jgrosjean

My feeling is that it is the air flow sensor sticking or something to do with the way the computer interprets the signal. My car runs perfectly except for this down-hill condition occurring sometimes. If you press the gas pedal, it go back to normal. I know the tank and filter are clean because i had it out to work in the heater unit. From the comments above, it seems to be a characteristic of this engine. If you have the cruise control on, this will sometimes cause it to become unstable at the bottom of a long hill.

psiegel

My feeling is that there must be some negative pressure that builds up within the AMF causing the "barn door" to stay shut. When I had an AMF it was even more of a problem at high altitudes (9,700') due to a greater pressure differential. Again, just a guess.
Peter

Richard Curtis

Oddly enough, when I had the issue, it always occurred at the same place on a highway near my house. Always going downhill in fifth gear at a steady speed around 55 mph. I haven't had the issue for several years now, and I've not touched the air-flow meter.

Ravioliv

Hi all,
Digging out this very old post as I am battle with same symptoms but outside the AFM , I could not figure out in this post if all the guys having reported it fixed it that way...?
In my case I am running a MAF Kit AND I have tried a different MAF sensor without success...

Now ordered an O2 sensor and idle switch as these were mentioned to play a role but I still do not get the rational with the O2 Sensor ( coasting downhill = no fuel injection ....) but as it is original on my car...
The idle switch I have tested OK with the multimeter so unless failing intermittently I do not believe it

Will post the results but was wondering if someone remembering the issue could post some confirmed fix

Cheers!

Earlydays

I had the same problem...occasionally losing power while going down hill....it went away after I replaced the DME relay.

joerg65

I too had this same issue and thought I’d fixed it when I took apart my AFM and gave it a good clean (ie contacts and arm) but unfortunately I’ve had it a few times since.
My car’s got new a new O2 sensor, DME relay, cleaned fuel tank, new fuel pressure regulator and the only suspect I can think of that’s left is the ECU. Like others have commented, I had assumed the AFM was responsible for this but if you still have it with a MAF maybe it is something funky the ECU does when coasting with minimal/no throttle. I’ve just learned to live with it … but it is disconcerting when you seem to lose power for a second or two.

cjoenck

This is a stretch but hey, is it possible you have a marginal ground strap somewhere? When you run downhill, something shifts ever so slightly. That would be enough to break contact for a few seconds. I know it's far fetched but you all seem to have looked at everything else.

joerg65

A very good thought but I’ve already been there and checked.
One of the uncanny things about this power loss is that it usually occurs on the same part of the same stretch of road - others have made similar comments. It would be interesting to know if anyone with an after market ECU has had this issue

Ravioliv

Well then seems like my new O2 sensor is probably not going to help….
I ordered as well the idle micro switch just in case…despite I have checked the function with a multi meter….maybe when hot who knows…

DME relay , I struggle to see the relation, this could be in random conditions but not in specific conditions like here…
Same for the ECU…unless it is down to the atmospheric pressure ( downhill = altitude…) and that it would be inside the ECU as on my car I could not locate a specific barometric pressure sensor that is sometimes mentioned on our cars…
but amazing that on 30y old cars and so many guys having the issue it has not been found!

No_snivelling

Are there any powerful sources of EMF on that stretch of road? Transformers, Substations, Transmitter towers or power generating stations for instance?

Ravioliv

In my case it happens at different location so I would rule out the EMC factor.
seems more correlated with altitude in fact…

A8KED

There was another post about this issue on 6/24/20 titled "problem when going downhill". There was some speculation as to the cause but no solution. My car has done this for the 10 years I've owned it and continues to do so. I'd love to know the cause and fix.

No_snivelling

That is so strange. If it is altitude related, consider this:

Let's say the problem always occurs as you descend through an altitude of 1,000 feet above sea level. Surely you had to pass that same altitude on your way up, and yet no problems when going up. So if it is altitude then it must be a combination of altitude and nose angle. Positive nose angle on way up, and negative on the way down. Any pilots of ICE aircraft here? LOL.

Or perhaps it has to do with a vacuum or pressure leak that changes with altitude? Or fuel starvation because crud rolling around in the bottom of your tank blocks off the filter? Or fuel tank vent is plugged?
Sorry, just brainstorming here. It is an interesting problem.

Ravioliv

Tank was totally checked last winter (
for this reason and also because the fuel level has dropped inside due to age.
tank cleaned for any debris + new mesh….

also replaced the fuel canister valve that was dead open and logically was applying vaccuum to the tank when coasting down with no throttle…so was almost sure this was the cause as tank even started to deform due tu the vaccum!
but even with new valve ( or even disconnecting the valve completely to isolate the tank from intake ) it still does it….

Still fuel pump not replaced because I did not have part at the time of tank rebuild, but this was a mistake as now I have the pump but don t like the idea of getting the content of the tank pouring over me when doing the change…but as no fuel cut in any other situation I doubt it is the pump…
will post result as soon as O2 sensor is replaced and I could I drive enough to test…

Ravioliv

Hello guys,
Took some time to perform some winter jobs on the car and be able to update the situation.
Fuel pump was replaced preventively.
O2 Sensor was replaced because I suspected this could be the cause of rough cold start, high fuel consumption and misfire when decelerating .
I only had the chance to make a short confirmation drive ( we had several weeks with presence of snow and wet / salty roads here in Switzerland )

Rough cold start and misfire seems to have gone which I attribute to the O2 sensor.
The power loss in downhills, I did not have neither, but it used to happen not around my neighborhood but more on longer journey with a bit of mountain roads which I should have opportunity to test in 2 weeks when going to a track event, so hopefully will be able to provide a more complete feedback....
Fingers crossed...