jheis

Car is an '89 5 speed which I've had for about two years.

I've got a couple of problems which may - or may not be inter-related.

It's had a cold start idle problem since I've had the car. It would start right up, but would stumble/stall if I tried to drive off. Replaced the Temp II sensor - no help. Car does not like to move when it's cold.

Recently the car started stalling out when I came to a stop. Would not hold idle - sometime it would stall 3 times while waiting for a light to change - tried to feather the throttle, but if it dropped below 1,000, I couldn't catch it and it would stall. Sometimes when driving at highway speeds, I'd get the sensation that it was trying to stall between shifts (whenever the clutch pedal was in).

About two weeks ago it cut out on me at freeway speed. Steady throttle or maybe even accelerating when it died. I was heading for the shoulder when it fired up again - cut out for maybe 30-40 seconds. Ran normally the rest of the way home (10 miles).

About a week later it cut out again at about 30 mph while accelerating on a city street. Coasted to the stop sign, hit the starter and it started right up again. Stopped at the grocery store, stalled pulling out of the driveway, started right up again. Stalled again at the first stop sign. Car would start right up, but wouldn't rev. Sat at the stop sign for maybe 5 minutes. Car would start and stall, start and stall. Was not responding to throttle inputs - at all. Start, but would not rev above 1,000 rpm. I was thinking I needed to call a tow truck when it started and responded to the throttle. Stalled again at the next stop sign, but started right up and responded to the throttle. Ran fine the rest of the way home (10 miles).

Today I had to make a run into San Francisco (110 miles round trip). I was about 10 miles out of the City when the car died out on me at a steady 70 mph. I coasted over to the shoulder and went through the start/stall routine again for about five minutes. Finally got it to rev above 1,000 rpm and proceeded across the GG Bridge hugging the right hand lane. I was caught in bumper to bumper traffic on the bridge approach. Car either stalled or idled at 1,300 rpm. Fortunately I was heading downhill and traffic was barely moving.

I managed to limp across the bridge - car was kind of bucking a little on acceleration, but not stalling.

Return trip - car was bucking like it wasn't getting fuel, but it didn't cut out. I was low on fuel, so pulled into a gas station for a splash and go.

With some gas in the tank, the bucking stopped and the car ran pretty good the rest of the way home - except for stalling every time I came to a stop...

I'm thinking I've got a couple of problems. Probably bad ISV. Bill Ball ran Theo's scanner on my car last weekend. It didn't return any codes, but the TPS wasn't working at wide open throttle. So, need a new TPS. I'm thinking the bucking like it wasn't getting fuel may be the in tank pump when the fuel level is low.

I have no clue what is causing the car to cut out under power - it's done it three times now - or why it will start but not rev.

James

Bill Ball

Hi James:

I hope others jump in with ideas. The 928 diagnostics we ran also showed a Hall sender fault. The sender wire and plug looked fine. Although some have reported drivability problems with a "bad" Hall sender, I would only expect 6 degrees of ignition retard at higher RPMs from that - hardly noticeable under routine street driving.

I could throw out a number of fuel and ignition parts as suspects, but nothing I know really fits very well with what you are reporting. A bad ISV would account for idle issues but not higher speed stalling or inability to rev. The failed WOT switch is another item that would not be noticeable except perhaps under WOT. I drove my car 145 MPH average speed for 100 miles with an inoperable WOT switch and only suffered mild overheating.

Perhaps your fuel pump is going through some odd, intermittent death throes.

Mrmerlin

does the car have an internal fuel tank pump if so then it may be clogged

FiveElements

It may be ideal to buy a $20 fuel pressure gage for the engine fuel loop. That way you can watch if there are unwarranted fuel pressure drops due to failing fuel pump or clogged filters. You could have failing fuel pressure regulators/dampeners or something weird like a corroded ignition coil wire that is causing weak spark. Or you could have a loose connection to some of the temp sensors. Dang... the list goes on and on.

JakeS2

This is one interesting topic. If we have electronic skill -happy people here it would be cool to have a electronic display showing this on dash or something, any volunteers?

SteveG

Check coil wires and clean coil grounds. Pull the coil wires out of their plugs and and check for corrosion.

jheis

Thanks for the input guys.

I think I've got a new fuel filter (external) in my parts stash. I have no idea when the filter was last changed. Can't do any harm....

