HELP! Idle problem. Air flow sensor. OBDI, OBDII Aaaargh!

[Moses]

First, the problem; I have a wildly fluctuating idle. At startup it idles well, but as soon as you touch the throttle, the idle starts to swing up and down until the motor dies. During this idle fluctuation, the motor is running extremely rich. Keep in mind this problem is new and came on suddenly. Prior to this, the idle with the Cyntex chip was rock steady at 800 RPM.

Well, my mechanic hooked up an OBDII diagnostic port to my OBDI 993 DME to diagnose my idle problem. He says it is reading the DME signal without problems. (I didn't know they were compatible).

The diagnosic readout says there is a problem with the Air Flow Sensor.

Does all this make sense? Will an OBDII diagnostic port get accurate readings from an OBDI DME or are we chasing electronic ghosts?

[Bill Verburg]

Here is some reading material for you
Fault codes
its for 964 but may help

You are going to be the expert on this and we will be asking you for help soon. For instance I would like to hook up a diagnostic port.

964 diagnostic socket

How to clean the idl stabilizer valve

Obviously all wires and grounds were checked? Vacuum leak was looked for?

[Moses]

Bill,

If this works, the OBDII diagnostic port will be a cheap solution.

So far I know there are no vacuum leaks, the throttle position sensor is OK, the O2 sensor is OK.

Hey! At least my Varioram is now working.

Right now we have to figure out if the air flow sensor is indeed bad, or if there is a wiring problem or if we are geting nonsense from the computer because the OBDII port is not compatable with the OBDI DME.

I'll let you know when (if) I figure this out.

[Bill Verburg]

Wish I could be more helpful. There is so little user info on these engines.

My idea for the diag. port was to glom one from a '95 993 at a salvage yard.

OBD1 aftermarket scanners are readily available.

The difference between OBD1 & OBDII ports is a great question.