High idle in Park, difficulty starting at high altitude/cold temperature when warmed up.

[BadaBingM3]

Just in the last few weeks while hunting and camping in Northern Nevada around 6,800 ft elevation and with colder temperatures I noticed my idle would be high in Park when the engine is warmed up and also it took a good 5-7 seconds of turning the engine over and adding little throttle to get it started. Mainly all this when the engine is warmed up. On cold morning starts it started up just fine and idle seemed ok. But once the engine was warmed up after some driving, the idle would be high around 1,200 rpm in park and again, starting the engine seemed like it would not light up unless I gave it a little gas. I'm back home now at lower elevation in Vegas and warmer temperatures and firs start is quick and normal. After about a week back, I noticed today the higher than normal idle in park after the engine was warmed up. I figured it might be a high-altitude and cold temperature problem. But so far now at lower altitude and after the engine is warmed up to running temperature, the idle is once again high in park. So far starting fine. Any ideas? There seems to be no vacuum leaks that trigger a engine check light so far.

RB.

 

[974X4BLACKSPORT]

If you dont have a scanner that can read codes and show live engine data while the engine is running, you should get one, this way you can check all the sensor data that the PCM is getting from the engine, in your case I would look at the ECT (engine coolant temperature) sensor in particular just to make sure it is reading right. Another possibility is that you may have a vacuum leak somewhere causing un-metered air to enter the intake system, this will cause a high idle also. Check all your vacuum hoses and connections for cracks and breaks.

 

[BadaBingM3]

I have a OBDII scanner, I'll have to see how to use it dynamically when the engine is running. Usually I've used to just check codes when presented with one. One thing to add if it helps diagnose. When the idle is running high, if I romp on the throttle and rev the engine a bit, then the idle will drop back to normal rpm's, usually. I'll start checking leaks. By the way, where is the ECT sensor? Near the thermostat I'm guessing? Thank you for the help.

 

[974X4BLACKSPORT]

The ECT sensor for the PCM should be near the thermostat, some engines have one ECT, some have two, (one for gauge, and one for PCM). Another possibility for your high idle, being that "romping" the throttle tends to bring it back down, you could have carbon build up in the throttle body bore interfering and holding the throttle blade open enough to let extra air past. You can check this by looking inside the throttle body (engine off of course), with a flashlight while opening it by hand, look for black soot/carbon build up.

 

[BadaBingM3]

Thanks for all the times!