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I knew I shouldn't have said anything. Today, it came back. So I guess I can rule out the MAF. Took a drive around town running errands - all good and with a newly sorted ice cold AC. After last errand, started right up, perfect idle, put it in gear, give it gas, stall. I drove it a few minutes feathering the gas. Then pulled over. Turned all off. Waited 2 minutes, maybe less Started the car, drove away, no issue all the way home.
The only sensor I did not change was the air temp sensor in the airbox. Can this be related ? I have the faster sensor but haven't gotten around to installing it.
I wondered a while back about vapor lock - but IIRC, it's happened in cooler weather and possibly when the engine was cold - although the vast majority always after the engine as been warmed up, but not necessarily hot.
Rereading this thread from the beginning, lots of MAF discussion but not much on the supporting systems. I suffered some similar erratic symptoms a while ago now that turned out to be related to fuel pressure. The pump wasn't getting full current thanks to a failing fuel pump relay, and it was intermittent. -Almost- always started and ran perfectly, until it didn't. Checked fuel pressure with a jumper in the relay socket, and for grins I decided to try and start it. First thing I checked. Solution found: replace the relay.
Intermittent issues too often cause us to jump to expensive and complex diagnoses and attempts at fixes. Before you dive down into that abyss, do the simple cheap stuff to rule things out. Repeating ad mausoleum the Jim Bailey "relay-relay-relay" mantra is always appropriate for situations like this. "Clean and tighten the positive battery terminal connections" is always a good idea even if you don't have any problems yet. Operative word: yet. Original battery ground strap? Get a new tinned marine-quality upgrade strap. Have you cleaned ALL the ground points on the car in the last year or maybe two? Annual electrical maintenance protocol procedure, than you. Battery fully charged and healthy? Solution is self-explanatory.
Sensor connections get tired a lot more often than the sensors themselves fail. Sometimes a new sensor will seem to fix a symptom, mostly because the connections were cleaned or they cleaned themselves when removed and replaced. Clean the connections, inspect and replace connectors as needed. Then a new sensor if cleaning didn't solve the symptom.
Wiring is getting old and tired. Got cracked insulation and/or corrosion back into the wire insulation? Repair or replace. Most sensors, including the MAF, temp sensors, and switches that connect to smart controllers, all tend to operate at pretty low current draws. A small amount of resistance in connectors and wiring can mess with the reading the controller sees, even when the sensor itself is still working. Don't be afraid to spend on new wiring when your old original stuff is falling apart.
Got varmints or vermin? Mice love to eat rubber and plastic stuff. Keep Mice Out Of Your Car. Use ultrasonic repellers, set traps, Store Your Car Up High, mothballs in the engine bay, as needed to keep from suffering damage from rodents. I was working on a neighbor's MB, replacing fuel pumps, so had the car out in the driveway for a few days while parts shipped (from Roger...). Finished, owner started the car, two of the cutest grey mice leapt from the front wheel area and scampered into the bushes. No damage is obvious, at least not yet.
Rereading this thread from the beginning, lots of MAF discussion but not much on the supporting systems. I suffered some similar erratic symptoms a while ago now that turned out to be related to fuel pressure. The pump wasn't getting full current thanks to a failing fuel pump relay, and it was intermittent. -Almost- always started and ran perfectly, until it didn't. Checked fuel pressure with a jumper in the relay socket, and for grins I decided to try and start it. First thing I checked. Solution found: replace the relay.
Intermittent issues too often cause us to jump to expensive and complex diagnoses and attempts at fixes. Before you dive down into that abyss, do the simple cheap stuff to rule things out. Repeating ad mausoleum the Jim Bailey "relay-relay-relay" mantra is always appropriate for situations like this.
Having repeated the mantra >1K times you would think I would have done this. Tomorrow!
"Clean and tighten the positive battery terminal connections" is always a good idea even if you don't have any problems yet. Operative word: yet. Original battery ground strap? Get a new tinned marine-quality upgrade strap. Have you cleaned ALL the ground points on the car in the last year or maybe two? Annual electrical maintenance protocol procedure, than you. Battery fully charged and healthy? Solution is self-explanatory.
All done.
Sensor connections get tired a lot more often than the sensors themselves fail. Sometimes a new sensor will seem to fix a symptom, mostly because the connections were cleaned or they cleaned themselves when removed and replaced. Clean the connections, inspect and replace connectors as needed. Then a new sensor if cleaning didn't solve the symptom.
Wiring is getting old and tired. Got cracked insulation and/or corrosion back into the wire insulation? Repair or replace. Most sensors, including the MAF, temp sensors, and switches that connect to smart controllers, all tend to operate at pretty low current draws. A small amount of resistance in connectors and wiring can mess with the reading the controller sees, even when the sensor itself is still working. Don't be afraid to spend on new wiring when your old original stuff is falling apart.
Again, good advice, and I am at the beginning of that process.
Got varmints or vermin? Mice love to eat rubber and plastic stuff. Keep Mice Out Of Your Car. Use ultrasonic repellers, set traps, Store Your Car Up High, mothballs in the engine bay, as needed to keep from suffering damage from rodents. I was working on a neighbor's MB, replacing fuel pumps, so had the car out in the driveway for a few days while parts shipped (from Roger...). Finished, owner started the car, two of the cutest grey mice leapt from the front wheel area and scampered into the bushes. No damage is obvious, at least not yet.
