I have this weird behavior on my car. It began with the rpms going down and up occasionally and sometimes stalling. After some resarch I tought it cloud be the throttle body so I cleaned it and replaced the air filter but it didn't fix it. It has an error in the PCM the code is 443. This is an evap valve failure.

Also took it to the workshop. They told me this code is not the cause of the rpms misbehaving. There they cleaned the MAF and checked the gasoline presure and calibrated the PCM but still the same problem.

At this point I started to realize this weird thing. At speeds like 40Km/h. When I'm slowing down the rpms only misbehave when I don't push the break pedal or push it too little and most likely it will stall. If I push it enough it's like the problem doesn't exist.

Then I took it to a second shop. There they found the alternator was throwing too much voltage. So they repaced it. Now the problem is not that big but still it is stalling. So I think there's a componenet that was burned by the alternator. But the only code it has is 443.

If it were a malfunctioning component should it throw a error code right?

Which systems operate in this scenario? throttle body? transmission? can the evap valve be responsible of this?

Any ideas?


It is either the evap valve, its electrical connector, or the black, rubber vacuum hose that connect the valve to the intake manifold. If it is the vacuum hose, there will likely be rpm fluctuations and stalling, because leaking vacuum affects the air-to-fuel ratio of the engine. Your power brakes rely heavily on the same manifold vacuum, so it sounds like there is definitely a problem in your vacuum hose. It is easy to check yourself and the least expensive to fix.

I had a similar problem with the evap system & valve on my Ford Taurus. In my case, the vacuum hose had become dry and cracked with age. I watched a few YouTube videos to find the location of both ends of the hose. I checked the hose slowly and carefully with my fingers, using a strong flashlight, to find the cracks. I was able to fix the problem with a few dollars worth of new hose purchased from my local auto parts store.

The evap system operates independently of the throttle body and transmission. There is no need to suspect either one.

By the way, there is no such thing as "calibrating" a PCM. It sometimes has to be updated on a new car, but the PCM is really the last thing to ever break on a car.

  • Thanks. Will check it. – loki Jul 16 '20 at 22:01
  • The EGR valve was loose. No more stalling. However it showed check engine light again. Need to see if it is the same. – loki Aug 3 '20 at 21:33

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