MrLexse

Okay, I'm just about ready to reinstall the intake manifold / throttle housing after disassembly, powder coating and re-assembly, but before I do, I want to find out if there is a testing procedure for the idle control valve and / or throttle control switch. I looked in the WSM and found nothing (except a picture or two). I don't remember the engine having idling issues before taking the manifold off, so I'm going to assume they're all right, but if there is a test procedure out there, now would be the time to find out about it. All help is appreciated.

fraggle

I tested my ISV by just attaching it to 12V and actuating it. Made sure to clean it and soak it in WD40 first.

StratfordShark

I could operate ISV through full cycle just by attaching to little 9V rectangular battery. Of course listen for "clunk" but you can also watch shaft and verify it rotates from full open to full closed.

The TPS can be checked just by listening for click off idle, and meter on contacts will confirm switch closing at idle at WOT. Seem to recall some post about the wsm identifying the relevant contacts of the switch wrongly? Anyway it's a cheap fragile part prone to breaking, so maybe best to replace with new.

Tails

Purchase a set of David Moorehouse's technical CD from Rogern at 928sRus. This will be the best purchase you will ever make to assist you in maintaining your 928.

In the Tech CD are two great documents, as well as the WSM and the electrical drawing for every model of the 928:

"LH-EZK-Diagnosis/Troubleshooting" and "928S4 Test Plan EZK-Ignition and LH-Jetronic '87"

These will tell you how to test the ISV and in addition the "search" section on Rennlist will be your best friend in the DIY world of 928's.

I you want to go the ultimate route you can buy either a Bosch Hammer, a JDS Spanner from John Speake or a DT928 Diagnostic Tool from Theo Jenniskens & Paul Moers.

To put the icing on the cake you can convert your PC notebook into an oscilliscope and check out the wave forms of you sensors etc. See the post of today regarding "injectors not working/no start" and there is a description of how to convert your notebook to an oscilliscope.

The final step for now is to down load a free copy of Alan Moore's "Porsche 928 Wiring Diagram Primer" by googling it and you will be able to read the electrical drawing for MY87 through to MY 95. It is an excellent aid to all electrical drawings.

Happy DIYing.

Tails 1990 928S4 Auto

SeanR

I also use a 9v battery to test them.

Now is the time (as mentioned by StratfordShark) to replace the TPS, they all fail, so save yourself some time and get a new one.