MainePorsche

Guys,
I have a perplexing issue here.
When starting the car (in AM for example), she wants to stall. RPM goes down to 333 (2nd line) the surges back up to 666 (3rd line). It goes back and forth with this until she either stalls or I apply some throttle. If I do the 'two footed' pulling out of garage and drive it for literally 3-5 mins until warm, then it is all back to normal at approx. 666 idle. Car has full power. No missing to my ears. She will then drive flawlessly and restart/idle on the dime until she sits.

This issue seems like it wants to occur in proportion to how long it has been sitting. If I drive it, park it for 1/2 hour she'll start right up and idle normally. If it sits for an hour, 'seems' like it wants to lose idle rpm. Sits for two hours, 'will' lose some idle rpm until driven. Once it's up to snuff, she'll idle smoothly at 666 (3rd line). Actually the car sounds great other than this cold idle issue.

My Temp II Sensor is 1.70 Kohm cold and 290 ohm hot. This was examined 8/25/12 per my log.
MAF pins 3 & 5 have 4.2 ohms
MAF pins 3 & 6 now at 800 ohms (WSM says spec. is 0-1000). I've adjusted initially to 380 per John Speake's website information and starting up idle was abominable. I increased it incrementally until the best cold starting idle was obtained at 800 ohms.
Fuel pump not 'noisy' and performance is good. Vacuum and the hose/lines to the regulator/dampeners fine.
Put on a new fuel filter today and still with issue.
Did the little WD 40 to ISV with no significant resolution.

This reared its head about 13 month ago with the above described fluctuation in idle at cold start but it has now gotten worse, and will stall if I don't intervene. Did a Search and John Speake mentioned in a thread that the fluctuation speaks to a functioning LH ECU. Back when it started I had posted about it. Stan's recommendation of Techron and MMO did help considerably.

I find it really odd that once warm, or driven a bit, you would think she functions flawlessly. As I have this issue, I know this is not true. Questions/suggestions ?

Thanks in Advance.
Craig

Mrmerlin

Check the coil wires for shorting along the run they shouldnt touch anything,

get the MAF checked / rebuilt ,

replace the 2 plastic hose connectors that plug into the MAF boot sides

install a new O2 sensor use factory parts here.

MainePorsche

Thanks Stan.
Coil wires free. Beru's were next on my list. The O2 sensor will be factory.

timbuktoo

could it be a battery or electrical power issue? in the winter I get a similar issue and I have to keep it on a battery charger if I let it sit for more than a few days, and even then I have to revv it a bit before I can drive it otherwise it will stall just about immediately...

I noticed a similar jumpiness (although from like 2000 to 1000 and back) a few miles after I blew off my alternator (and stupid 17yr old me didn't realize until this happened) when I put on the indicator and the engine worked properly (at 2000 rpms) only between the flashes and dropped to 1000rpm and almost stalled during the flashes, only to revive its self when the indicator switched its self off again.

but this could be just a load of BS...

MainePorsche

Battery 2 years old and cells continually monitored and serviced by me. Electrical system very well maintained and monitored.
Initially I thought it was fuel starvation with a good pump. My existing Beru's are old and were next on the list. Time for new plugs as well. I do note a lot of carbon.

timbuktoo

um sorry for the newb question, but what is a beru?

MainePorsche

No, no - just my laziness.
Beru cables are the spark plug and coil lines with the 928 fittings. They're supposed to be the way to go.

timbuktoo

oh. way simpler than what I was expecting... good luck fixing your idle though.

MainePorsche

Thanks very much.

ajricker

I had the same issue with my car this spring. I replaced the idle control valve and had the MAF rebuilt. Problem solved.

John Speake

Is your car a cat equipped car ? Or even with a cat delete are you still running closed loop with a NBO2 installed ? Then no mixture adjustment is possible.

For an O2 equipped car, during the warmup period the O2 loop is disabled and fuelling is dependant on the MAF being in calibration. How many miles on the MAF ?

If more than 80k, then Louie Ott can measure it with his flow jig to check if it is the problem. See my sig.

Bill Ball

I didn't know you could adjust the MAF resistance on S4s with an O2 sensor and cats. I thought that was just S3s.

Oh, I see that while I was typing, John jumped in.

MainePorsche

Bill and John,
Greetings. Let me first say that whenever you post on 'any' topic I always stop to read, and learn. I consider you both two of the many Masters here.

That being said, let me tell what led me to believe I 'adjusted' the MAF.
First, I remembered that on the inner folder of my PO's work receipts there were two sets of instructions. The first was how to disable the remote alarm system installed (due to subsequent gremlins I completely removed it). The second instruction was how to pass smog check by turning the MAF adjustment hex key 1.75 turns CCW (to leaner).

As I began Searching (and researching) to address my cold idle issue, I began reading the WSM sections on MAF pin testing. When I posted my results, and what I 'adjusted', I had just gotten to the text where it said I should NOT have an adjustment capability.

I will admit though, turning this key CW to CO mix richer did actually improve my condition with my 'existing' problem. Aside from what my PO's mechanic wrote on the inner sleeve of the folder (PO took car to a Porsche dealership for all service), I defer to your expertise, opinions, and statements.

Regarding my reference to the 'existing' problem leading to the condition of abnormal cold idle, I think I may have found the source. The two wires leading to the Temp II Sensor had been 'dealt' with before me. The insulation used still looked good, but one could tell that someone had been there. This was about an inch proximal to the wires entering the connector. I carefully dissected and found the spliced union of both wires to be suboptimal. They were crimped into butt end connectors with bare strands still sticking out - they were barely holding on to contact. It was late at night, but I re-did them in my fashion. Next morning when I started her cold she fired right up and held a perfect non fluctuating idle. She was specifically tested when cold two more times today and was just right. I will monitor. I will also look into the availability of the harness' connector end. I am not entirely comfortable with it.

Regarding my 'adjusting' that hex key on the MAF, do you think I need to do, or reset, anything about it now that I think I have found the culprit ?

John Speake

The hex adjuster on the MAF is never connected to anything in the MAF itself, unless the MAF has been modified in some unusual way. On 87> you will find there are only 5 wires in the cableform to the MAF 6 pin connector. The "missing" one is the MAF pot.

pre 1987 cars like the Euro 16v LH and US 32v LH have 6 wires in the MAF harness and the pot is connected to the LH ECU where is adjusts idle fuelling.

Non cat 87> have a remote idle CO adjust pot above the CO panel, but no provision for an O2 sensor.

So your car must be modified in some unusual way for the pot to vary the idle CO.

soontobered84

I was gonna post that the Stepson had the same exact symptoms and I found it to be the Temp2 sensor, but you already found your issue to be Temp2 related.
Good Luck.