5.3 Idle problems

[bigbadchev84]

Just recently since it has gotten cold outside 20 degrees and below, our tahoe has been having some problems. I went to start it the other day and it fired up and died immediatley, I fired it up again and the same thing, I can get it started and give it gas and it will run, After about a minute it will idle on its own, But its up and down in rpms.

It has 83k on it and is the new body style, yesterday I changed out what appeared to be oem plugs, wires, fuel filter, and air filter, Cleaned the map sensor, and throttle body.

Right after all this started I figured it was water in the fuel so i dumped a bottle of prestone water remover in a 1/4 tank of gas and some injector cleaner as well.

I fired it up this morning when i got home and it fired right up and stayed running went right up to 1500rpm then down to a slightly rough 1000rpm then back to 1500 for about 5 seconds then back and forth.

Where should i go from here? No check engine light is on

[woodchuck2]

You should put a scan tool on it and check the coolant temp sensor and the ambient air temp sensor, also verify the idle air control is working properly as they do get gumbed up.

[Bo185]

What year is it? And is it DBW?

Might check for intake leaks as well, as the stuff mentioned above.

[brooks294x4]

x2 with the intake leak, take some brake parts cleaner and spray around the intake, it will steady the RPM's out if it hits an airleak in the intake gaskets

[Kwissman]

Pull the vacuum hose off the fuel pressure regulator. If it has gas inside the line the diaphram is bad. The regulator is on the drivers side fuel rail and is about the size of a quarter. This is a common problem that causes it to start and die.

[bigbadchev84]

Sorry It is a 2000 tahoe new body style

[bigbadchev84]

Well I took the air intake off the throttle body and sprayed 1/3 of a can of throttle body cleaner around where the IAC is mounted, fired up and as soon as it cleared out it seems to idle decent, It is warming up now and i will take it out for a test drive soon, will post back up with results.

[Broke_as_a_joke]

intake leak for sure, I see lots of these at work, pretty easy job, couple hours

[D60]

Thread revival. Have '02 5.3 displaying the same symptoms. 180k miles

The only code it's throwing is that it doesn't like how the cat is performing, but of course I can't imagine this would cause problems w cold idle as there's no reason for it to look at O2 when it's ice cold.

I guess I'll go stand in single digits w a can of brakleen or starting fluid and look for intake leaks. Great.

If I can't find anything, what's the next best bet? Just replace ECT?

[Stout Racing]

Sounds like you have a plugged CAT possibly.. do you get a code that says Catalyst effiency below threshold?

ideal would be nice to look at the values on a scan tool look at your ECT Long term fuel trim and your o2 readings and MAP and TPS readings as well

[D60]

Originally Posted by Stout Racing

Sounds like you have a plugged CAT possibly.. do you get a code that says Catalyst effiency below threshold?

Yes.

My symptoms are as the OP describes: upon immediate cold morning startup, idle jumps to 1500, then drops down and almost stalls, then idles lumpy until up to temp.

Once at operating temp truck runs and idles great regardless of ambient temp. At outside temps above, say, 45 degrees, cold idle/startup is also normal w no irregular symptoms.

So we're saying a plugged cat could cause cold idle issues but truck will still run fine once warmed up? I'm having a hard time seeing how.?

I started it up first thing this morning and tried spraying starter fluid all around the base of the intake and at the intake/tb connection. I was unable to produce a change in idle of any sort.

[brooks294x4]

if you have this code, P0420 Catalyst Efficiency Below Threshold your cat is plugged and needs replaced. take your throttle body off, not just the intake tube, and clean it really good. fix those and i bet youll be good to go.