Merle

My car is doing the exact same thing. I cleaned the iac valve and it didn't help much. Ironically my Ford F150 was doing the same thing yesterday and I pulled the iac valve and it was gummed up pretty good. Cleaned it with some Carb cleaner and it totally fixed it.

sml

could you flick your wrist holding the icv and hear it rattle?

Havana Henry

I don't recall, it was a while ago. Does that mean it's knackered then?

Should be able to get to it tonight.

J richard

A few fundamental things to check:

1. If you have a LWFW it's a systemic issue, if not it's solvable.
2. Make sure the idle control microswitch is not being held open by a loose carpet pad or a misadjusted throttle linkage. You can check by cracking the throttle plate and listening for a click right hand side of the throttle body. This is really a common symptom.
3. Check vacuum leaks, including the oil cap and bteather tubes going to the oil tank, if you take the cap off and there is no change in idle you probably have a pretty good leak. I've seen cars with the vent line split 4" down the side, completely driveable but with frustrating idle issues.
4.Change an old O2 sensor.
5.As mentioned check for an intake leak at the FI boots, throttle body and the injector Orings, don't overtighten the band clamps! Just snug them.

Usually there are a number of contributing factors, frustrating but these are 20 year old cars after all...

Good luck!

sml

if it is clean, then it should rattle as the little gate on the inside opens & closes.

even better ... connect a small 9V battery and it should pop open.

sml

Just dug this up from an old post of mine ......

"Quick update because I have solved my problem.
I think I have read every thread on 964 idle problems.
There were 1 or 2 people that said their car never idles correctly until a Bosch Hammer system adaptation.

The majority said that the battery disconnection technique was the same as the Bosch Hammer system adaptation -> this is definitely incorrect.

To try to resolve the idle dipping (I may or may not have a LWF), I have tried:
- new ISV
- Steve Wong chip
- new coils
- new fuel filler neck & cap
- checked for vacuum leaks
- new air filter
- cleaned AFM
- fuel injector cleaner fuel additive
- new oxygen sensor

I have tried the battery disconnection technique 20 or 30 times ... when cold, when hot, idling for 10mins, spirited drive for 10 mins -> waste of time.

The car continued to have an idle dip whenever the revs dropped.

Today I drove to the mechanic with the usual minor slight idle dipping.

Carried out Bosch Hammer system adaptation.

I drove home without idle dipping! After 1 year it is solved!

Havana Henry

Well, checking all the above and the ISV are free so I'll try them first at the weekend. If no joy, it's off to get hammered!

Thanks for all the input guys, I'll report back when I get a result.

Havana Henry

Just carefully checked the service history and the clutch was last done 30k ago with a dual mass flywheel, so it's no lightweight job.

CBR786

I am in Birmingham UK have Porsche system tester and can so system adaptation for you problem is you are too far away otherwise I would not mind helping. I always do a adaptation everytime my battery goes flat or I disconnect battery. The problem is I am working alot on my car and nearly always disconnect battery for safety hence I have to readapt the settings.

Bud Taylor

Look at what is happening mechanically. Mine was a cable adjustment and I had tried all the other list fixes including cleaning the isv, actually put a new 02 sensor on (plus installation cost).

Just like bicycle cables, throttle cables stretch over time causing them not to make solid contact with the microswitch in the closed or no throttle position. Fiddle with the throttle linkage to make sure it returns to touching the microswitch when not depressed to return idle to normal

Havana Henry

Thanks for the kind offer CBR, but as you imply, I reckon the fuel cost alone of a return trip to Brum is more than paying someone down here to do it.

Thanks Bud for the tip. Hopefully out to the garage soon.

Jacke2c

I am not sure if this helps, but I have been having the same problems on a sporadic basis. I drove my car on ramps 2 weeks ago and discovered where the throttle cable emerges from the shft tunnel (where you are supposed to make cable tension adjustements) that my cable end had "jumped" and the cable sleeve was cought on the grommet end of the housing, just holding the cable ever so slightly tighter than it would have been if it was seated propery. I had only discovered this because I could not get the idle switch to close because the cable was tight. Once adjusted, my car idles beatifully at 825 rpms.

HOWEVER, what I think caused this is: I beleive i have a bad transmission mount. When I ocme around a curve ifn fourth gear in town and am ******* the engine at 600 rpms in 4th gear and pulling away, I both hear and feel a strong clunk (sometimes 2) ....No, I just bought "new" WEVO w/Blue pillows.
So tommorow, i am back under the car to see where the play is coming from... Jack