Stalling when braking hard.
 

Whenever I have to come to a quick complete stop, she will either completely stall or sputter and stumble around until I give her a little gas. This all started this morning. I can do it whether the transmission is in gear or neutral, but not while at a stand still.
I just changed the plugs and oil. She ran rough on the first couple minutes after the tune up but leveled out after that. She idles around 650 rpms and drives just fine.
This has me stumped.
:irked:

Try changing the fuel filter, its cheap and easy.

first thing that popped into my head was maybe a crack in the vacuum line going to the brake booster that opens up becuase the brake is pressed but idk.

My first thoughts exactly. But she doesn't stall when I pump the brakes or jam on them hard when I'm parked. The rpms don't even budge.

clean the IAC motor and throttle body, it sounds like the IAC motor is not opening fast enough when you jump off the gas and slam on the brakes

It's not just letting off the gas. I came down my street in neutral and stopped quick and she sputtered and almost stalled. I wanted to rule out the transmission.
By quick I don't mean lock the tires up. I mean like getting on them hard but not too hard. You know, enough stoppage to make you shift in your seat.

yeah, well they had a problem with IAC motors causing the engine to stall under braking, im not sure of the exact conditions but they came out with a new iac motor with a dashpot on it to prevent this

Idle Air Control Valve

The idle air control (IAC) valve assembly controls engine idle speed and provides a dashpot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the IAC valve to control the amount of bypassed air. The PCM monitors engine rpm and increases or decreases the IAC duty cycle in order to achieve the desired rpm. The IAC valve [is also] part of the throttle body assembly...

The PCM uses the IAC valve assembly to control:

- No touch start

- Cold engine fast idle for rapid warm-up

- Idle (corrects for engine load)

- Stumble or stalling on deceleration (provides a dashpot function)

- Over-temperature idle boost.


if you have a iac without a dashpot, or an older iac that possibly the dashpot function is not working as it should, this could be your problem

How would I know if this "dash pot" exists?

you caught me with my pants down on that one, i think if you remove it and slide the pintle open with a pocket screwdriver it should move back slowly...if it moves fast then the dashpot is not working...i hope bob or someone can correct me

Ok, I'll try that tomorrow. I've got a lot of work the next 2 weeks. I need to pull my exhaust manifolds and replace the gaskets. I'm buying a right angle drill to drill out the bolts I WILL break.

then don't break them. go get a torch instead and heat them up to a dull red and then slowly work them out. and TAKE YOUR TIME. don't rush getting the bolts out. and buy some never cease or whatever it's called. 6 bucks for like a 12+ oz bottle at autozone.

about the stalling, my mom's ford escort gt has been doing that stalling mess for a long time! it almost always happens by the entrance to her neighborhood, sometimes it'll even stall while turnin IIRC. I'll have to tell her about this for the next time she goes to the shop and see what they say.

No, there's not a chance I will get these out. They have 244K miles of rust, there's not even a bolt hex nut left on a couple of them. Its just a rusty stub. Nothing to grab on to.

How much gas do you have when this happens? If your tank is fairly low, that might be your problem, I know when mine is getting really low, and I stop really fast, (Usually REALLY fast) the truck either just shuts off, or almost shuts off.

If you have a good amount of gas in the tank you should be able to rule this out as a problem however...

Hahaha. I'm gonna smack myself if I find out this is the problem. I'll get some gas tomorrow. I can't get much since I need to fix the filler neck. But I am running lower than a 1/4 tank.
I never had that happen with my other truck. Although now that I think of it, the pump sounds different. Its low and kinda tired. When you turn the keys it's like a groan, more than a whine like my other truck with a "new" pump.

oh...it's one of those situations. haha. sorry bout that man. have fun and good luck. did you get a battery operated drill or corded, hopefully corded

It's going to be corded.
Filling the tank doesn't seem to change it. I'll try the other suggestions tomorrow.

She's idling at 500rpms. Still stalls. I'm going to try a new IAC and run it and see what happens. The IAC on now is original and very cruddy.

Did anyone figure this out? I have a 4.0 Cologne installed a IAC but I haven't checked if it has a dashpot, might be an older IAC... However I did noticed the lower on fuel the more often this happens and like t0x1k said the rpms are not abnormal, it is hard to reproduce for me.

I’m having kind of the same issue truck runs great and brakes fine and all until tonight again was driving home from work and hit the brakes pretty decent to not run a red light but then truck stalled and now won’t start? Last time I replaced the maf and it fixed it but now it just cranks but no start? I’m lost please help! 94 Ford Ranger xlt 4x4 manual 98k miles. Brake booster? Master cylinder?