bgibby

Here's the dealio: On my 90GT with only 73K miles I've had this re-curring idle problem that's really bugging the crap out if me. My car idles ok most of the time when cold, but has just recently started this hunting up and down thing even when cold (cold idle used to be fine). When warm, sometimes the idle will be ok, but it will die on occasion & when coming to a stop the idle drops very low & then recovers or sometimes fluxuates up and down from 500-900 rpm.

This started happening a couple years ago & since then I've r&r'd the intake (this solved a slight pinging problem I was having) with all new parts including cleaning & balancing the injectors. The intake bits were actually in great condition, but I had all the new parts so I went ahead & replaced them. This included the TPS & knock sensors- I also sent my MAF in for testing & refurbishing (it also was within spec). I've installed new plugs, rotors & wires within the last 6K miles as well & when checking the plugs they have a very even coffee w/cream coloring.

Just recently I found what I thought was the culprit. I had always checked the readings for the TempII sensor at the source under the hood & got acceptable values, but I decided to get a reading at the LH & EZK plugs. Sure enough, no reading- turns out the wires at the sensor were slightly damaged & not sending data to the LH or EZK. This was an easy fix & I thought everything was hunky dory as my GT ran like a scalded cat once again (strange how you don't notice a gradual decrease in power) & the idle was pretty good. Problem solved- so I thought.

As a side note: my idle always seems to work well after I've disconnected the battery & gradually gets worse. Well, seems my fix with the TempII sensor did not fix the idle problem as I'm having the same symptoms- rough idle, sometimes stalling when warm & now a new one where after warming up & then parking for a while it will start & instantly stall to the point I have to apply gas to keep it running.

At one point after my intake r&r, Bill Ball was kind enough to send me his Spanner & I tried running the idle adaptation along with the other LH diagnostics, but the Spanner would always stall in the middle of its operation. I'm now thinking this had something to do with the TempII sensor wiring problem.

But wait, there's more. When I bought this car, it had 38K miles. The previous owner had it for I think about 5 years and had replaced a failed LH unit already- I still have the original. I'm pretty sure he purchased this replacement from a Porsche dealer. So all this time I'm thinking (hoping) the LH is not causing my idle problem, but I've exhausted just about every other avenue.

There are definately NO vacuum leaks. TPS works perfectly. O2 sensor has been replaced. Fuel pump & filter have been replaced (don't think these would affect idle anyway).

So... I'm hoping someone has an LH I can swap into my car & see if that solves the problem. If so, I'll send mine in for rebuilding to Mr. Speake.

My business is embroidery & screenprinting & the person that affers up their LH will be handsomely rewarded with a fine golf shirt & hat with some very cool 928 embroidery as well as shipping.

Thanks in advance,

Brian

90GT, Guards Red/Lt Grey Sport Seats, Ott X, 73K
Bandon, Oregon

PS: Any golfers out there? I live right around the corner from some of the finest courses in the US: Bandon Golf Resort & the new Bandon Crossings. I'm a member at both & would enjoy showing a fellow 928'r around these amazing courses.

6.0-928S

How about the IAS valve?

Hammer

bgibby

All new parts when intake was r&r'd.

Mrmerlin

have you checked the ignition system in particular the left igniton coil wire, are both grounds on the respective cylinder head to coil mounts, was the hall sensor replaced, have you checked the fuel dampers and fuel pressure regulator for either holding a vacuum and if they might be leaking into the vacuum lines, did you replace the 4 fuel lines?, How many miles is on the idle stabiliser, you might try the WD 40 flush, check for vacuum leaks, Check the CE panel for water dripping onto from the bottom of the blower box, any corroded fuses? If you find any corroded fuses then also check all of the relays,any corroded relays open them and inspect the insides

JP Rodkey

Replace the ISV.

John Speake

O2 sensor ?

Louie928

I have a spare LH I can send to you.

Randy V

What a pal!

bgibby

Thanks, Louie!

Bill Ball

I encounter occasional cars that will not complete the idle stabilization with the Spanner and/or Theor 928 diagnostic, sometimes both, but not always. I have yet to resolve any of these failures. They just won't respond properly to the procedure even though we otherwise get no error codes and can find nothing wrong.

If the Spanner failed, I would still try Theo's 928 diagnostic. Someone up there should have it available locally. It might work. However, based on your symptoms, I don't think it's going to be as simple as running the idle stabilization program successfully. I don't know what, as you have changed out almost everything. Sure, it's worth swapping the LH for a test.

worf928

Since the LH was not seeing the Temp-II because of wiring issues, is it possible that the LH cannot see the ISV also? Since you don't have a Bosch Hammer handy, if you have JM's CDs, there is a direct test,in the FI guide, for the ISV from the LH plug. If you don't have it I can post step-by-step tomorrow.

redpathtribe

Louie to the rescue again! I'd bet this is the same LH unit Louie saved me and my GT with a few years ago when it died on the way to DEVEK days. Thanks again for that Louie (and to Marc for bringing it and coming down to save me!).

One more possibility? You said you had the MAF checked and refurbished a couple years ago now. Who did the checking and refurb? After a couple years, it could be the refurbished MAF. You may want to try swapping that out too with a known good one.

Dave H.

Louie's spare LH has been in a lot of cars...

Louie928

It's great insurance. For all the time I've carried it, I've never needed it myself. Same for my spare MAF and spare clutch flex hose. Spare tire too.

bgibby

The MAF was tested & rebuilt (even though it was not really out of spec) at www.injectionlabs.com - this was maybe 8K miles ago. I'm fairly certain there is no problem with the MAF.

The only reason the LH was not seeing the TempII sensor was a small fracture in the wiring right at the sensor itself. The wiring & rubber bits in this car are in excellent condition for it's age which is why I didn't look at the LH plug for the TempII originally- the fact is that it's easily tested on the engine whereas all the other sensors need to be tested at the LH & EZK plugs because they are not easily reached under the hood.

Worf- I don't have JM's CDs, just the factory manual, so I'll try testing the ISV if you could post the procedure, but I think the fact that the idle tries to correct itself means the ISV is working.

This problem is baffling because up until it started the car ran perfectly except for a very slight pinging under full throttle.

I'm getting ready to install new drilled rotors & pads, the Porkensioner & the Bilstein/Eibach combo (scooped on Ebay for $500) and I don't think it's too much to ask for a smooth steady idle!

Thanks for all the input, I will update.

Oh, here are some pics which will explain why I want this to run correctly.