Need Help w/Testing

[North Coast Cab]

I'm trying to diagnose some cold start and idle issues so I want to test my oxygen sensor and head temp sensor to eliminate them. Lots of info on the BBS, but still not exactly sure.
?
O2 Sensor - is it #3?

Looking for .2-.28 volts
How do I connect the volt meter?

Head Temp Sensor - is it #1?
Looking for Cold 2.5K ohms to 3.3K ohms, hot - 250 to 375 ohms
How do I connect the meter.

Thanks, John

[surflvr911sc]

The O2 sensor isn't there. #1 is the CHT sensor, I forget which is which but #2 & #3 are the speed sensor and the posstion sensor.

The O2 sensor is a black 3 prong plug on the left side. Look down by the valve cover toward the front.

EDIT: It might be easier to find if you first find where the wires go through the sheet metal and then follow it back to the plug.

[North Coast Cab]

Checked the Os sensor and read .86volts steady. Looks like things are a little rich.

Pulled the head temp sensor plug, #1 above, and car died. Hmmm....

Read across the #1 & #3 pins on the ISV and read .039

John

[North Coast Cab]

Clarification

On the ISV I read .039 from #1-#3
On the connector I read 0 from 1-2 & 12 from 2-3.

The head temp sensor read .736 ohms when not running. Looks like 1-2 is more normal. Any thoughts?

I really don't know what I'm doing.

John

[surflvr911sc]

Ohm the CHT, but it sounds like it's fine.

I don't know the numbers off the top of my head but the ISV can get gummed up, you might want to take it out and clean it. Check the idle switch on the throttle too.

[surflvr911sc]

Originally posted by North Coast Cab
I really don't know what I'm doing.

me either

[North Coast Cab]

Ryan,
Already cleaned up the ISV this morning, it looked ok and still runs the same.

Looks like the O2 and head temp sensors are ok. Not really sire about the ISV, need a little more research.

John

[Lorenfb]

You're correct about the mixture, .86 volts @ the O2 is on the rich side.
Ideally it should be about .50 volts which matches the DME neutral value.

Removal of the temp sensor will cause the engine to die on 3.2 engines
when warm. The value of the sensor should be about 300 to 350 ohms
hot.

The resistance reading of the ISV across the outer pins is about 40 ohms
(.040 kohms). It's half that value between the center pin and the outer ones.

To diagnose your problem, you need to check a number of other things:
1. the fuel pressure
2. that the AFM has not been misadjusted
3. the idle throttle switch is closing
4. the idle valve is not carboned-up
5. the DME has a stock Porsche chip
6. the internal DME switch is set fully counterclockwise

[North Coast Cab]

Loren,
Where is the idle throttle switch and how do I check it for closing. I haven't touched the mix screw, don't even really know where it is.
I'll pull the seat and check the DME settings.

John

[Lorenfb]

The idle switch is on the throttle body with WOT switch. The easiest way to check
the idle switch is on the DME connector between pins 2 & 5. The idle switch should
be closed and then open with a small movement of the throttle linkage.

Your problem sounds as if it's the same as from the other thread?

"High Idle

Finally got the engine back in and the P-car running. Everything is great except for a high idle. Since it's a DME car I really don't want to mess with anything. I was planning on having the mixture set soon anyway, but I'd like to get this sorted out first. Ideas?

John"

[North Coast Cab]

I leaned it out a little to get the O@ reading somewhere in the middle, fluctuated between .35 & .65. I took it for a drive anf then fine tuned the idle. Then I shut it down and let it cool for several hours. Just went out and it fired right up. Looks like the problem has been solved. Now I'll take it to my p-mechanic and have him do the CO mis the right way.

John

[North Coast Cab]

I moved this to a new post.

Well after a few days the car is still not running well at start-up. Really stumbles and won't idle. Revs a little like it s really missing, even giving it a little gas. Once it runs for 10 seconds it will idle, though fairly low.

Here's where I stand.

Reinstalled stock chip
Adjusted idle back up with engine warm.

