trying to dianose a fast idle

[joaks]

I posted this here before, thought I fixed it but apparently not so am back with questions.
I get a fast idle probably at least 50% of the time but only when the weather is warm. Maybe 1500 RPM. I can shut off the car and restart and this will usually fix it. I cleaned the MAF with MAF cleaner but the fast idle is still there. My next target was the IACV as this was suggested to me. HOWEVER I found something online where someone had a similar problem (no mention of weather conditions) and it was the TPS. Any way I can rule something out easily?

 

[DinoLover]

Is the throttle body clean?

 

[joaks]

yes, I think.

 

[JHZR2]

Rubber is getting old/hard. Intermittent slight vacuum leak. Shutoff stops the vacuum draw and the rubber resets.

I'd search for pinhole type vac leaks.

Wish I had a fast idle - mine is a bit slow!

 

[mechtech2]

Clean the TB and idle air valve dinner plate clean.
Check and repair all vacuum lines and their connections. Make sure the PCV system is perfect.
All intake connections must be perfect and not leak.

Sound like a lot to do?
I'll betcha cleaning the TB and valve is enough, but go ahead and get it all now for years of trouble free life.

 

[Bgallagher]

Originally Posted By: mechtech2
Clean the TB and idle air valve dinner plate clean.
Check and repair all vacuum lines and their connections. Make sure the PCV system is perfect.
All intake connections must be perfect and not leak.

Sound like a lot to do?
I'll betcha cleaning the TB and valve is enough, but go ahead and get it all now for years of trouble free life.


+1

Do it right the first time and you can forget about it

 

[eljefino]

It depends on subaru's logic.

GM, in my experience, self-calibrates the TPS every time you start the car. So if it sees .35v it says that's "zero" and .36 is not. Restart it, and .36 is the new zero.

For smog reasons, (GM) cars open the idle speed control motor all the way when you're above zero throttle, then when you go to zero, s l o w l y drop back to proper idle RPM. If it sees a TPS reading slightly above zero, it will order a high idle.

There are OBD-II codes for "idle not what the computer wants", a malfunctioning ISC motor or vacuum leak should set said code. If it's garbage in, garbage out from a sensor, there will be no code. Ergo I belive your problem is on the input side of the computer... something like a split hose by the MAF/MAP sensor, coolant sensor out of whack, etc. My first bet is TPS... though this could be misapplied logic, as I've never owned something from Fuji Heavy Industries.

 

[mechtech2]

S dirty or sticky TB will change the idle a little or a lot.
Very inconsistent.