next weekend unless I can find another possible cause for the car not idling
I am not too technical, but should I try and cut out the O2 (if possible) to see how it runs - as far as i remember the diag tools did not check the O2

ROG100

You are in good hands with John.

gamut200

He is a great guy and spend a good hour with me running varioust tests on the GT so I can highly recommend him for any shark owners in the UK / Cambridge area. Once i get her running smoothly I will address the state of the engine bay - really looks a bit un-loved for but she runs like a dream once on the open road. Took her out (to JDS) for the first long run last weekend and got an average of 25 mpg on the way there and 23 on the way back (at licence losing speeds on open stretches... just could not resist!)

NC928S4

Your symptoms sound very similar to what I encountered early on. Idle had more difficulty when ambient temperature climbed into 80-90s F. Checking and cleaning all electrical connections and grounds and WD-40 spraying ISV helped. The Temp Sensor II ultimately was the fix. It failed the resistance tests so I swapped it out and idle problem was fixed.

gamut200

We did check the temp sensor II and resistance was fine....

MainePorsche

CO/idle mix adjustment ? Does your exhaust smell rich or lean ?

John Speake

Mixture seems fine, this is a late car so has cats/O2 sensor. The LH ECU swap pretty much confirms the problem lies there.