2 big mean outside farm hunting cats. Screw the vermin!
Back to reading...
Thanks dr bob, sometimes it's good to get a little refocused, one of the things this forum is very good at providing.
Bumping this thread because I have a similar issue. Ramp, did you ever figure out the problem?
Unfortunately not but the issue has become less often for some reason. While all my relays were cleaned, I did not replace the fuel pump relay. Rather than do so, I'm going to carry a spare and next time it happens replace the relay and see if that has any effect. I believe it's XX and is a standard #57 - correct ?
It is indeed at position XX in your 1986 car. It is a standard 53b relay. Get a good one.
Tangent...
At least a decade or so ago now, I arranged for a spare rebuilt LHA box. Rich Andrade did the work, and recommended that I just install the rebuilt one and keep the old one as the spare. Stubborn Bob... The Good News part of this is that the original finally failed while I was at home, so I happened to be where the car and the spare controller happened to be, and also by the tools needed to do the exchange. As I went through that what-if mental exercise, I though about how inconvenient it is to have to do roadside repairs, and how especially annoying it would have been if I'd needed to describe to mrs dr bob exactly where the part was stored, and ask her to drive the part to wherever I happened to be. I also remember Marc Thomas (of Devek fame) making a midnight run across the state to bring a controller to a traveler coming late from Arizona for a Devek Days event in the bay area. I can't depend on that kind of support; I'm more attuned to giving it rather than receiving it if I can. The outcome of that whole episode is that I go ahead and replace suspect pieces with new as soon as they are suspect. I might restock the old bits as spares, but only after I can verify that they are truly serviceable pieces. I still carry a spare 53b relay in the car, but have already replaced the Big 4 with new, plus there's a switched jumper and relay removal tools secured behind the tool panel. Just having that stuff means I won't ever need them, if Carma means anything.
Lesson for you if you want it: Buy half a dozen top-quality 53b relays now, install four of them and carry the other two. Then look for recurring symptoms, knowing that they won't be caused by failing relays. Much Easier to swap them in the comfort and safety of your own workspace, vs. on the side of a lonely road in inclement weather. With mrs ramp encouraging you as she stands out in the inclement weather while you are butt-up where her feet should be.
Still not sure/understanding why a low setting would cause the stalling only very intermittently and then go away. In any event, knowing the setting is low, seems like a good idea to adjust. Went relatively smoothly. I drilled about 1/8" into the cap (not through) and then used a screw extractor and the cap spun right off. The POT adjustment is very very light to the touch, hardly any resistance turning. Here are some pics for future reference.
The POT adjustment is very very sensitive and there is almost no resistance turning I didn't drill all the way through the cap so I can reuse it. Before adjustment After Adjustment
reviving this post a bit with a new twist. I have been executing an intake refresh on my 87. As part of that I have been checking the throttle body/maf assembly for leaks. I have the maf assembled on the throttle body with the throttle body mounted to the intake, but with the tb air outlets sealed with subber gaskets I made, and have the maf capped with a 3" rubber cap. This way I can pressurize maf, tb, isv and hoses before intalling on the car. When I apply pressure through the system I have found that my co pot does not have the cap, and that a surprising amount of air is coming from the pot adjuster. Technically this leak is pre throttle plate, and I don't think the leak is air measured by the maf, so maybe this is ok? To me after seeing the above picture of the cap it seems porsche designed the cap with an oring to seal this leak. But it seems like most mafs that have been rebuilt don't have the cap? Is that true? Mine was rebuilt by injection labs by the po and doesn't have a cap, anyone have any input on if the sealed cap is necessary?
Last edited by Popoboy944; 04-22-2022 at 01:13 PM.
Surprised to hear air is getting in there...wonder how, I don't recall seeing passage into that part of the MAF. A lot of folks use the adjuster and I think they leave the pot uncovered. I got a rebuilt one from JDS and pot did not have a cover on it.
Surprised to hear air is getting in there...wonder how, I don't recall seeing passage into that part of the MAF. A lot of folks use the adjuster and I think they leave the pot uncovered. I got a rebuilt one from JDS and pot did not have a cover on it.
it's blowing past the thread of the adjuster. I don't know what is inside of it further up from the adjuster and if there is something that should be sealing there or not.
There isn't a thread on the adjuster. It just turns a potentiometer on the circuit board. It's an electronic adjuster, not an air adjuster.
There is a flexible 'O' ring on the adjuster shaft but they can shrink with age and heat.. I would think the leakage past it is insignificant as it is just measured as part of the total air. It's before the throttle plate
There isn't a thread on the adjuster. It just turns a potentiometer on the circuit board. It's an electronic adjuster, not an air adjuster.
There is a flexible 'O' ring on the adjuster shaft but they can shrink with age and heat.. I would think the leakage past it is insignificant as it is just measured as part of the total air. It's before the throttle plate
thanks a lot John, I really didn't know what was inside. This helps. Im guessing there is no easy way then to replace that oring without reopening/ungluing the cover? Good to hear also that it probably doesn't matter. Thought so but figured I should check with the brain trust to be sure!
06-27-2020, 03:33 PM
