Stumbling at low rpms-'88 3.2 Carrera

[JrodVW]

My fathers 1988 Carrera 3.2 has an odd stumbling problem. It occurs mainly under 2000 RPM and the car stumbles and hesitates. Over 2000 RPM everything is fine. There is no sign of running rich (no odors, or dirty exhaust)

The car runs flawlessly in the rest of the rev range with no other visible problems. This occurs in all gears, making take off from a stop light somewhat tricky. Previously he had a Weltmeister chip in the car, but took it out about 1,000 miles ago and the problem still persists. The car also has Magnecor wires, Bosch Platinum plugs, and a K&N Cone Filter. The car is always run with high test gas and has approx 56,000 miles on the clock.

Any ideas guys on what to look for? Perhaps a bad sensor? Running lean? Maybe it's an ignition problem?

edit: The car also has a dual outlet Fabiani exhaust, but retains the cats.

[Jim Smolka]

Though not likely, check the DME relay.
Check the cylinder head temp sensor.
Check inside the dizzy. Sometimes they get a little rustly inside and need to be cleaned
Could also be the speed sensor on the flywheel may need to be clean and adj or replaced.

Also, please update your profile to let us know where you live.

[Dan Owens]

Does it stumble all the time or only when you're light on the throttle. Does it run ok when you are more aggressive with the gas? Have a flat spot about 3500 to 4000 RPM? If so check the o2 sensor for replacement. Also check the head temp sensor too.

[JrodVW]

Actually the car stumbles most, as I said under 2000 RPMS, but with heavier throttle. A very light foot will get you throuh the stumbles, but you'd need to be on a flat road in 3rd or possibly 4th. IE: Light enough on the throttle that the car really won't accelerate at all.

The Cylinder Head Temp Sensor was replaced a few years ago. I printed out the DME trouble shooting chart, but we just don't have the tools to check many of the items.

I use a reputable VW/Audi/Porsche garage, Hodi's in Englishtown, NJ. His prices are more than fair, his work is excellent, and being an independant family owned shop, it's the type of place I like to help support. Perhaps I'll give them a call and run a few ideas by them, give them the diag charts and see what they find.

Oh, BTW: Look for my thread containing 16"s Fuchs in very nice condition with heat cycled A032R's with a good few months left of them.

[Dan Owens]

In that case I'd have them check the Air Flow Meter operation too.

[BGCarrera32]

Check your fuel pressure...

[stlrj]

The Platinum plugs might be the problem. Try a cheap set of conventional plugs.

Joe

[Sonic dB]

at 56K miles...if its original...it wouldnt hurt to change the O2 sensor...probably would help. I just yanked my old one out and the insides were just crusted white.

[zwhitea]

Hi there, I'm a bit new to this game, but your problem sounds very similar to what happened to my 1987 3.2... My problem was tracked to a faultering Air Flow Meter, which was diagnosed by an emmissions test.. Basically the car was running lean. A second hand AFM sorted me.

[ruf-porsche]

Loss of fuel rail vacuum source. Vacuum is supplied to the fuel pressure regulator and dampener to help tailor the fuel mixture according to engine load. as load goes up and vacuum decreases, fuel pressure and mixtures go up.

However if the lines or connection fail the vacuum signal is lost, fuel pressure and mixture will remain higher than usual under all conditions. With the addition of the unmetered air at idle a lean condition will occur.

The cause for this vacuum signasl loss is usually the failure of the connector at the vacuum dampener. It simply becomes soaked with oil vapor and expands, losing it seal at the dampener. This connector can be found at the forwardright side of the engine above number 6 cylinder.

Replacement is quite straightforward, after the air filter housing has been removed. The connector at the left side pressure regulator and the throttle body can also fail, but this is much less common.

After the appropriate repairs has been made the base idle fuel mixture should be reset and the hesistation should be gone

[JrodVW]

Excellent tech advice everybody. I'm going to print this out and systematically go through each item starting with simplest to hardest.

[Purrybonker]

ruf-porsche: is this the villain that you are referring to:



Thanks

Ken

[ruf-porsche]

Yep

Edit:

Didn't notice avtar

Why certainly

[Purrybonker]

oh, a wise guy, eh? why, I otta...

[Paul Franssen]

Kabonk... (outsider interpretation)

[ruf-porsche]

Originally posted by Purrybonker
oh, a wise guy, eh? why, I otta...

You otta what you numb skull?

Spread out

[CrossT]

I put a set of the platinum +4 plugs in one of my cars [though not a p-car] and did not like the way the car ran afterwards.

todd
86 cpe

[Otto]

Re-torqoe the intake manifolds. Check the runner boots for leaks with starting fluid while it is running. The engine will change its tune if you spray starting fluid in the suspect area.

[stlrj]

I can't understand why 911 engines are so spark plug sensitive, why Platinums will work or not work on some engines and regular plugs work where the Platinums failed. Installing Platinums in any other car import or domestic you would hardly notice any difference.

Maybe the problem that needs to be addressed is higher up on the list which may be the cause of a cascade of failures resulting in poor plug performance, like maybe the high quality but poor performing Beru ignition cables that we all assume are the best that your Porsche dollars can buy.

The reason I suspect the Beru cables to be the underlying problem is because of there intolerance to the slightest amount of water, meaning if you tried driving in a down pour or run your car through a car wash, you risk stalling your engine and if you're lucky getting it restarted again.

I don't know of any other car that would leave you is such an embarrasing situation after a simple car wash or down pour.

To prove my point, I replaced my Berus with Autolites a few months ago and noticed my plug failure problem has gone away, no longer stumbles when taking off regardless of what gear I'm in and my engine will keep idling when I hose it off which is something that has never happend before.

Just some thoughts,

Joe

[targa911man]

I agree you should check the above first, but here's another thought--maybe a weak alternator (or other cause of weak spark, maybe bad coil)? Doesn't generate enough spark at lower rpms, heavy foot causes flooding, light foot rations the gas so it can be burned.