GRUWEZ

Hi all,

I got my 1993 964 C4 Cabriolet out of hibernation this morning. The car started fine but when the engine was warmed up, idle speed became erratic. It fluctuates between 600 rpm and 800 rpm with engine oil pressure fluctuating accordingly. I drove the car for another 10 miles, warming it up and chasing it through the revs when it was fully warmed up. When I came back home, idle was steady and I already counted my blessings. But after I switched the engine off and switched it on again (so the engine was still warm), the erratic idle problem was there again.

Any idea what could be wrong?

power_up

A hammer adaptation can be a tried?

GRUWEZ

Please enlighten me, what is a "hammer adaptation"?

The funny thing is, I drove the car a bit more and the problem has completely disappeared. Still I would be interested in a cure, in case the erratic idle reappears.

Thanks!

napaul

I just went through this a couple weeks ago...for me since I don't have the hammer scan tool to do idle adaptation I was given the following advise which so far has cured my problem.

Unplug your battery for a couple hours ,plug back in and start the car. Do not touch the gas and allow the car to reach operating temps at idle and then take for a drive and take it through the rev ranges. You could also check your idle micro switch to see if it is working I sprayed mine off with some cleaner, you could also try to clean your isv valve, these are all cheap solutions to try first.

GRUWEZ

Thanks! I know where the ISV is. Where can I find the micro switch? Yes I know, it is a newbie question

James Achard

If the car has been sitting for a while it could be bad petrol. Run the tank almost to empty and refill.

Cheers, James

sml

Caveat... this does NOT work for many people. Get the real Bosch Hammer.

HiWind

Bump for this question PLEASE! Thanks!

PNine64

Sort of behind the ISV muffler.

HiWind

Aha thanks - I think the issue might be how modified this 3.8 is!!
I don't think I've got a isv muffler lol

HiWind

Another pic ... Don't be too concerned as the 3.8 required a fuel mgt system
And while I have yet to work out where/why everything is, the car runs well save for the idle issue that comes and goes.
Today the intake manifold blew out of its moorings - rubber rings and clamps - but after a quick 5 hr strip down
It is now clean, srubbed in petrol and well seated with new (socket head) clamps instead of the screw kind (kuk).
Bit of a mission to tighten them tho as you need to go slowly and iteratively else the intake gets pulled out of the rubber seats
AMHIK

Anthony Hutt

Had a similar problem and after fully charging the battery with a trickle charger the fluctuation at idle when starting a cold engine or starting up after a short trip has gone.

sml

for the 5 minutes it takes, i'd still try a system adaptation .. most people seem to report improvements.

HiWind

I have a brand new battery - i'm quite sure that'll not impact.

ps - why are my pictures upside down now?!

elbeee964

I had this fluctuating idle problem for a couple years after buying my car back in '06. Mystified the hell out of me. I chalked such to an aftermarket air flow sensor and chip that came with the car. But reinstalling the stock components resulted in no change.

Tried everything, then found out the cause when I hooked up a Scantool (a Bosch Hammer or Durametric would have shown the same).

At 'idle' -- accelerator not depressed -- my Idle solenoid (on the throttle body) was not being engaged. My throttle line was too tight.
I loosened that cable a bit via the throttle cable adjustment nut just ahead of the transmission body and... everything's been great since.
A rock solid idle of 820-850 rpm all the time, every time.