jmesh

I've checked the previous threads but can't find what I'm looking for.

I'm having an odd idle problem that only happens when the engine is fully warmed. Normally, my engine idles at around 850. About 50% of the time, the idle will begin to increase, up to 1500 or 2000 rpms. A quick blip of the throttle drops the revs back to normal.

I installed a Steve Wong chip last fall and the car has run fabulously. This idle problem began after the most recent oil change (done professionally), about 200 miles ago, and the oil level was right at the upper notch on the dipstick. I haven't gotten a good look at the throttle cable but it doesn't seem like it's sticking.

Thoughts? ISV? Throttle cable? Maybe the car is trying to tell me to speed up?

Thanks.

Jason

paranoidandroid

Start with cleaning the ISV and checking for vacuum leaks. Had a similar issue on my 993 and cleaning the ISV fixed it right away.

Unrelated to high idle but i think filling up to the upper notch is too much oil, especially if the tech was checking the oil cold. Check the oil dipstick at temp, and it should be between the 2 notches.

cjoenck

Erratic idle could be a number of things. I would check:
- Idle contact switch. Easy to test with a multimeter.
- Clean idle speed valve on top of engine
- Check cylinder head temp sensor
- Oxygen sensor check
- Vacuum leaks
- Airflow meter electrical connections and movement
Hope this helps.

Normandy 964

I had this problem years ago on my 944 and there seem to be quite a few threads about high idle on the 944 forum.

The general consensus appears to be :

• Check vacuum lines and gaskets for leaks
• Check the throttle position switch (On the 951 oil manages to seep into the TPS)
• Clean / Replace ISV
• O2 sensors

jmesh

Thanks for the suggestions.

I'll check the ISV first and see if that does it. Vacuum lines and gaskets were, supposedly, changed last year.

Agreed that the upper notch is high on the oil fill. My mechanic specializes in air cooled Porsches but may have had an off day.

Ecosse911

I had a similar issue on my recently purchased 964. The car drove ok initially but then developed an idling issue, where it would start hunting for idle after start up and sometimes stall when pulling up to lights. So I removed the ISV and cleaned it with carb cleaner, reinstalled and the car immediately idled without hunting. I was so happy for a day and then the car started doing the same hunting. I should mention that during this time that the oil was registering just above the upper level on the dipstick and near the top on the dash gauge. So I drained out about 3/4 liter of oil and got it reading just below mid way on the dip and same on the dash gauge. I took out the ISV again and cleaned it but it was still really clean. I also decided to clean the AFM barn door just for good measure. Lastly I recall doing some kind of DME idle reset where you turn on the ignition for a minute or two without starting, then off and then back on and start. Anyway that was a month or so ago and the car has run flawless ever since. I am convinced it was related to the slight oil which resulted in misting into the intake - ISV. The good news is that it is a quick and easy job. Good luck.

jmesh

Thanks Ecosse911. That sounds exactly like what I'm getting. Checking the ISV and barn door. Fingers crossed.

I'll update the list when I know more. Thanks all.

jmesh

I realize I never replied to this.

The solution was exactly what Ecosse911 suggested. My mechanic had a bad day and overfilled the oil slightly. Draining a little out did the trick.

Ravioliv

Hi all
Thanks for various comments
Still waiting for engine to be opened as I gave the go to investigate cylinders condition.
Indeed suspicion is primarily around the piston rings
Infos that were not provided are that engine has been runnin a MAF set up for at least 10years.
Engine rebuild was done by my father who is a former mechanic and after the rebuild car was dyno with pretty good numbers.
Oil consumption and analysis are not easily available ( because oil is new and quite low yearly mileage like 2-3000/ year )
Vaccuum lines and ICV I checked extensively and I really don t think anymore that is the issue considering the high amount of blow by visible on the dipstick + hose going to intake.
Another strange phenomenon is also this oil backflow at the oil filler neck
All that points toward pressure in the oil can….
And yes I know “how about the breather?”
Breather is fine in the sense it is clean and spring operates normally….but also breather is really small so I can imagine that there might be some kind of pressure build up …

Valves clearance has been checked and adjusted twice…

Otherwise as it was asked my car is a 1989 version so with aluminium manifold.

The only remaining doubt that I have is that “one day” that is somehow matching the period where I started to notice the idle issue, when lifting the car with the jack without enough care, it put an effort on the oil thermostat ( near the jacking point ) , to a point that there was a bit of oil coming out from the lower hose.
I immediately released the jack, wiped the oil, checked the clamp position and tightening , check any possible damage or deformation and really nothing was noticeable so I concluded that is just forced open the hose connexion under the oil can…and stopped sweating….
Since then ( and we talk about 4years , several track days) no issue regarding oil leak, pressure or whatshowever…., thermostat opening noticeable on the dash needle, temperature normal…)
I kept wondering what could have gone wrong with this “mistake” but could not find any cause / effect hypothesis, neither could my mechanic who is a well known porsche specialist that I trust well….

Showing the thermostat and jack effort was applied on the drain plug, but with part of the jack pad correctly in contact with jacking point, so to me effort was limited