Spent about 3 hours in archives without success.

My car is now barely able to run. I bought it 4 months ago and it had run perfecty for the whole time - 5k miles worth. I have done a number of suggested maintenance as recommended on this list including vacuum hoses, etc.
The Problem: About 2 weeks ago, the car would sputter at about 2k rpm, like it was lugging. Each day, the problem got worse with the odd day where the car would run half decent. Now, the car will not stay running at all. I can start it but short of keeping the rpm over 3k, it will die. Even holding the rpm at 3 to 4 k, it has the miss and drops by about 1500 rpm, every couple seconds. It feels to me like one of 2 things, either fuel supply (changed relay, no help) or plugged cats (doesn't seem likely with 2 cats to react so drastic).
I am looking for some guidance - where should I start? Fuel filter, Kill the cats?

Thanks for all help!

 

Forget about the fuel filter and cats. The most likely problem is a vacuum leak.

 

check for dirt in your fuel tank - not nice work, but works wonders, particulalry if the car stood before you got it and now is put back into life

 

I am no mechanic, but I had similar symptoms with a different car and it turned out to be plugged cats. Can you hear the fuel pump when you turn on the key?

 

Ernest, Replaced all vacuum lines but I will put the guage back on if I can keep it running long enough. I wonder about dirty gas - will check filter, then tank. Perry, I would think that both cats would have to plug simultaneously to cause this problem - car ran awesome for the last couple months.

Warren

 

check the mass air as well. car will run filthy rich and not idle if it fails. i believe if you unplug it, the car should run better (although still not great, more of a limp home mode) if that's the culprit

 

ditto

 

I can hear the fuel pump when I turn on the key. I will try Tom's suggestion tonight and will also check the fuel filter. As for the cats, my plan was to eliminate them as part of a exhaust rework this winter. I may just undo the exhaust in front of them and see what happens - my teenage boys will love that

I still can not get my head around why both cats would plug simultaneously so bad that it will not run. I can see it when you only have one cat - I have had that happen with identical symptoms to what is happening now.

Thanks again - all suggestions appreciated.

 

I, too, seriously doubt it's the catalytic converters. Vacuum leaks or mass air flow. Make sure you check that vacuum pressure holds to the HVAC system, too, since that can affect the engine's vacuum needs.

 

Fuel filter change is cheap and easy.

A cheap-n-easy cat test is to drop the exhaust and then rev it a bit. Or just separate it at the exhaust manifolds and let those hang down.

 

Okay, So far plan of attack is:
Try unplugging MAF
Check vacuum
Replace Fuel Filter
Unhook Cats from system

Any other suggestions or should this cover it for a first go. I will update the list on Monday with my results.

Thanks again - I love this place almost as much as my car.

 

The MAF (amongst other things) can play strange tricks. Recently, 944S Boyee (Jeff) had a high and surgeing idle in the 1100 to 1800 rpm range. He tried unplugging the MAF with no effect, but swapping his MAF to my S4 gave a 'no-start' condition. When the reverse was done, his car ran as it should - an ~750 rpm idle, no surge. John Speake noted that unplugging the MAF to achieve better results tends to work if there were a gross failure: Jeff's cars condition was apparently not that far advanced. If searching the archives, check Rich9928p, John Speake for detailed MAF & LH info, of Jeff's thread for common symptoms.

 

Update
I finally got time to try all of the above suggestions.
First tried unplugging MAF - no change.
Checked vacuum, held at 15 psi.
Changed fuel filter - no change.
Unplugged exhaust in front of CATs - loud as hell but no change.
The car will idle for about 5 seconds, then dies. If I hold the RPM higher, it "misses" to drop about 1000 rpm before recovering. It really feels to me like fuel - could it be a fuel pump. Every time I have had a fuel pump problem, the car just dies altogether though. Any suggestions what to check next would be greatly appreciated.
Thanks,

Warren

 

One more update as part of this question. The HVAC side of the vacuum test showed 16 PSI and held there after I shut the car off. The other side, psgr side vacuum lines I tied together in a junction that I made acessible when I replaced all of the vacuum lines. Anyway, when I tested this side, the vacuum went to about 15 PSI but when I shut the car off, instantly went to zero. Can anyone tell me if this is right?
Thanks,
Warren

 

Warren, I'm not sure from your description exactly where you are testing. There is a check valve in the lines near the brake booster. Anything rearward of that(inside, HVAC vac reservoir, etc) should hold vacuum with the car stopped. I don't remember off the top of my head where the cruise solenoid is connected... IIRC it's not on the engine side of the check valve and it should hold vacuum as well, but I could be wrong on that. In any case, for diagnostic purposes you can just replace the check valve with a plug in the line leading to the engine, and completely eliminate the HVAC circuits.

Also check all of the rubber boots on your intake, make sure they are tight and not split.

HTH