I need some help. I have a 1999 Ram 1500 with a 5.2. When I start the truck it will idle for a while fine for a few minutes, then it will start to idle real rough and it has a loud (what seems) to be a vacuum sound coming from the TB. Sounds like a terrible vacuum leak. The truck does not stall. Once I press on the accelerator it will go away and be ok.

If I am driving it I have to floor the truck in order to clear it up.


It can happen multiple time thought out the day. Cold hot doesn’t matter.
Has anyone experienced this and if so have any clue. MAP sensor?

 

Service engine lite on?

How many miles on your truck?

Have you checked the plenum?

Welcome to DF!

 

I had the same problem, both of my 02 sensors were crapped up but i had no CEL come on.

 

I have the same problem right now. Going to get an o2 sensor this weekend and see what happens.

 

The symptom is perfectly consistent with the end of life behavior of an oxygen sensor. A cold oxygen sensor reads (incorrectly) rich, which is the main reason we have an open loop mode (and heated O2 sensors) in the first place. At end of service life, the sensor requires more heat to function (almost) normally. When you crank up the RPMs to clear the problem, you're sending more hot exhaust gas flying down the pipe, heating the sensor.

Way back when oxygen sensors were brand new automotive technology most cars turned on the CEL at 60,000 miles to compel their owners to take them in for servicing and a new O2 sensor. I hated it at the time, but since they removed that feature I've begun to think that it was actually a good idea.

We seem to be having a rush of failed O2 sensors lately.

 

Same problem here, and I wonder if both should be replaced or just one of them?

 

Just do the pre-cat if you're okay with waiting around for the post-cat to puke and throw you a code. The pre-cat sensor value is used to set mixture and timing, while the post-cat is there only to detect a failed catalytic converter and doesn't affect engine operation at all.

I usually replace them both at the same time because seeing the CEL come on when I'm hundreds of miles from home and out in the middle of nowhere bothers the heck out of me. It's just a foible I've got -- I don't like squeaks, rattles, wind noise, filthy windshields or nuisance CEL's.

 

Truck has over 200 K miles and yes the CEL is on. Seems that the 02 Pre cat sensor is the culprit based on the replies in this thread.

 

Thanks guys, I had the exact same symptoms and changed the pre-cat O2 sensor yesterday and now the truck runs perfect. Mine was popping back through the intake and would only run right at full throttle. Again thanks, after weeks of trying to figure this out, you pointed me in the right direction. Sweet.

 

Excellent! Glad to hear it!

If this long run of failed oxygen sensors keeps up I'm going to buy some shares of Bosch.