Ramp

This is not the hot start discussion - although maybe similar cause ?

She starts up fine, idles fine and drives fine (relative as I'm still sorting and refreshing). After she's warmed up, if I make a stop, she will start right up and idle fine BUT give it any gas and she stalls unless you feather. Put her back in neutral and she idles fine. Let her sit for a while, issue goes away.

This was happening when I bought the car in December 2018 and I went through some checks and fixes then. Changed the temp 2, changed the fuel filter and checked the tank for sludge. After this, no more problem and I thought I had it licked. Just finished my top end refresh and the issue is back even though everything has been changed out. No lights, no rough idle, no hard start. Just after a drive, if you stop and then restart with a warm engine, she will stall after you put her in gear and give her some gas.

Thoughts ?

Thanks

joejoe

My 86.5 had same symptoms and it was a bad MAF. Supposed to ohm at 380 (new) and mine was 960 or so.

Ramp

Thanks Joejoe. I've read through the MAF threads. While I suppose it could be the MAF, I currently think something else is going on. With a bad MAF, cars usually lose power, are hard to start or idle roughly. I'm not having any of those. Just when you give a warm engine gas, it stalls. Will then start right up and idle perfectly. And, it doesn't always occur.

JayPoorJay

I have an 86 and was having the same problems.

When I looked closer the male to female harness for the tps was (still is) in bad shape. Might double check. In the process of fixing that now.

Also, on closer inspection, their was a small split in a hose that ran up the passenger side plenum. Fixed that... Then more, in changing plugs, one of the hoses (brittle) that ran the length from the oil filler neck, to the main plenum on the drivers side, and to the brake booster, creating vacuum to the brake booster - had sheared off completely at the point of the oil filler (I didn't even see it at the time). I'm sure that there had to be a leak there before... I noticed after experiencing symptoms like you are describing. I am learning that air problems can be big problems... Maybe you missed something during your refresh...? I am new here and to the 928. Mine needs a lot of love. Whenever i work on something, fiddle around in an area, I disturb something creating other issues.

Ramp

Thanks - All vacs new and ok. TPS new, sensors new.

davek9

Don't over look a weak battery, if the battery is low, I recently picked up one of these at this years Autorama in Detroit after having issues with dead battery on my twins-screw.
Main issues was from running all the fans and HVAC blower and short stop and goes.

I can now monitor that charge level in the car when the car is running w/ and w/o various accessories active., it turns red and beeps when reading a Discharge state.
I've noticed a miss fire when the voltage is low (stop and go traffic) idling and it's not loading up, just weak spark i'm thinking.

https://www.batterysaver.com/store/p17/4322.html

Dave K

Ramp

Thanks Dave. Battery is 2yrs and fully charged.

When warm, the stall is more like not getting enough fuel. What sensor could restrict fuel when warm but not cold.

davek9

Temp II to ECU's (cold, uses the warm up map added on to the base map) and the Throttle position switch not telling the ECU's engine is at idle, not cruse changes the mixture.
Need a good O2 sensor too.
Ohm the wires all the way from sensor/switch source to the ECU's harness connectors, else you won't know if its good.
You can test at the ECU connectors and watch for the the change when the throttle is moved off idle, also when Wide open comes in at about 3/4 open, both Idle and WOT go to both ECU's.
Check for good Vacuum at the EZF (affects spark advance).

You'll find it

Dave K

Ramp

Getting back to this. Problem went away until yesterday. Replaced the HVAC relay (unrelated to this of course) and took her for a run. All good. Decided to pull off. let the car heat soak for 5 minutes and then test the AC. Well, car started right up, idles perfect, AC works !, Put her in gear, stalls. Will start easily, and idle fine. Give her gas, stall. Turn off, wait 10 minutes. Start her up, and all is fine. Drive away normally. It seems like vapor lock but not sure if that's possible on 928's.

Dave - Temp2 and TPS are new.

Mrmerlin

I would suggest that you reset the MAF calibration and or have your MAF sent out for testing then recalibrate the MAF to your engine.
NOTE make sure you also have a fresh O2 sensor installed use the factory part here not the generic make if fit part

John Speake

Sounds rather like an intermittent MAF problem. The "not accepting any throttle" sounds like the MAF output may be intermittent.
So going into "limp home" mode.

Try unplugging the MAF connector, check the contacts are clean, then pull back the boot and check for bare wires.

Also suggest you have a look at the LH 35 way connector on the ECU case to check there's no corrosion on the pins.
This can happen if the drain flap on the heater box is blocked.

Jason89s4

I'm gonna go with MrMerlin and John Speake on this one --- an MAF issue or a connector to the MAF, or wiring path to it.
This is based upon your description of perfect start up and idle. But then, when you effectuate the throttle (either by pushing on gas pedal or putting into gear) --and thereby "wake up" the function of the MAF, it acts up.
Had an identical issue (started idled perfectly, but acted up only after you gave it a little gas) and it ended up being one bad pin on the MAF plug.
Jason

Ramp

I will take a look and reinspect the MAF plug - it was cleaned recently with Deoxit as part of the intake refresh. But, if it's a bad connector, then shouldn't it happen randomly rather than only after warm up ?

For more background info, the car only has 42k and was/is in generally good shape, although the years are obvious.

Ramp

Reposting. Since last post in July, the issue never returned - until today. But, contrary to the my thread title, the issue started immediately on a cold start. The car has been sitting for about a week (outside temps about 68). She started right up and settle into a nice idle. Backed out of the driveway, put her in gear, applied gas, stall.

As mentioned, I have replaced all sensors with the intake refresh. I looked at the MAF connector and don't see anything wrong with it, seems to be in good shape (43k miles on car).

What should be next logical step ? Send in the MAF for testing and calibration or change the O2 sensor first ? Do MAF's go out of range with this low mileage ? I cleaned all the connectors and cleaned the wire during the intake refresh. Also, this is an occasional issue as the last time was about 3 months ago and has been running nicely all summer.

dr bob

Did you... relay-relay-relay yet? I found myself stranded at the bottom end of the driveway when low fuel pressure offered the symptoms you describe. Turned out to be caused by a tired fuel pump relay. Swap your good never-used horn relay for the one in the FP relay slot. or use your switched emergency FP relay jumper (30->87) and see if it helps. Test fuel pressure and flow by the WSM methods.

Each fall I threaten to put in a set of the fuel pump spares I have in the parts bin. The last few fall seasons had the car with close to full tank of fuel so it hasn't happened yet. It might this fall. I need to cruise out a bit more than half a tank between now and when the roads get treated with deicer. As luck would have it, there's snow in the weekend forecast. Ground is too warm for it to stay, but it's the reminder that 928 driving season is drawing to a close soon. The Cascades peaks just west of us are white already.