It looks like my 05 GT has decided to develop it's first "real" issue.

It all started about three weeks ago. A few times, right after I started the car and right when the rpm was dropping from the "very high cat idle" back down to the "cold high idle" mode, the rpm would just drop right through the bottom and the engine would die. Needless to say, it started right up every single time.

After the third time it did this, I picked up a can of throttle body cleaner and yanked the TB to clean it. My theory was that the TB was dirty and it was sticking closed for a second when the ECU closed the blade to drop the idle down, so it couldn't open it quickly enough to stabilize the idle, so it died.

The TB was fairly dirty and it did need a good cleaning. After putting it all back together, I THOUGHT that had fixed the problem as it went four days with no issues, EXCEPT the idle speed was generally higher than it should be and it took a very long time to settle down to the normal 750 rpm idle (say at stop lights) even when the engine was hot. I assumed the ECU would have to relearn how to control the idle speed because all the crap around the throttle blades was gone, allowing more air into the engine as low blade angles than before I cleaned it.

Well, yesterday, it decided to add something new to the mix: it died on me while driving down the highway. At the time, I was decelerating, so the engine had little to no throttle. She just died. It was like I turned the key off. The engine was still turning at the 1500 rpm or so, just no spark, no fuel.

The car restarted right away like nothing had happened. But she did it one more time on the way home. Started right back up again as well... Today, she did the exact same thing. And again, she started right back up.

Here is my theory: The crank trigger is going bad. How many pulses does the ECU have to miss before it assumes the engine has stopped and goes into engine halt mode? I don't THINK the cam sensor could be causing this as it is normally used as a sync pulse and is not actually needed once the crank sensor has been synced during start up. The problem SEEMS to happen more often at low throttle settings than at high throttle settings, so I don't think the problem is fuel related.

I just checked and there are no stored codes, which reinforces my opinion that it is the crank trigger. The ECU won't store a trouble code if it thinks the engine just stopped. It's not smart enough to realize that the engine shouldn't just stop while cruising down the road!

So, has anyone else had something like this happen to them? Root cause? Anyone have any other idea what could be causing this problem?

I HATE intermittent problems!!!!

 

Sounds like the TPS is going bad.

 

yeah i would agree....it definately
sounds throttle body related.

either the sensor is flaking out,
or something with the TB itself

 

I disagree with the TB idea, like RRRoamer said, if it was the TB causing the problem, there would likely be a code thrown. Especially after this happening several times in a row, a code would be thrown for sure. If it was the Crank Position sensor like suggested, it makes sense to me that the engine would not throw any codes. I agree with RRRoamer on this one.

 

I have seen 2 of these do the same, Its sounds like a throttle postion sensor going bad.

 

But wouldn't that cause it to throw a code?

 

A crank trigger seems like a good thing to check, but I would trace the wiring from it as much as possible first, before replacing the sensor. I have seen wires that loose connection with good looking insulation on the outside (they were bad from the wire factory). After checking the signal wire continuity as much as you can reach with an ohm meter, then check the connectors to the sensor as best you can (check for pins and sockets that weren't seated).
Also, if you haven't replace your fuel filter, I have also seen plugged fuel filters cause really strange behavior.
Finally, without error codes, you might have a fried computer.
Good luck.

 

Thanks for the insight gents. Right now, I'm on the TPS or crank trigger fence. I replaced the fuel filter about two months ago (with a Motorcraft filter), so I don't think that is the problem.

I guess it is time to open up the service manual and do a little bit of digging!

 

Hell dude, I'd take it into the dealer and let them sort it out. Especially if yer still under warranty.

 

Nope. For two reasons: 1) it is about 4k miles out of warranty and 2) I have YET to see a dealer actually FIX an intermittent problem with anything less than 20 "tries".

If the failing part/connection/wire/etc. would just DIE, then I could track it down and be done with it.

It died again today. This time, I was accelerating slowly (in traffic leaving a stop light) and at about 20 mph, the engine just up and quit. Started right back up like nothing had happened...

 

Have you had the water near the ECU problem? It does somewhat sound like perhaps intermittent wiring/connections on the ECU possibly causing intermittent signal outages. Check there for corrosion?

 

That is for the SJB and it has nothing to do wiht engine function. the ECM for the engine is under the hood.

 

No water. New Mexico is a pretty dry state and we haven't had any rain in a while. Plus, the car is always garaged both at home and at work, so it doesn't ever get much soaking when it does rain.

I think I am going to track down the crank trigger connections and take them off and see how they look. If there is a bit of corrosion on the connectors, removing and replacing them will help to clean them up.

 

I'm not 100% sure how this would work, but I am starting to suspect bad gas. The dying and idle problems all went away the same day I refueled the car. I still had not done any diagnostic work (nothing taken apart, nothing cleaned, nothing...), so that can't explain it.

When I started thinking back on when the problem started, it was right after I refueled it the last time. I always use the same station (Chevron) and I have had nothing but good luck with them in the past, so I wouldn't THINK they would have bad gas, but I sure can't explain how this all started than just stopped on it's own.

I guess time will tell...

 

It just keeps getting stranger and stranger....

 

It's possible that you got a tank of bad gas, it could happen anywhere at just about any time.

One other thing, do they use a different formula of gas around your area in the winter? I've seen it where it would be unusually warm and everyone still has winter gas in their vehicles, so it causes a lot of stalling and no-start problems. It happened around here about 3 or 4 years ago, was 50+ degrees in Feb or March, still using winter gas.

 

We do use winter gas (alcohol) here in the winter. I can't remember the from x to y dates, but it would be around the middle of March. We have been up in the 70s the last few weeks. Maybe...

I REALLY like this explanation MUCH better than "something is dying on my car and I can't figure out what the problem is!!!"

 

Take it to a shady neighborhood and park it with its windows down. In a few minutes, your insurance will help you fix the problem by replacing the faulty component...and the whole car...

 

Ahhhhh,,,, Thanks for the suggestion Arrow. But I think I like the "refill the gas tank and the problem completely goes away" method instead! I haven't had one single issue since I refilled the thing on the 23rd.

 

Wow...what the deuce did they put in yer previous tank?

....You didn't accidentally fill it with diesel, did you? :P