My dads 00' 5.2 5 speed has a idle problem that comes and goes hot or cold. The air cleaner will also become very loud like it is pulling massive amounts of air. Then out of no where it will pick up and idle good and the noise goes away. The plenum has been repaired and the Iac and TPS hane been replaced. Any ideas? The truck has about 130k on it.

 

has it had a tune up lately?

 

could also be a vacuum leak

 

air cleaner gasket?

 

Check the following:

Coolant temp sensor

AIT sensor

O2 Sensors

All three of those will affect the A/F mixture and when it runs rich, it will need way more air. After 3 minutes, the truck goes into closed loop mode and, at that point, the sensors help to lean out the mix making it idle as it's supposed to.

What can happen is when one or more of those components go bad or, intermittent, it goes into open loop mode and, will do so at any time so, check all those components and sensors and verify that they are working correctly.

If you can't or don't have the tools to do so, have a shop run a scan. If they are bad, it will show on the scan tool.

 

whats you exhaust like? i know that when i have the stock muffler on its idled at about 600 RPMS, i cut it out and straight piped it, now it runs at 400RPMS. Maybe this along with the o2sensor could be doing it?

 

The tune up has been in the last 6 mos. Gaskets are good and there are no external vac leaks we could find with the can of carb cleaner sprayed around various points on the engine. We'll try the scan. May be a while for the update cause he's going on a trip. Thanks guys.

 

first things first, its a 2000, which means its obd2, which means there should be a code, if an 02 sensor goes out. or is unplugged, and if theres a code, theres a check engine light. take it to advnace or auto zone, and they can scan it for you free. but it only works if the check enigne lights is on.

 

Check that the IAC has not come loose from the TB.

Make sure that the filter housing is firmly in place on the TB and secured (I have seen these replaced "properly", actually at an angle with a gap to the rear ... easy to do and WRONG).

 

If this occurs shortly after starting up, its probable on o2 thats not heating up fast enough, truck goes into closed loop before o2 is cycling. This happened to mine, was intermittent and went on for years before I found it. Hissing noise is IAC cranking open, also random miss fires, timing goes nuts ect. New brand name O2 sensors did not fix it on mine, only after putting in NTK o2 did they heat up fast enough. Could see this happen with a scanner.