My truck suddently started to high idle at 1100 rpm on park,

So i checked for vacuum leaks, none, I cleaned the throttle body, nothing, I plugged the IAC and the intake openning for the iac tube my truck idled at 500 rpm (is this normal?), could i have a faulty iac valve?

thanx

 

Sure sounds like a vacuum leak. Leaking intake manifold gasket?

 

SHould i spray the ports of the intake with carb cleaner? could my intake elbow have leaks that cause this?

 

When I had a high-idle problem, I ended up rigging up a little smoke 'machine' to find the leak. Can't remember exactly what I did, but there was a coffee can, burning paper and an air compressor involved. Probably duct tape too. Once you start pumping the smoke in, the leak shows up pretty fast.

Carb cleaner/propane will work too, but it's not quite as accurate, and a little scarier.

 

I just cleaned the Iac, no good, and sprayed alot of carb cleaner to recheck for leaks on hoses, nothing, im stuck... I taped the hole on the thorttle plate and rpms droped to 900 which is more drivable i guess... And It makes me suspect the intake elbow... But the fact that with the iac plugged the engine ran at 500 rpm makes me believe its still the iac....
The smoke thing sounds cool, im gonna try it

 

Check the PCV hose for cracks. The elbows get soft over time and crack.

Might help if we knew what you were working on

 

hahaha yeah sorry, on a 2002 f150 5.4, I narrowed it down to either being the pcv tube or the intake gasket. I stopped the air flow through the throttle body, plugged the iac and the engine was still idling at 400 rpms. So it is getting air from somewhere else. I also sprayed carb cleaner to every other hose...

I will try and plug the pcv line to see what happens, but its very difficult to get back there, its just plugged in right? I wont break anything else if i force it out without looking?

 

Ok I checked for vacuum leaks, none...... The pcv valev was bad and letting some air through and was fixed...

So I was messing with the TP sensor, and when i unpugged my idle goes back to perfect! could this be my culprit?
Also theres standard motors, airtex/wells delphi brands, whcihc one will you take?

 

Ok I checked the TPS voltage, the pcm is sending a steady 5 volt signal and 12 v ground.
when the throtle plate is closed the signal cable is reading me 1.3-1.2 volts, which is too high, its supposed to be .98, it moves when i move teh throttle plate up till 4.6, , and it kinda jumps but im not sure if its my hand doing the jumping with the thortle cable. When i let it return it wants to go back to .98 but imidiatly it jumps back to 1.3-.2 volts at closed position.

I read on how to test this on a sticky somewhere, but it never states anything if your closed throttle position has to much voltage.

Is 1.3 too much? And is it the sensors fault?

Nobody has had experience with these?

Thanx

 

Ok changed the TPs, also changed the pcv with the elbows to have peace of mind, nothing... ( I obiously reseted the pcm)..

Still stuck,
any othe ideas?
My gas milliage is really sucking idling at 1000 rpms...

 

I recently changed my fuel pump, could i have excesive fuel preasure or could my regulator be bad? I dont know where else to look

 

Maybe, but I'm guessing the computer would throw an error. Something still bugs me: you plugged the intake and IAC, and it still ran? If that's right, there has got to be a leak somewhere. Really throwing it against the wall to see what sticks here, but could there be a leak in the brake booster big enough to cause fast idle? Usually you can hear those, but maybe try pinching off that vacuum hose. Like I said, throwing ***** against the wall...

 

Yeah there was a perforation made to teh throttle plate, I rpelaced it, and there was a vacuum in the elbow that held the pvc, change it also, now the engine will die when i unplug the iac... the idle has somewhat lowered since the thread started, im in 900 in P, it takes a while to calmn down from any start, and it jumps trying to go to 750 at times... I just ordered a IAC valve but it will take a while to get here, My current iac is not sticking open and i cleaned it, but maybe the spring is too week opening too much the internal valve thing.
Tomorrow or monday im gonna take the whole TB off and clean it again and change every gasket and see.

Its actually irratating me since ive been throwing parts and a lot of fuel at it...

thanx

 

Another thing that could be causing this, could a faulty tstat cause this?

I ordered a motorcraft one along with the IAc..

 

Changed everything, and cleaned everything again, :

New: pcv hose and valve
tps
tstat
IAC
EGR
Some Vacuum lines.

My idle went down, but now it jumps constantly between 850 and 750 and i have a humming sound comming from the intake filter assembly...

Could my new IAC be bad?