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I have a 2004 ford ranger with a short history of problems...the engine is v6 3.0L OHV.

1) It died 2 summers ago, stopped right in the road, around noon in the middle of July. I live in Tucson so it was pretty hot. The car had been shaking at low rpms for two weeks, and the engine light was off and. I had it towed and the folks replaced the fuel pump module assembly. It was working again.

2) Last summer, it began to shake at low rpms again. The shakes would come in waves, the engine light was on for a few days, then off for a week. I took it to a shop (different than the first) and in their notes they wrote "no active codes, but confirmed customers concern regarding vehicle running rough at idle. Tests determined engine has a misfire due to spark plug wires arking. We removed and replaced plug wires and spark plugs with new. Vehicle appears to be operating as designed." The shaking had indeed stopped.

3) Fast forward to this summer, as soon as the 110 degree days began hitting (3 weeks ago), the truck has been taking 5-10 seconds of cranking before it starts... BUT only during the daytime (sometimes there is a terrible metal-shredding sound during startup, but before it has actually started). Once the temps are below 95 for an hour, the truck starts right up. Then to my delight, the engine light has come back on (2 days ago) along with the rough shakes at low rpms. It used to idle around 1 krpm, and now the truck is very quiet and idling around 1/2 krpm. I got a code reader and the code is p0506 - "idle air control system RPM lower than expected".

So my first thought is, this hot weather just can't be good for the truck. Does anyone have any ideas about this? Is the heat causing all of these problems or is it unrelated that the same/similar symptoms begin showing up like clockwork around the hottest days of summer?

UPDATE: I took the car to a mechanic where they performed a smoke test to detect vacuum leaks. Two leaks were detected, the first was in the air intake hose, and the was coming from the throttle body. The idle air control component looks to be directly connected to the throttle body, hence the p0506 code.

The hose was fixed. They recommended replacing the entire throttle body and then doing another smoke test. For $900 I told them i would replace the throttle body myself... hopefully it won't be too difficult!

  • How many miles on the vehicle? – zipzit Jul 8 '17 at 5:51
  • Its got about 137,100 – Z W Jul 8 '17 at 5:59
  • You probably mean krpm, not rpm; not even big marine diesel engines idle at 1/2 - 1 rpm. As to your question: heat can be a factor in those issues, but usually there is another factor than heat as well. In your case, the other factor could be the amount of miles on the vehicle. Old vehicles just start to fail at some point of time. – juhist Jul 8 '17 at 8:39
  • I did mean krpm - i'll edit for the correction, thanks for spotting! – Z W Jul 8 '17 at 19:18
  • Replacing the throttle body doesn't sound too hard. If the $900 was just labor costs, it sounds high. But then again, the part costs can be quite a lot in the case of throttle bodies. Perhaps ask another question about the throttle body replacement for this particular vehicle? And thanks for confirming that my suspicion was true! – juhist Jul 12 '17 at 20:49
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My immediate idea was that P0506 means there is a vacuum leak somewhere. I googled for P0506, and the first page I found also mentions vacuum leak as the first possible cause of failure: https://www.obd-codes.com/p0506 ...although to be fair, there are some other possible causes as well.

A 13-year old car that has been driven in high temperatures can absolutely have a vacuum leak. Rubber doesn't last forever, and especially in high temperatures, it degrades quicker.

There is already a question about finding vacuum leaks: Finding a possible vacuum leak

If you don't do car repairs yourself, take it to a garage and mention the fault code (P0506) and your suspicion of the cause, a potential vacuum leak.

Do note that both the damaged insulation in the spark plug wire and the vacuum leak have the same underlying cause: rubber parts degrading. So, the failures were to two separate components, but both were caused because of rubber. Do expect similar failures to occur if you continue to drive the car. For example, you can have an oil seal to fail. Or a fuel line can fail and start to drip gasoline.

The temperature differences can mean the rubber slightly expands or contracts due to temperature, and thus can cause the problem to either be present (major vacuum leak) or to not be present (minor vacuum leak).

  • Ahhh i see, thank you for the insight! I absolutely see dry rotted rubber everywhere around Arizona, makes perfect sense that the rubber components in my car would be susceptible too. – Z W Jul 8 '17 at 19:25
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As for the metal shredding sound during startup, I would watch your starter motor. Specifically the overrunning clutch in it, often called a Bendix.

Failures tend to happen more in worn overrunning clutches when they are cold, and frequently a car that will get only partial starter engagement at 0F will work just fine at 20F. It is less common, but a heat-soaked engine compartment can cause the overrunning clutches to not always work correctly.

This is not a common problem (overtemperture failure of the clutch) but it does happen. Generally, rather than changing the clutch (or "Bendix drive") the entire starter motor is changed to repair the issue.

The overrunning clutch is there to protect the starter motor from over speeding when the engine starts turning on it's own, and the starter is still engaged.

  • Very interesting, so are you basically saying that the metal sound is probably not related to the performance issue, except for the fact that both are due to hot temperature outside? – Z W Jul 8 '17 at 19:28
  • That is my take, based upon the information you present, and my experience and knowledge. The latter two are imperfect, so it could be anything. But I would give a careful listen to the starter when you have these conditions. – mongo Jul 9 '17 at 18:46
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did not have a problem with the grinding of metal but the stuttering sound i had a vacuum leak on the drivers side on the bottom side of the pvc hose couldn't see it but felt it with my hand also with misfiring i changed the coil pack cleared it up!! earlier on owning the same truck i had engine shaking and running and misfiring found the problem...was the fuel injection timing unit itself[looks like a distributor] at the back top of engine...upper bushing was wore out ,couldn't tell until i pulled it,bought replacement for $50 at local NAPA ...hope it helps!! i have the same truck but mines 2003

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