Ed Scherer

At idle, about -61 kPa (0.61 bar or 18 in. Hg of vacuum).

Ed Scherer

This morning, I did another "WD-40 treatment" on the ISV, blowing about 10 seconds worth of spray into a small hose inserted well into the intake hose for the ISV (the one that attaches to the passenger's side Y that's inserted into the MAF rubber boot). It actually seemed to help a little, enough that I figured I'd at least drive to the gas station (I was getting rather low on fuel) a couple of miles away. I discovered that I could pretty much keep the car going if I kept my right foot on the throttle and my left foot on the brake when idling; if I didn't do that (or, alternatively, pop it into neutral), it'd stall. I decided to drive the car to work, and it stalled once while waiting for a light at an intersection (I wasn't fast enough on the throttle).

Generally, the car won't hold idle when I put it in gear; it drops to 500 RPM or so, worse with the A/C on.

Interestingly enough, though, after the latest WD-40 treatment, if I just leave it alone idling (in park), it idles rather smoothly. But then every now and then (maybe every few minutes), it just stops very suddenly without warning. And then restarts just fine.

I don't think I'll drive it again (well, after I get it home again this evening ) until I get this sorted out.

Looks like I'm set up for a loaner LH ECU, which I might be able to get within a couple of days.

Mongo

The fact that there really is no idle control when your accessories are on or when the car is in gear really leads me to believe your ISV is kaput.

John Speake

Vacuum value is a little low, but not a real problem that is affecting the main issue you are chasing.

Ed Scherer

I'm not willing to face reality quite yet; let me try another LH first. If it still doesn't work (and maybe when I'm out of WD-40), then I might just be able to get past my denial phase.

Mongo

Probably the best decision you will ever make is to try another LH.

Ed Scherer

Well, loaner LH from Louie didn't help.

Did another blast of WD-40 at the ISV, too.

Little change in behavior, although it wasn't stalling on me.

I just drove it a little, and I noted that it's just sluggish, too; down on power.

Still idling at about 500 to 550 RPM if the A/C is on and in gear.

I'm wondering if there's anything else I should check out before ripping into the intake, or just turning the car over to someone else to deal with it. I'm getting pretty sick of screwing with it.

rls3335

Hi Ed...

I was just reading your posts on the erregular idle then stall problem and wondered if you figured out the cause. I am having the same problem with my 84' 944. I've got good spark and fuel, speed/references senors have been replaced as well as the fuel pressure regulator. Currently it won't start at all. Any suggestions?

Randal

Jadz928

May have been covered but if not, have you check your idle/WOT switch function? Mainly your idle switch... is it all the way seated where you can hear the micro-switch "click" off throttle?
I had one tightened my throttle cable too much, making it so said switch would not seat. Car exhibited similar stall characteristics to what you've mentioned.

Ed Scherer

Still working on mine; I'm thinking that I have multiple problems, probably all related to aging, failing or leaking stuff in and around the intake.

I don't know how close the 944 is to a 928, but John Speake has a nice "Troubleshooting Porsche 928 Starting Problems" that might apply to some extent to your car.

Yeah, interestingly enough, my TPS doesn't work on the WOT end, but the idle end seems to work OK (at least with engine cold). I've read up some more on the TPS, and it seems like people have also reported problems where the TPS can fail intermittently and somewhat influenced by heat. I'm just going to replace mine.



OK, everyone. I've finally faced reality and am committed to the intake refresh project. Known problems already include vacuum leak and failed TPS, so it's just gotta be done. I've also got a Theo DT999 and a SharkTuner 2 coming so I'll be well armed with everything I need to have a really good before and after data. (I've wanted the diagnostic and tuning tools for quite awhile anyway, not just for myself and future projects, but also to be able to help support our local K.C. area 928 community).

GlenL

The first step to solving a problem is admitting you have one!

I just did that to my local coffee shop owner:

"Is that your 928"

"Yeah"

"I thought it might be after you had the Riviera."

"Yeah, I've got an issue."


Unfortunately a intake refurb ain't going to help me.

Rock on, Ed!

(Didn't read all the posts but you're all over the ISV, I'd expect.)

Ed Scherer

Yeah, the ISV has received about as much attention as it could get via a small hose and sprayed cleaner and lube. It might be working OK; it at least seems to activate properly when tested with a diagnostic tester. Regardless, it will be handing off its duties to a younger, sprier replacement soon.

WallyP

Any relation between A/C compressor and RPM drop?

Mongo

To the guy with the '84 944.

I had one with identical problems. Turned out to be the AFM. Shortly after replacement, the Auxiliary Air Valve went. Check into both. Good luck!

Mongo

Ed, I suppose it's a little late to mention that overspraying the ISV can kill it as well internally.