one of those idle problems

[swynx]

Replaced the iac. Tps. And ect sensor truck wouldn't start found a o2 sensor that was unpligged for whatever reason got it to start. (Ran till one day then I couldn't get it to start. Already had high idle) starting is taking longer than usual. All these parts helped my high idle but Did nnot solve it. Idles at 2500 till warmed up then at 1500. Haven't tested furl pressure or looked for leaks but when I'm going down hill and engine breaking. It'll start surging like a missfire. Doesn't sound like one tho. And when I turn it off it makes a hissing sound.

Clues to any thing I should replace? I have a new fuel pump just waiting for my new tools to arrive. Still need to buy o2 sensors and a new maf.

Cleaned abunch of gunk from inside the first few inches of the throttlebody. Plan to take it off and clean the holy crap out of it. Its got quite a residue in it

 

[Earl43P]

"when I turn it off it makes a hissing sound"

Look for the vacuum reservoir, should be either a black plastic sphere or torpedo shaped.

Check the line coming out of it, which should go to the firewall for the HVAC Controls.

That line out tends to crack, rendering your heater controls inoperative or sluggish to change vent/floor/Defrost.

That reservoir (and Air Conditioner equalizing Hi/Low pressure after shut-off) should be the only things that can hiss.


A good test for the vacuum accumulator is to run the engine, then shut it off.
As the quiet settles, turn your Vent to floor, then defrost. You should hear the vacuum actuators in the dash make their changes at least two different times. If not, the accumulator's pressure has bled down through the checkvalve at the accumulator and out of that line to the HVAC/firewall. It could also be the line from the engine TO the vacuum reservoir. You might find that accumulator under the air filter, bolted to the fender liner, or mounted atop the heater blower box (usually that is the torpedo shaped one).

That big of a vacuum leak can affect your idle.

 

[RonD]

Yes, that high of an idle would be the sign of a vacuum leak.

A cold engine needs a rich mixture to start and run, too much air leans it out so hard to start.

4.0l is known for getting an air leak in the lower intake manifold gasket, usually re-tightening the bolts will fix it.
If you think leak is in the "vacuum system" then pull and cap each vacuum line from the intake until idle drops.
When you pull off a vacuum line from the intake the idle should go up, or engine will start running rough, if it doesn't then check that line closely it may be your leak, plug that connection and idle should drop.


O2 sensors are not used until engine gets warmed up or exhaust manifolds get to 600+degs, so they can not cause hard starts, just FYI

 

[swynx]

Allright ill have to check those. Would do it today but I replaced a fuel pump in a Camry. I'm pooped. Thank guys

 

[swynx]

I found the leak but still had a high idle. Unplugged the iac idle dropped aand ran rough. Unplugged Tps idle dropped a touch then went up. Unplugged mass air flow with it still attached to the intake ran fine for a few then started loping. Took off the intake tube and unplugged the maf it ran way better. Started right up. Idled great till it realized there was no maf. I think the maf is bad. Wouldn't doubt it. The previous owner ran the truck for who knows how long without a air filter. Pulled the maf unit off and found lots of dirt and chunks of stuff in there. My torch bits don't have the whole in the center so I can't clean it up bit I did blow ssome air in there. Ill replace it on payday