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Q: Help with diagnosis - power problem on 2006 Ford E-350

2006 E-350 5.4L First symptom - cruise control would only work intermittently at highway speeds. Seemed to be associated with the brake, as it would work, but if you pushed in brake (slow traffic) and then tried to reinitiate the cruise, it wouldn't work. Over time, cruise worked less and less frequently, until now when it basically doesn't work ever.

Second symptom - about 3 months later (cruise control loss is frustrating, but not a killer... ), every once in a while, the engine would lose power while accelerating while merging into traffic on highway. At least one time the engine light came on. After up to speed, it didn't have problems and engine light would go off. Most times, merging/accellerating wasn't a problem.

Third symptom, and likely unrelated - about 2 weeks before the power issues started, we noticed the AC fan would not blow out the vent while accelerating to merge into traffic. The fan would be blowing, just not coming out the vent. Sometimes you fould feel it blowing out at your feet when this happened.

I took it to a repair shop today, and they said issues 1 & 2 are both the same - the throttle body needs to be replaced. They said the cruise control worked at lower speeds (35-45), but not at highway speeds. I've never used the CC at those lower speeds, so I didn't notice that.

My question - does that make sense? I just don't know enough about the throttle body and it's role to know if it could impact it in those ways.

On item 3, they said the vacuum resevoir was losing vacuum. They also found an unidentified issue in that the AC system pressure was too high, apparently from suspected pluggage. They said they have to pull out parts of the AC to get the vacuum reservoir fixed, so it'd be easy to fix it at the same time, but that they'd have to replace the drier and tubing.

Question - again, does that make sense? What are the risks if I don't fix the AC right now? Does the vacuum system deal with anything more critical than AC vent control? Financially, I don't know that I can get that fixed right now if it's not critical.

Are these common problems in these vans, or is this just one of those things where everything happens at once?

One other thing - he said they tested the battery and it was weak as well. Could that contribute to any of these problems? It seems that the problems are mechanical and not electrical, but I'm not sure. I know my old lumina had a cruise control problem when it had a weak battery.

Thanks for any help you can provide!
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Accutualy a vacume problem can cause all the problems depending on how big a leak it is. The computer uses vacume to sense how much load is being put on the motor and adjust timing and fuel acordingly. Also you are right a battery can cause multipal problems as it maintains a constant voltage, a bad battery can cause computer failier, alternator failier, relay failier and so on. In the desert batteries are the most common cause for other issues.
I little more info after research today. The van has an electric throttle body - no linkage. Would a vacuum leak impact that? I'm not sure how the vacuum system works in modern cars.

I'm getting nervous about several of their diagnosis though. Maybe you can explain it to me. They said that the fuel injectors and the fuel rail were all dirty and needed a good cleaning. While this may be true, how do they know that? When I opened the engine compartments today (the inside cover next to the driver and the hood), it was clear that no one had done much in there. I had to take the air filter cover off to see the throttle body from the front. The case was totally covered in dust, clearly indicating they hadn't opened it. How do you know the throttle body, fuel rail, and injectors are dirty if you don't look? They hadn't pulled the inner cover off the engine compartment either (there were some papers that had fallen back in there a long time ago that were still sitting on it when I opened it). I also checked on one of the parts they quoted and the Ford dealership had it for $100 less than he had it. All that gets me nervous that he's a shister and I can't trust his diagnosis. Thoughts?
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