timatt

'89 C4 57k miles.
When decelerating while in gear, clutch engaged, foot off both the gas and brake, engine braking occurs as expected for, however as RPMs drop the car will momentarily speed up - like a slight throttle blip - then continue decelerating. If the RPMs are high enough, I might experience 3 or 4 of these slight throttle blips even though I'm not touching the gas pedal.

Can this be a problem with the ISV??

Vandit

Are you running the heater?

dfinnegan

Perhaps the idle microswitch is making, and breaking, contact?

Andy Roe

It could be a broken throttle return spring or sticking throttle cable? There should be a spring that returns the throttle back to idle once you take your foot of the accelerator. Perhaps if this is broken, the throttle isn't returning to idle properly.

If you look in the engine bay it's a spring next to the end of the throttle cable. This set up is only on the earlier 964 engines and unfortunately I don't have a photo of it to show you - maybe someone else will!

tbennett017

+1 IMHO... this sounds right. With the car off, you can listen for the microswitch to click as you move the throttle on and off idle. I'd check that soon.

August West

Seems like you could rule out the idle microswitch if you do your usual engine braking but keep the throttle slightly depressed, as if you were attempting to run the engine at 1000 rpm or so. This would keep the microswitch from activating and if your car still behaves poorly, then you can probably rule out the microswitch.