van b

Twice today while I was driving, the engine felt like it shut off while accelerating. It had electrical power, but would not accelerate off idle. No check engine light. Both times I pulled over, shut the key off and restarted and was able to drive away normally.

Has anyone had this happen? What could be the possible causes?

JGEMDOC

do you have semi solid motor mounts? they can throw off timing and cause some bad knock. i had it happen a few times in the past

Petza914

Replace your brake pedal switch - yes, seriously. It's a 996 part number.

yvesvidal

Petza,

Can you elaborate on this? My understanding is that there are two switches: one for triggering the stop lights and one for preparing the cut-off/idling of the engine when it feels brake pressure being applied.

I am also feeling something similar when I run over a bumpy patch of pavement: the engine cuts, goes to idle and I have to accelerate again to relaunch it. I wonder if it is the brake switch or the PSM system detecting an erroneous inputs.

THanks
Yves

Petza914

It's the lower easy to change one that needs to be replaced. It twists into its holder with a 90 degree turn and is a button switch. All cars with drive by wire throttle have a safety feature built into them that cuts off acceleration when the brake pedal is pressed to prevent a runaway vehicle.

You can simulate this if when driving and gently pissing on the accelerator you use your left foot to lightly press the brake pedal.

van b

Any other way than pissing on the accelerator pedal?

But seriously I will give it a try. What is odd is that I have to shut the engine off and restart to get it back going. I searched before posting this and couldn’t find anyone saying they had to shut down and restart, but had seen the brake pedal theory.

Petza914

THat does sound different. With the pedal switch, usually function just returns to normal after a second or two. You might have something else going on. If you have something like a Durametric, I would log live values while you drive for throttle pedal position and throttle plate position. See if when this happens you get weird #s fromnonenor the other.

yvesvidal

Petza914, I found that switch. You can remove it by rotating it 90 degrees as you indicated. That switch control the brake lights and there is a third wire that may be used for engine cut-off, perhaps.
Should I try replacing that switch or place a small and thin shim in between the switch push-rod and the pedal lever, to prevent it from closing too frequently?

Yves

Petza914

Replace it. I've had to do it on both my 997.1 cars.

van b

I connected my Durametric to it the other night and got the attached values with the throttle opening at 0% then 100%. One set for the pedal and another the throttle body.

van b

Drove it to work and back two days this week without incident. Decided to order the brake switch because it was cheap enough to try. Installed it today. Also cleared the two codes when I took the screen shots that I posted.

Keeping my fingers crossed.

van b

Update: I ordered the brake pedal switch and installed it a week ago. All was well with a 200 mile trip last weekend and a couple of drives to work on separate days.

It happened again today with codes p2126 and p2121 which were present the first time this happened. From the research I’ve done, that seems to point to the accelerator pedal, is that correct? Also had a p0638 code.

Any input?

van b

Update: Hopefully this is the last one but I wanted to close this out in the event that it could help others in the future. On the advice of a co worker after researching the codes I ended up ordering a throttle body. Received it and installed it this week. Have put roughly 100-150 miles on without it happening again. Have my fingers crossed.