James

newworld

here my 2 cents from wrenching a variety of porsches. its not your fuel pump. your fuel pump either works or it doesnt. yes sometime it can clog etc, but these porsche fuel pumps are rock solid. so are the starters bosch.

what has a tendency to happen with weird intermittent cut outs etc, many people say "vacuum" it could be but i never found one.

my culprits are electrical. the biggest one is voltage, sudden drops in voltage shuts your fuel pump. many times its a bad ecu.

i had porsches stall at traffic lights, etc but would run fine everywhere else.

if its cps its related to fuel. if no cps signal cuts fuel.

what i am saying is your fuel is most likely ok, its whats cuts that supply of power to pump thats an issue.

so electrical:

-cps
-ecu
-maf
-relays or even connections from relay behind the box....etc so its intermittent and sometimes loses the "grip" ive had that as well and hard to track down

Mrmerlin

FWIW if this car has an internal tank fuel pump,
then these have a history of the transit hose failing and clogging the pump,thus a reduced fuel flow.
Some have removed the pump and refitted a new hose ,
others have removed the pump and replaced it with the fuel strainer.

Bill Ball

Well, l would certainly replace the fuel filter and examine the in-tank pump, even though it's hard to imagine this causing an intermittent failure. If it's a CPS failure, there would be no spark. There is a 2-prong plug for the CPS near the CE panel that has a green and a white wire. I suppose that could be "loose" and intermittently lose contact. As well, there could be intermittent wiring faults in the MAF plug and harness (I've seen that, but in that instance the car would suddenly run very rich).

Your car started, idled and had very good throttle response when we tested it on Saturday at Sharks in the Park. We did find the WOT switch and Hall sender faults, and I thought the idle was not very smooth. Then, you had the intermittent failure again a day or two later.

It's worth checking the ignition system components, all grounds (particularly the FI grounds under the air filter box, and the engine block ground - perhaps one is loose and intermittently loses contact), as well as the relevant relays (EZK, LH, FP) and the FP fuse and their sockets, and consider pulling the CE panel down to examine the wiring behind it. Maybe we can get together soon and give it a more thorough check.

jheis

Thanks Bill

I replaced all the "53" relays with new ones shortly after I bought the car, but haven't done anything else with the CE - other than check the draw at each fuse (I also have the intermittent battery drain problem).

By the way, when the car does idle, it's what I'd describe as as a "loping" idle. Drops to about 400 almost stalls then bounces back to about 800 - repeat. Other times it holds steady at 750 - except for that spell yesterday when it was either stalling or idling at 1,300....

Last major repair by the prior owner before I bought the car was a new fuel injection brain done at Sonnen - so, hopefully, that's not part of the problem.

I've got a new ISV, but have to get a TPS and Hall sensor along with the hoses and all the other WYIT stuff to address when the intake is off.

I appreciate your offer of help. I'll take all the help I can get - I'm pretty much stumped on this one.

James

Bill Ball

The idle issue you describe above sounds like ISV.

My LH brain failed 8 or 9 years ago. At that time, there were only Porsche rebuilts. That's what I got for $1100 then, and it is working fine. However, I have a spare LH we could swap into your car for a test.

Although there are lots of things to check, the erratic behavior doesn't point to anything specific in my mind.

Let me know when you have a day free. At some point we need to get to teh Hall sender, and it's likely you need an ISV (did you try the WD-40 temporary fix?), but we should pursue other things first.

jheis

The fuel injection brain was done in Nov, 2006, although the car was only driven about 5,000 miles from that time until I bought it in May, 2011. Part number was 928.618.123.NX - which may indicate a rebuild - don't know. Sonnen's charge for the part was $1,150 in 2006.

I tried the WD-40 fix once, but I'm not a big WD-40 fan, so I switched to Marvel Mystery Oil (they're both, primarily, Stoddard solvent). I've run at least a quart of MMO through it an ounce or two at a time. I even poured in a couple of ounces before I left the parking garage in SF yesterday. I think the ISV is toast. As I said, I've got a new one, but need to source the other parts before we tear into it.

James

Mrmerlin

maybe you will find a cracked hose that connects to the ISV.

also get the two plastic connectors that plug into the sides of the MAF boot,
they seem to crumble when you look at them

jheis

Thanks Stan. Will do.

James