anything that raises compression pressure will cause pinging. i.e.-too much heat from wrong fuel, wrong timing, mixture waaay too lean. also, any carbon built up on the heads of the valves or the tops of the pistons physically changes the compression ratio. i read what you tried, so the sea foam, fuel grade. etc. should have helped in some way. dumb question-does the car have egr? if the egr is open all the time or when it's not supposed to be, that drives the mixture lean and raises the actual temp in the head. good luck, chuck.

How about the O2 sensor? Might be running lean.

RPM sensor??

Transmits a high frequency signal, has a shielded cable similar to TV coax. When the shielding breaks down things go funky. Also the sensor could be loose in the mount hole; rocking around sending false data re. crank position.

This may not be the cause of your problem but if the sensor + cable are original you're in for trouble if you leave the old one there.

Look in the 700/900 FAQ, from the dropdown list at top of these pages. Once there, scroll down the page to the table of contents. It's under engine sensors.

Second idea -
Throttle position sensor? Located on firewall side of throttle body. Adjusts via large slotted mount holes. Maybe needs to be adjusted so computer knows what's up? I think it only detects closed vs. partial vs. full throttle, but maybe it's worth checking.

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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.