Rolling idle & periodic overheating

[drewmar74]

All-

Long time non-registered lurker, first time poster.

I've used the search function trying to narrow the cause of this problem down but figured I'd bounce it off y'all and see what y'all think.

I drive a 2000 Sport 4WD V6 SOHC. I am the only owner and got it waaaay back in 1999. It has been a great vehicle but I'm starting to get more and more issues with it..... Here's the latest:

During the early spring I started noticing issues with the truck not wanting to start. Plenty of spark, but it was acting gas starved. It would also hesitate some if I was at speed and needed to accelerate (ex. changing lanes on the interstate). I was beginning to think that it was a fuel pump / fuel pressure / fuel filter issue but it suddenly resolved itself.

Before I could get it into my mechanic, it started a whole different "trick."

Now, it has a rolling idle. My Explorer has always had a low idle (600 rpm) but now its going from the normal 600 up to 1100 rpm or so She also wants to overheat when we're in drive, stopped at a light, and the rolling idle drives the rpms up. There are no odd noises (other than a new harmonic at very low RPM) and the truck does not toss up any "OH CRAP!" lights.... Nothing.

From what I've read, the IAC valve can cause the rolling idle and that make sense. However, does a faulty IAC valve always make noise like some people have described? And why would the high RPM's cause the temp to spike?

Thoughts?

-Abner

 

[wood1]

It is impossible to diagnose a problem efficiently unless you have done a tune up within the last while. Some things that it could be are the IAC, MAF and both can be cleaned. I would certainly look at replacing the fuel and air filters and doing a tune up.

Periodic overheating could be a whole other issue. Ever change the thermostat and examine/service the cooling system?

EDIT:
And forgot to tell you to check for codes.

 

[drewmar74]

Thermostat was replaced back in November. Will climb cooling system this evening and look for anything obvious.

Have already pulled instructions on cleaning IAC, will look for MAF instructions next.

EDIT - wouldn't have some kind of light come on to indicate that there would be codes to pull?

 

[wood1]

May or may not make the light come on. A good mechanic would be able to watch the perimeters while it is running and possible help diagnose a problem real time.

Electric fan or engine driven? Loosing coolant? Did it boil over when it got hot?

 

[drewmar74]

May or may not make the light come on. A good mechanic would be able to watch the perimeters while it is running and possible help diagnose a problem real time.

Electric fan or engine driven? Loosing coolant? Did it boil over when it got hot?

As soon as you get moving again, engine temp drops.

Will also have them check for codes.

 

[wood1]

Fan not working or rad plugged with crap?

 

[RomeovilleIL]

The high engine RPM at idle is caused by the overheating, rather than other way around. The computer is increasing RPM to try to circulate coolant.

Temp rising quickly at a stop is usually a bad thermostat, low coolant levels, weak/failing water pump, or broken fan. The fan is pretty obvious so after ruling that out I would look at the water level in the radiator and the overflow, then squeezing the main radiator hoses with engine running to see if there is fluid and pressure in them (carefull of fan blades). If these check out the thermostat would be next. Remove and test in kitchen in a pot of water. Should be closed when cold. Turn on heat, as water warms up the valve should open. Use a meat thermometer to check temp water when it opens. If doesnt open or takes more than 195 degrees, get a replacement.

 

[drewmar74]

Crawled cooling system last night and topped it off with coolant. She was a smidge low. Changed air filter (she was due anyway) and I'm going to work on cleaning the mass air this week.

All that said, I cleaned the IACV and man, what a difference that made. The idle smoothed out immediately and I haven't been able to replicate the quick spikes in temperature.

If I see any more of those, I'll certainly try the thermostat test and go through the other steps listed.

As an aside, I sincerely appreciate the posts associated with this thread! Sometimes it helps to have someone say "Hey, knucklehead - have you looked at this?" Great stuff and I cannot repay the favor....

 

[wood1]

No problem at all dude. Glad to help out if we can.