Sometimes when i first start my truck if i let it sit there for 2 or 3 mins at an idle it will start running very rough and rich and sometimes the idle gets so low it dies. I can hear it sucking air behind the where the air filter housing goes in the motor. I don't beleive i have an air leak cause this is the only time it does this but im thinking it may be the throttle position sensor or maybe the map sensor. Any ideas?

 

When it does this, try holding the RPMs at around 1500 for 30 seconds or so. If this clears it up and it doesn't come back until you've idled for quite a while, or shut down for a few minutes, it's the front 02 sensor.

 

Thats how it does. If i rev up the rpms it stops then once it idles back down it may or may not do it, but if i drive it then it won't do it again.

 

Yep, time to plug in a new pre-cat oxygen sensor. That's their most common failure mode. Afterward you should get a nicer idle (after the PCM goes closed-loop), better fuel economy, and improved performance, too.

 

Unregistered, are you sure that that fixes it? Because didn't sherriff try that in his and it still did the hiccup at idle? What brand oxygen sensor would you reccomend, bosch or NTK?

 

mine will do the same thing more in the winter tho i want to see how this thread works out.

 

I don't recall Sheriff420's problem, but yeah, low/air sucking idle immediately following transition to closed-loop operation that improves with increased exhaust temperature is an oxygen sensor every darn time. It's not a cure-all on trucks as old as ours that may have other components yearning to return to the Earth from whence they came, but it's a sure bet that when you've got this specific symptom you've got a flaky pre-cat oxygen sensor.

Well, Bosch invented the darn things but I've heard that NTK's are better over the long haul, so I've got a pair of fresh NTK's waiting to go into my truck when I do the 100k maintenance.

 

How many do we have? NKT's site said it has a pre left and pre right and a post cat. i dont remember seeing three last time i was under it. if there is only one in the front do i order left or right? there is a diff in part numbers

 

I believe the only difference between the left and right is the length of their wiring harnesses. Order whichever one has the longest wiring harness. When I changed mine, the first sensor I nabbed from the parts store was an inch too short, and I had to trade it in for the other side. I vaguely recall the left one being longer, but you should call whomever you're ordering it from and ask them to check. I don't completely trust my memory after two years.

 

If the o2 sensor doesn't fix it, it sounds a lot like an IAC problem. I just went through a similar problem on mine. Mine was also idling high though.