Hello,

I am back again. I have a chronic problem when the engine runs hot, especially on the 90+ days we had this past weekend. 1972 FI 1.7

When the engine gets good and hot my curb idle drops about 700 RPM to about 300 RPM on the verge of a stall.

Took it to the Porsche dealer and they did a complete tune up, replaced the deaccel valve, replaced breather tubes, etc. O' and they cranked up the idle. Originally they were fixated on the fuel pump being affected by the engine temperature so they crafted a heat shield for the pump.

The fundamental underlying hot idle problem remains. It seems as though we are just masking the problem. Is this something I should just learn to live with? Should I expect that the engine to stall everytime it gets good and hot?

There must be someone somewhere in the world that can help diagnos my problem.
Thanks!

Cylinder Head Temp (CHT) Sensor is suspect.

measure its hot and cold resistance and compare those values to the nominal good values on Brad Anders' D-Jet page - which i thought i knew the URL - but i don't... the guys with D-Jet cars have it bookmarked tho :-)

a search will turn it up in a hurry.

CHT resistance values are here: http://members.rennlist.com/pbanders/DJetP...tm#troubleshoot

Here they are:
CHT should be about 2.5 K ohms at 68 deg. F, less than 100 ohms with hot engine.

Excuse me? The CHT sensor is one of the LAST things I'd look at. Operates only in warmup, and is fully up by the time you've gone a couple of miles. Make sure the valve adjustment is correct. Look at the distributor, make sure the point plate is in good shape with a good ground wire and no slop. Check the dwell and timing, fully warmed up. Check the throttle switch for function and adjustment. Check the AAR. if you have an adjustable ECU, make sure the idle mixture is OK. Check the MPS, check the grounds, check the charging voltage. Make sure the fuel pressure is right. Then you might test the T sensor 1, which is in the intake manifold. Use Brad Anders' nice MPC EFI troubleshooting guide, mentioned elsewhere on this board. The Cap'n

Cap'n rocks! Highly informative!

10 more rants like that, and you'll have all you need to know about 914s, and a sore ass!


M

QUOTE (Cap'n Krusty @ Jun 28 2005, 03:41 PM)

...Operates only in warmup, and is fully up by the time you've gone a couple of miles.

sure, i agree.
but since the CHT sensor is what tells the ECU the engine is warm, if the sensor is bad (open or become disconnected...), the engine will be fed a warmup-rich mixture long after it has need of it.

i agree all that other stuff should be checked too, but putting an ohmmeter on the sensor is quick and easy. if it's in spec, move on...

QUOTE (ArtechnikA @ Jun 28 2005, 02:23 PM)

QUOTE (Cap'n Krusty @ Jun 28 2005, 03:41 PM) ...Operates only in warmup, and is fully up by the time you've gone a couple of miles. sure, i agree. but since the CHT sensor is what tells the ECU the engine is warm, if the sensor is bad (open or become disconnected...), the engine will be fed a warmup-rich mixture long after it has need of it. i agree all that other stuff should be checked too, but putting an ohmmeter on the sensor is quick and easy. if it's in spec, move on...

If it's open or shorted, the 2 most common failure modes, it won't even run, hot or cold. The Cap'n

being the distributor god on this site, I'm going to wager my 2 cents toward a stuck advance plate or stuck centrifugal advance......


yeah.

ALWAYS OIL THE PAD.....and run spyware and antivirus checks on your computer

AND the idle MUST be set when the engine is hot! not when its half assed warm or cold.

I have the same problem. Did you know if he had found a solution.

Before I make a suggestion, I'm assuming all of the components in your charging system have been checked and are operating correctly, your ignition timing and dwell are set correctly and that your mechanical and vacuum adv/retard is working correctly, you cap, rotor, and plug wires are all in good shape, all of the components in your FI system are present and have been checked (see my web page) for proper operation, all of your hoses are present and in good shape, and are routed correctly and have no leaks, your valve clearance is set correctly, your compression is good, and that your plugs are in good shape and gapped correctly. Unless all of this stuff is right, advice on solutions won't help you much.

What does your idle CO measure when the car is fully warmed up? How does that compare to the specification for your 1.7L? If it's too rich or lean you're going to have idle issues. If your CO is out of adjustment, if you have an ECU with a idle mixture knob on it, you can set it to the correct level. If you have to turn it all the way, either way to get to the correct CO, then your MPS is either out of adjustment or defective, and must be either replaced or adjusted (stuff on my page about this).

I should have been more specific.
My engine is a 2.0L with EMPI carburators.

-Advance/retard is not plugged… mechanics told me it was not a problem if I was not aiming for performance. ( I must admit that I am not sure that I can fully trust him for my 914)
- Carburators tunning has been done
- Timing has been done
- Valve adjustment has been done (not sure if the mechanics did the TDC methods)
- No vaccum leak could be found
- Points, rotor, rotor cap are good.
- Routing of the hose has been done by Chris Foley, I suppose it is good.
- I have no idea of the compression

From my readings.
- Can it be a vapor lock? Bubble in hot gasoline, the pump is pumping air (I don’t hear any squeak sound)
- Can it be that the valve expand when heated and become too tight?
- Can a coil or condenser failed while getting hot?
- Do I need a working adv/retard?