Welcome all 928 forum refugees!
User avatar
By WyattsRide
#13545
I've been experiencing this lately. When the engine is hot (not overheated), slowing to a stop and taking it out of gear. The idle surges ,drops real low and then stalls.I may even hear a low backfire when I get out of gear. It will sometimes start right up and idle. Or if it keeps stalling, I'll have to have the clutch pressed in, start it, put it in gear and go. This does not happen in normal driving times. Even when the engine is up to temp. It seems it takes a lot of driving for it to happen.

Example Saturday. Did some very spirited driving for the first 60 miles. No problems when coming to a stop, parking etc. It sat parked for about 45 mins. On the way home we did some more high speed driving for another 60 miles. But coming into town and having red lights and stops, the stalling and rough idle problems started. I really had to baby it the last 10 miles of starts and stops, until I could drift it into my driveway.

Before yesterday, I removed and tested the ISV that I replaced in 2014. About 12k miles on it. It tested (I think) fine with a 9v battery. Clicking open and close quickly. Sprayed it with a little WD40, even though I'm not sure that trick works on a 85 MY ISV before I put it back in.

What else can I check before driving to Frenzy at the end of Sept?

Note:
ISV is a Bosch
Short harness TPS and MAF was also replaced in 2014

(I posted this same question at RL 928 board)
User avatar
By worf
#13552
What is the history of your mass-air sensor?
User avatar
By worf
#13584
WyattsRide wrote: Mon Aug 31, 2020 1:19 pm Replaced MAF in 2014
With what? From who? New is NLA.
User avatar
By SeanR
#13611
That’s going to be key. I’ve had several failure from one company and zero from another. The first had a habit of being way to lean on the top end.
worf wrote: Mon Aug 31, 2020 2:26 pm
WyattsRide wrote: Mon Aug 31, 2020 1:19 pm Replaced MAF in 2014
With what? From who? New is NLA.
User avatar
By worf
#13612
SeanR wrote: Mon Aug 31, 2020 3:26 pm That’s going to be key. I’ve had several failure from one company and zero from another. The first had a habit of being way to lean on the top end.
I've had failures of rebuilt units from "both" companies.
User avatar
By WyattsRide
#13638
Got the new MAF from Roger. Not sure where he got it from. I sent back the original to him at that time and he sent me the new one (rebuilt?).
User avatar
By worf
#13674
WyattsRide wrote: Mon Aug 31, 2020 4:27 pm Got the new MAF from Roger. Not sure where he got it from. I sent back the original to him at that time and he sent me the new one (rebuilt?).
Anyone nearby that would allow you do borrow their mass-air sensor for a test?

And, I suggest you ohm-out your idle switch at the EZF and LH ECU connectors. (Pin outs are in the LH/EZF troubleshooting guide on the CDs.)

When it dies does it restart easily? Or do you need to crank it a bit?
User avatar
By WyattsRide
#13685
worf wrote: Mon Aug 31, 2020 5:15 pm
WyattsRide wrote: Mon Aug 31, 2020 4:27 pm Got the new MAF from Roger. Not sure where he got it from. I sent back the original to him at that time and he sent me the new one (rebuilt?).
Anyone nearby that would allow you do borrow their mass-air sensor for a test?

And, I suggest you ohm-out your idle switch at the EZF and LH ECU connectors. (Pin outs are in the LH/EZF troubleshooting guide on the CDs.)

When it dies does it restart easily? Or do you need to crank it a bit?
I possibly do. I will have to look into that.

Can you expand on ohm-out the idle switch? I will have to check my CDs for that troubleshooting guide.

It will restart easily. But, it won't stay running. Unless I hold the clutch in and press the gas to keep the revs up. If not, it will die.
User avatar
By worf
#14285
WyattsRide wrote: Wed Sep 02, 2020 9:21 amInvoice says: MAF- Rebuilt - Injection Labs
Injection labs and JDS are the ‘gold standard’ for rebuilt Mass-Air Sensors.

However, I have had “infant mortality” of examples of both firm’s work.

Find someone in your area with an LH 928 (can be any 928 that uses that sensor so ‘84 (Euro) to ‘95.)

If you haven’t found the LH/EZF guide, post back.
User avatar
By Rdon
#14365
Rick, these pictures show the internals of the TPS (S4 version, don’t know about earlier cars). I experienced the problem you describe and traced it to failed solder joints in the TPS. Cold, no problem; after heat soak, stalling and surging idle.

These pics of the internals may help you with electrical testing of your TPS, note that my labeling is correct despite appearing to be “reversed” from the actual switch positions. The micro switch on the left is the idle switch which you can hear to click when operated. The WOT switch is on the right and is silent. You will also note the failed solder joints. With the TPS removed from the car and on the bench it tested normally. However, if i tapped on the case, it would intermittently fail due to the bad solder joints. Seems that when heat soaked, continuity was lost at those bad solders.

You may have indicated that you had installed a new TPS but it costs nothing to check it, right?

I chose to reflow the solder and reuse the TPS and all is well. I’m using the same MAF, that was not the problem in my case (this time!)


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User avatar
By linderpat
#15035
OK, he's got a known good MAF and a known good TPS. Let's keep our fingers crossed.
The thing with the TPS is that you have to align it right on the throttle body - 1 degree open of the plate and you hear the very faint "click". I don't know how you do this with the throttle body on the car. Also, how hard is it to remove the TPS in situ? I did all of my work on the bench when I did my top end refresh. Rick isn't diving that deep unless he has to.
User avatar
By WyattsRide
#15134
I'll be trying Ed's MAF this weekend.

Now the TPS, well we'll see about that. Without removing the Intake Manifold (which I don't want to do right now) I can't see how I can remove the TPS and reinstall a different one. Especially if it critical to get it back in the exact same position. I can remove the "T" to get some access, but I don't think that's enough. Anyone ever try this on a 85 engine?
User avatar
By worf
#15148
WyattsRide wrote: Fri Sep 04, 2020 11:32 am I'll be trying Ed's MAF this weekend.

Now the TPS, well we'll see about that. Without removing the Intake Manifold (which I don't want to do right now) I can't see how I can remove the TPS and reinstall a different one. Especially if it critical to get it back in the exact same position. I can remove the "T" to get some access, but I don't think that's enough. Anyone ever try this on a 85 engine?
Like I wrote above: You test at the ECU.

I’ll post the WSM pages presently.
User avatar
By worf
#15174
ECU Plug Pin Outs:
Attachments
Test Plan EZF and LH 85+_Page_32.jpg
Test Plan EZF and LH 85+_Page_31.jpg
Last edited by worf on Fri Sep 04, 2020 1:20 pm, edited 1 time in total.
User avatar
By worf
#15177
EZF Tests:
Attachments
Test Plan EZF and LH 85+_Page_16.jpg
Test Plan EZF and LH 85+_Page_17.jpg
User avatar
By worf
#15178
LH Tests:
Attachments
Test Plan EZF and LH 85+_Page_23.jpg
User avatar
By WyattsRide
#15184
Thank you WORF. I'll print that out and give it a go.

I can't look at my CD anymore at work because of a new computer with no CD player. I keep forgetting to bring it home.
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