'84 passed smog, now it hesitates really bad.

[450knotOffice]

Guys, last week I had the '84 Carrera smog checked and it passed with flying colors. It has run very well and smoothly for quite some time. However, now that the smog check has been completed, the car has developed a really bad stumble/hesitation from 3200 RPM to about 5000 PM, then it clears it's throat and pulls hard to red line. It happens at part throttle and full throttle but is worse at full throttle. It just falls flat on it's face.

The guy who gave me the smog check had the car idling for about 10 minutes straight before he administered the test (even though the engine had been brought up to normal operating temp by me already). I'm assuming he was making sure the Cat was nice and hot for the test. By the time the test was conducted the oil temp had gotten really warm, although nowhere near the red zone.

The O2 sensor is new so I don't think that is it, but I'm trying to figure out what might be causing this and why it happened suddenly after I had a smog check? Could it simply be plugs that became fouled by the long idle time?

Ideas?

[stlrj]

It may just be a coincidence. An ignition miss from a bad plug wire, plug connector or plug can happen any time.

Meanwhile, you might check your plug connectors to make sure they're snapped securly on the plugs.

[84porsche]

Scott,

Always happens when you bring a new relative home. She just needs to get used to who she is sharing the garage with. They are siblings and they do get jealous.

[Joe Bob]

Checked the fuel filter?

[450knotOffice]

Thanks stlrj. I'll check everything obvious tomorrow.

Fuel filter...that's an idea. I have not checked that and god only knows how old it is. I've had the car for two years and more than 10,000 miles and haven't even thought of it.

Chis,..., yes they are...

I just want her smooth running engine back though.

[bigrubberjeep]

Try DME relay too. $42.00

[450knotOffice]

DME relay. Interesting idea. I replaced mine a couple of years ago just to set a baseline but kept the old one. I'll try a swap.

[anthony]

Idling for 10 minutes straight shouldn't be a problem for our cars at all.

[PatrickB]

Do the basic easy stuff... Check the plugs, plug wires, change the fuel filter, then an Italian tune-up is in order.... I can say that, because I'm half Italian!

If it still stumbles, I'd be happy to take it for a spin with you Scott, to throw in my diagnostic $.02... As you know, I've been down the "stumbling road" before...

[450knotOffice]

Thanks Patick. I hope it's something simple. I need to get out into the garage (in this un-godly heat) to check it out.

[Zeke]

Fuel filter symptoms starve the motor all the way to red line, not at part throttle and not at mid RPM's. That's speaking in principle only.

Smog guys shouldn't have their mitts in there except to clamp their lead to a plug wire. That's about the extent of correlative incidence other than the cat getting really warm with no circulating air around it. So don't count the O2 sensor out.

Listen to me, I've never owned a 911 with an O2 sensor. I know nothing.

[450knotOffice]

(chuckle)

Thanks Milt. You're right about the tech and what he did. I opened the deck lid for him and then he just looked around in there without touching anything other than one of the spark plug leads to put the clamp on. The engine runs really smoothly at idle and below about 3000 RPM but when I get into the gas it behaves as if it's leaning out in a huge way and stumbles as if it's trying to catch it's breath. If I stay in it, it'll continue this until maybe 5000 RPM or so and then clear it's throat and all of a sudden I've got the full power rush to redline. Shift up a gear and I'm right back into the stumble again.

[nostatic]

it knows about the 996...

[anthony]

Maybe you should check all the vacuum hoses in the engine compartment?

I've seen smog guys remove hoses and pulll a vacuum on the hose with a handheld gauge. I'm not sure what they are testing though.

[450knotOffice]

Update.

Alright, now this is getting kind of strange. I took a good long look at the engine today and saw nothing out of the ordinary. I wiggled the coil leads and they were tight. All of the plug leads were checked for tightness and, just in case, I removed and then reattached the #4 plug lead since that was the one the smog tech had attached his test lead to. I poked and prodded at all of the vacuum lines and pushed and pulled on the intake from the AFM down to the throttle body. I checked the tightness of the O2 sensor lead and it seemed tight. I thought "what the heck, I'll just disconnect the O2 sensor, take a drive with it out of the loop and see what happens", which I did.

Well, the car drove perfectly right from the get-go, from cold to hot. Smooth as silk all the way from idle to redline every time. I thought, "cool, I found my problem." So I pulled over and decided to reconnect it and see if the problem resurfaced. I reconnected it and took of again. It still ran perfectly.

Huh?

What the heck could be going on here? The car is acting like it never had a stumble at all. Could this be a sign that my DME relay is starting to fail? Or do you think my poking and podding of the plug leads had something to do with it. This is a little strange, but hey, I'm happy that it's running normally again, at least for now.

[Joe Bob]

Snot in the tank?

[PatrickB]

Remember mine Scott?

My rough running started completely out of no where... Intermittant at the beginning. It would often correct itself out of nowhere, as quickly as it would start screwing up... Poked, prodded, put in new parts, swapped known good parts when the problem was present, all to no avail... In the end, it became a constant rough running issue... The culprit??? - 2 bad fuel injectors. I ended up putting in a complete new set. The car runs better now at 145k miles, then when I purchased it with <70k miles! I also picked up about a 3 mpg increase in fuel economy almost instantly!

[450knotOffice]

That's right. I remember that. So your injectors were going bad, eh? Those darn things are pretty expensive though, right?

[PatrickB]

Originally posted by 450knotOffice
That's right. I remember that. So your injectors were going bad, eh? Those darn things are pretty expensive though, right?

YES!

Purchased from our host,
they are $144 each

All I can say though, is my car went from what felt like it was running on 5 cylinders, to what felt like was a new motor running on 6!

[bigrubberjeep]

Well since this issue was taken care of maybe I could bug you guys for help with mine, my motor is cutting out (never in first gear) once I shift in to second and go over 2K RPM it just dies, not a slow put put like gas starvation would but more of a electrical on/off type of thing, so I put a brand new DME in and still same sysmptoms.

What gives?