Checked mixture with voltmeter at O2 sensor. Was .86 volts, leaned out slightly to get more within range.

Checked Idle Control Valve
Voltage as specified across pins.
Removed and cleaned just in case.
I can hear the click of the ICV once throttle is moved

Head Temp Sensor
Appropriate reads when engine hot

Fuel Pressure - I don't know how to check.

DME Switch is set at #3
Should it be fully counter clockwise or to #1?

When warm idle fluctuates a little up and down, you can hear it more then you can see it.

John

[Steve W]

DME switch position 3 leans out the overall fuel mixture - that may have been one of your problems. Turn it back full counterclockwise, that's where it should be.

[Lorenfb]

Unplug the temp sensor when really cold (not when warm/hot or the engine will be
too rich). This will compensate for a low fuel pressure or other fuel factors possibly
causing a bad idle/miss at startup. Only leave it unplugged for a short time to test
for your problem.

Also, check that the spark from the coil jumps 1" to the engine case. Then check
the cap & rotor. Check out this web site (www.systemsc.com) on the Diagnostics
page for some additional ideas.

[kjb]

Check for broken wires in any connectors.

My friend's 964 has had really bad idle problems for about a year: it turned out a wire had broken inside the connector to the air-flow meter.

It's amazing the thing would even start with the wire hanging loose. Now it goes like stink again!

good luck,

Johan

[North Coast Cab]

I'll change the DME swicth and see how it starts. If problem persists I'll disconnect the temp sensor at start-up and see how it reacts to that. After that I'll check the coil for spark. When the engine was out I installed new Magnecors, so I don't think that is the problem. Magnecor connectors do not come off like the stock ones do so they really can't be loose. Cap and rotor only have 5,000' miles on them, but I do have the old one to try if need be. Thanks to all for the help.

It's frustrating since I did the first engine drop w/new clutch and a ton of other things and this is the only problem I'm having. I still have 2 1/2 weeks before my first DE so the pressure isn't on yet.

John

[North Coast Cab]

Everything checks out fine. Moved the DME switch fully counterclockwise, double checked and slightly adjusted mix via O2 voltage, Unpluged temp sensor when cold, and checked coil spark.
I have one thought though. During my engine removal I broke one of the tits off the ambient air valve, see below

I replaced it with part #H-207-227-02 from Pelican. It looks functionally the same, but is definitely not exact. The new one has a metal top and no mounting hole. Anyway, there are no arrow directionals, is it possible this could be in backwards and therefore chocking the engine when cold?

Again, problem exists only when cold starting. Stumbles, sounds like it's running on 3 cylinders, and won't idle unless you hold gas for 10-20 seconds. Hunts very badly at start-up. After 30 seconds it idles and runs fine, though there is still a slight hunt.

John

[Lorenfb]

That unit you show bleeds air into the throttle body. It's probably the EGR
valve. If air enters the throttle body when the engine is cold, this would
significantly affect the colding running mode.

Try pinching-off the hose and see if the problem gets fixed.

[North Coast Cab]

I tried to start clamping either side of the ambient air valve thinking it may be opening or closing inappropriately. No change.

I disconnected the head temp sensor connection as suggested when ice cold and it won't start. Tries a little but will not start at all. Is this good or bad? Smells like gas.

Rechecked the head temp readings, cold 647ohms, hot 3500ohms. They seem a little out of the range. What do you think?

Thinking about the ICV some more. Does it only control the speed? When it starts it's not a idle speed issue, it is a bad miss and no or poor idle for 20 seconds.

John

[Steve W]

John, it seems your head temp sensor reads way out of wack. Are you sure you are reading it correctly? It should read 3000+ ohms cold, and around 300 ohm+- when hot. If the impedance reads as low as 647 ohms cold, it will be very lean on start up, and 3500 ohms cold will try to run rich at normal running temps, however the O2 sensor may mask a lot of the richness because it is trying to lean it out. You said you replaced the head temp sensor before, so you may want to check out the wiring.

edit: if you replaced with a new 2 wire head temp sensor, make sure one of the wires, which should be ground, is grounded properly.