I have read through the idle problem threads and can't seem to find anything that approximates the behavior I am seeing, I was hoping someone could give me some direction narrowing the possible root causes and point me at a primary system to start troubleshooting.

My SE has been running fine no problems, just over 100K on a well kept car, plugs and wires are relatively new (1000 miles maybe). The car sat for 6 weeks or so and I started it up and moved it to the other side of the house, it ran fine. The next time I started it it idled really really rough and would stall without a little bit of foot on the gas.

The interesting thing is as long as I give it enough gas to keep the rpm's between 1000 and 3500 or 4000, I can drive the car and it seems like it is running fine. If I sit in neutral and give it enough gas to raise the idle at a slow rate, the idle will raise to 4k or so, then it seems to choke and the idle drops down below 1000 to the point of stall, then catches again, raises up to 4k, chokes back down, up, down, up, down. It will keep doing that as long as I sit there giving it some steady gas. After a few minutes I seemed to get a little smoke from underneath.

My first thought was maybe I blew the cat internals back into the muffler and blocked it (or mice built a nest in the exhaust). It's a relatively new racing beat muffler and Bonez Highflow cat, with a new mid pipe (maybe 2k miles on the setup). But I guess if I had a clogged exhaust I would expect the car to run bad at all RPM levels. And at mid RPMs it doesnt "sound" clogged.

Anyone ever see this or have some thoughts as to whether I should start by looking for a vacuum leak, vs. say a fuel system problem?

Thanks for any input in advance!

 

It actually sounds like it might be running overly rich - at least when it exhibits the symptoms that you're talking about. With that theme in mind, I'd be thinking Fuel Pressure Regulator (at the front of the fuel rail), along with potentially the vacuum system that runs that regulator. Also, it could be a leaking fuel injector that's allowing some bypass into the airstream that's keeping you too rich at idle. Hence, when you're giving it 'gas', you're actually giving it enough 'air' to keep it running fairly well.

How is the performance when it runs well, and when it's doing it's thing? An overly rich mixture will quickly lead to pops and backfires when driven - and you don't even have to be driving it hard to do that. Particularly with your free-flow exhaust, I would expect that you'd be getting some signs of a rich mixture at pretty much all driving conditions. Fuel injectors on my 84SE were replaced at about 150k miles (at 194k now - original engine), and were causing hard starts due to leakdown, rich idle and poor fuel economy (normal range is about 16-18 in city, 22-24 highway; average about 17-18).

Also, what's your current fuel MPG? This can tell you something if you've seen the MPG drop rapidly for no apparent reason. Your exhaust would also smell heavily of gasoline (ok, it would smell MORE heavily of gasoline than usual!).

On the other end of the scale, a lean mixture would have the engine idle 'hunting' up and down about 100-200 rpm when static, but that doesn't sound like your issue.

Hey, I'm back - reread your thread and would also suggest getting under the front of the car and looking up into the air intake tube that goes from the radiator support to the air box. If you have something stuck up there, or a clogged air filter, it could cause some of the problems that you describe - poor A/F mixture.

 

i dont know much about fuelinjecton but could it be a stuck 2ndry injector? or port or whatever

 

If you're thinking it's a stuck '6'-port, I doubt it. The auxiliary ports are only open under full-throttle acceleration, and most SE owners are actually running around with them clogged shut due to carbon build-up, anyway - it's a performance hit, but actually increases fuel economy vs. having them working.

It won't cause idle issues or an inability to stay running if they're not working right, though.