Passport with erratic problems

Hello,

1st timer!!

I am having trouble diagnosting a problem with my 1999 Passport.
When I am on the highway going 65 for a while (1+ hours) and need to stop quickly (ie, traffic backups) the engine revs way down and dies some times, other times it just revs low erratically. It starts up right away but may rev'd down and die again. I have replaced the manifold gaskets last year and just recently replaced two oxygen sensors which were giving an odd reading on the computer at my friends shop. The odd revving stablizes after driving at lower speeds after a while. But it sure make me nervous, especially if the family is in the truck. Any ideas on why this is happening?? Could this have any thing to do with the Airmass meter or Throttle position sensor??

maybe the trottlebody butterfly is carboned up?

Or the intake manifold is bad of not torqued right?

This sounds like another bad intake manifold gasket, which will also cause oxygen sensors to give 'odd readings'. Dont change an oxygen sensor unless you are getting a slow or no activity code, or a heater malfunction code. Other O2 codes mean something else is going on! Do you have a check engine light?
G/luck
Joel

maybe the trottlebody butterfly is carboned up?

Or the intake manifold is bad of not torqued right?

What is the Throttlebody butterfly?? and where is it??

This sounds like another bad intake manifold gasket, which will also cause oxygen sensors to give 'odd readings'. Dont change an oxygen sensor unless you are getting a slow or no activity code, or a heater malfunction code. Other O2 codes mean something else is going on! Do you have a check engine light?
G/luck
Joel

Joel,

Thanks for the tip. No check engine light. If I had a bad gasket wouldn't problem show up all the time, as it did before I had the gasket replaced??Other problem I noticed is when I start the truck. It sometimes revs very high and takes a few minutes to settle down to normal idle revving.

Joel,

Thanks for the tip. No check engine light. If I had a bad gasket wouldn't problem show up all the time, as it did before I had the gasket replaced??Other problem I noticed is when I start the truck. It sometimes revs very high and takes a few minutes to settle down to normal idle revving.

The bad IMG induced problems often go away once the engine warms. Everything expands slighly when warm and can 'seal' off the leaks.
G/luck
Joel

when my intake manifold gasket went bad it took a few months for the CEL to come on. That's when I finally got it fixed, but I knew it was bad already.

Marc