svo2r

Hello to all,
I just purchased a 87 928 with 80k. It runs good except for when it's cold. It will ot take the gas and stumbles and runs rough. This gets better as the engine gets hotter. When it's hot it sometimes does it when I stab the trottle instead of easing into it. It also will stall for no reason while idling but starts back up after a moment of roughness. Any ideas and thoughts will be appreciated.

Rufus Sanders

Well, I don't have a clue, but i will add this question "does the 87 have a thermo time switch and temp 2 sensor?" If they do, I'sd start there, but some S4 owner would have to confirm this first. - Ruf

Jeff928S4

Bad plug wires arching?

Mass Air Flow Sensor? (this would be my guess, as mine does the same thing).

How does it start in the mornings? Does it fire right up or stall a few times like there is no gas getting to the plugs?

svo2r

It fires right up and idles fine. It's when I give it a little gas, it does not want to take it. I have to feather it a little or it will sputter. I checked all the hose and replaced the plugs, cap, rotor and wires.

Garth S

With the engine on a cold start up, it sounds like a defectiveTemp II sensor or its connecting wiring, or the cold start injector activated by the Temp II sensor is erratic. However, that does not explain the 'flat spot' off idle with a hot engine when the throttle is 'stabbed':
With the latter, could it be a faulty throttle position sensor/switch ?

Jim bailey - 928 International

No cold start injector after 1984 USA ..... temp sensor on thermostat housing talks to fuel injection brain ".I am cold , I am hot" . The Mass airflow sensor gives the injection brain the most significant and wide range of information about what the brain needs to do to inject the appropriate amounts of fuel. The temperature sensor 928 606 126 00 tells the brain "cold" so it adds more fuel for a rich mixture to keep it running better. Old carbs used a choke to restrict air flow when cold for the enrichment needed by a cold engine. L H injection is far more efficient as long as the various sensors do not tell lies to the brain.

Garth S

Whoops, an '87: yes, the lies told become more sophisticated ... but they are still lies.

svo2r

I thank everyone for their input. I am new to this car and need all the help I can get. Tonight I cranked the car up and revved it up a little and it stalled. Took me five tries to start it and to do it I have to floor the gas pedal. After it cranked I took it out and wound it up to 120mph and it runs better but still stalls after being cranked. If it helps, the exhaust is very hot like maybe a cat problem. Should I just start replacing stuff until I find the problem?

svo2r

It left me stranded today. It would crank up but idle very low and rough. It would stall as soon as I applied any throttle to it. After sitting for 30 minutes it cranks up and runs fine. Any ideas?

Thaddeus

Continue with the cheap and easy stuff for awhile. Try injector cleaner and replacing the fuel filter. If the injectors are dirty, they could be jammed "open"-- then they could be leaking when it's shut down, not closing all the way, so it's running way too rich, etc.

Run a bottle of techroline through it. It can't hurt.

macreel

rough idle, erratic power?

I'd look/listen for vacuum leaks, too.

G'luck.

jpitman2

Hot exhaust sounds like very lean mixture. Are the plugs white - should be milk coffee colour. When my CIS control went high and power was down, plugs were dead white. Fuel Filter is first easy candidate, then pressure test at the rails. Also check pressure regulator for leaking.
jp 83 Euro S AT 48k

Rich9928p

Have you checked the temperature sensor? If the ECU doesn't know that the engine is cold, it does not provide cold start enrichment and it will not start. Eventually after cranking enough, there may be enough “raw” fuel sprayed into the intake to start the engine. You would see smoke after starting because the fuel wasn’t metered properly.

The Temperature Switch II is located in the front center of the engine just to the right of the fuel pressure damper.

1. Check the plug to the sensor, is it on tight? Are the contacts clean? If not, clean the connectors and clip it on tightly. Check engine starting now. If it does, you’re done. If not got to step 2.

2. To check the temperature II sensor, you’ll need an ohm meter. Remove the connector from the ECU.

Refer to the attached documents for the connector type. Connect the ohm meter to

- pins 13 and 5 of the 35 pin LH connector (S4 and newer 928)
- pins 2 and 5 for a 25 pin LH connector (1984 – 86 Euro and 1985 – 86 US models).
- Pins 13 and 5 of the 35 in L-Jetronic connector (US spec 1980 – 1984)

Do not connect the ohm meter to the pins on the module itself. The correct value ranges are:

2.1) LH Jetronic:
0 C / 32 F: 4.4 - 6.0 k-ohm
15 – 30 C / 59 - 86 F: 1.4 to 3.6 k-ohm
40 C / 104 F: 0.9 – 1.3 k-ohm
60 C / 140 F: 480 – 720 ohm
80 C / 176 F: 250 – 390 ohm

2.2) L-Jet specs are:

2.21) Temp II sensor (gray plug):
10 C / 14 F 7 to 12 k-ohm
20 C / 68 F 2 to 3 k-ohm
80 C / 176 F 250 to 400 ohm

2.22) Cold start valve (brown plug):

Note: when the “connector locator notch protrudes inward to the pins from the top, the left pin is Terminal W and the right one is Terminal G.

Terminal “G” and “ground”
below 30 C / 86 F: 0 ohms
above 40 C / 104 F: 100 – 160 ohm

Terminal “W” and “ground”
below 30 C / 86 F: 0 ohms
above 40 C / 104 F: 100 – 160 ohm

Terminal “G” and terminal “W”
below 30 C / 86 F: 25 – 40 ohms
above 40 C / 104 F: 50 – 80 ohm

Since your problem is cold start, you could just look for the proper resistance range for the ambient temperature of the cold engine. If the sensor is shorted (zero ohms resistance) the mixture will be too lean and the engine will not start when cold. For others who may have problems at other engine temperatures, I’m including all of the resistance ranges for higher engine temperatures. If the sensor has an open circuit (infinite resistance), the fuel mixture will be too rich, the engine will not run when warm, and will be difficult to start when warm.

If the values aren’t correct, measure them directly at the Temperature Sensor II. You’ll see that there are two prongs on the sensor. There are two separate temperature sensors housed in the one sensor body, one for the LH and the other for the EZK or EZF module. Note the orientation of the protruding alignment notch on the outside of the sensor. If you are viewing the alignment notch orientated to the left side, the prong closest to you is the prong for the LH controller and the prong further away is for the EZK or EZF module. Clip one of the ohm meter leads to the prong closest to you (LH) and clip the other lead to a ground point [Do NOT connect the ohm meter leads between the two prongs of the sensor]. Repeat the resistance measurements.

If the resistance readings are in the correct range, there is a problem with wiring to the LH controller or the connector itself could be corroded. If the resistance readings are not correct range, the temperature sensor must be replaced.

Rich9928p

For those who own older 928s, use these diagrams.

svo2r

You people are the best. Even though I am mad at my Porsche, it's nice to know I can get so much help. I will be busy then let ya'll know what I come up with.