Aw cr@p! What did I screw up now?!?

Weaver · 02-21-2005, 04:38 PM

I drove my '88 Carrera ( 80,600 miles ) for the second time this year after its winter tune up. Both times I started it this year it was about 40 degrees F out. Both times the idle immediatly does its own revving from 900 to 1200 rpm for about 30 to 45 seconds, then it levels out to 1100 rpm for a 1:30 then lowers itself to an "uneasy" 900 rpm. The first time I drove the car last weekend I tried to warm the car up as best as I could because it was terrible cold, and I was checking the oil level. While driving it bucked while pulling away from a stop once, but I just thought it was cold. Today, I let it idle of about two minutes then backed out of my driveway ( 160 feet ). The car would not stop bucking in any gear until around 4000 rpm, and got alittle better as it warmed up to 120-130 F oil temp. But it still bucked for about five miles of stop and go driving. Things I've done to the car:

Clutch 77.500 miles 7/30/03
SteveW chip & cat bypass 78,600 miles 9/04

Dist. cap & rotor
Magnacor wires
Bosch plugs
Cone air filter 80,550 miles 12-04 thru 2-05

Checked all of the plug wires, checked the connections to the injectors ans most of the wiring loom. I let the car sit for ten minutes then started it up and it idled at 900 and only bucked while getting hard on the throttle. The oil temp was still around 130F ( very cold here in Indy ).

After adding the SteveW chip, which I think is GREAT, the idle hunts only a little. Not enough to register on the tach, but it is audible. And I think its running alittle rich, heavier carbon deposits in the tail pipe.

I did remove the air flow meter from the engine. I didn't throw it across the room, but I also didn't place it on a pillow like a egg. I didn't think they were that fragile. Has anyone broken one of these?

So at 80k miles and only happening in cold weather, could it be the cylinder head temp sensor? A DME relay would not clear up while driving would it? Probably need to check the A/F mixture, don't I?

Sorry this is so long, thank for your time.

Weaver

Jim Smolka · 02-21-2005, 04:44 PM

Could be many things. 1st thing is to jumper the Fuel pump so that it is running all the time (jumper at the fuse panel). Place a fuel pressure gauge onto the car if possible. Then test drive. However, FP is probably OK.

If problem still exist, test the resistance of the engine temp senor.

If Ok, remove, clean, and set the gap on the 2 flywheel sensors (speed and reference)

Jim Smolka · 02-21-2005, 05:07 PM

Also, check that the large cable to the DME is tight. Sometimes, the cable's connector does not mate up well to the DME box. A large rubber band is a good trick. If that fixes the problem, then there many be a loose solder joint inside of the DME box.

creaturecat · 02-21-2005, 05:26 PM

could it be dampness inside the dist. cap?

88-diamondblue · 02-21-2005, 06:18 PM

Sound like what mine was doing this last spring. One night when I got home I looked in the engine compartment and it looked like a mini lighting show. The plug wires were bad. The original wires were on it with 79000 miles on them. If they have not been replaced its worth looking at.

soup dragon · 02-22-2005, 10:29 AM

When my dme relay was on the way out the idle was very erratic-going from normal rpm to almost 2k then dropping until the car nearly stalled.
The main symptom was the car intermittently refusing to start once it had become warmed up (driven somewhere parked up then went to go and no go!)

911mot · 911mot's Garage

I second dampness inside dizzy cap

Weaver · 02-22-2005, 04:36 PM

Thank you for everyone's replies.

So I've checked the dist. cap for condensation. Everything was dry and the cap and rotor are brand new.

The plug wires are brand new and I did not witness any arching.

I measured the resistance of the head temp sensor and it came up .65 ohms five or six times. Is .65 too low? I thought it needed to be between 1 and 2 ohms. I did find out that it is a single wire sensor and not the updated two sensor. Does this mean it might have a bad ground?

The fuel pump was replaced at 75k miles ( the car has 80,600 miles ) by the PO . But I have not replaced a fuel filter yet. Could this be a problem? I am at a quarter of a tank. Kinda low.

Thanks for the help.

Weaver · 02-22-2005, 05:05 PM

I just read in one of the Pelican tech articles that the sensor should read from 1 to 2 ohms of resistance and if the sensor has failed, it should be 0 or infinity. So if I got .65 ohm, does that mean my sensor is losing resistance? Does that make any sense? Am I measuring the resistance wrong?

curiousone940 · curiousone940's Garage

If you haven't driven the car more than twice this year, then that in and of itself could be part of the problem; change the fuel filter if it hasn't been changed in the last 2-3 years. On the CHT sensor, the measured resistance will be dependent upon the ambient (or actually, the cylinder head temp). Bentley will have those figures for you. If you have a known good DME relay, try switching to see if things improve. These are some of the known major "culprits" on this vintage P-car.

Steve Marshall · 02-22-2005, 06:37 PM

Every Porsche I have ever owned has bucked like that at some time or another. I wouldn't do a damn thing but drive it more and drive it hard.