poor idle at start-up
 

Here's the deal:

I have a 1985 late NA 944... During start-ups the idle is very rough for about 3-5 seconds. It does it warm or cold. I have checked the fuel system (did a complete overhaul on it...injectors, fuel lines, filter, pump....the works) and have new spark plugs and wires. Also, the battery is brand new. The car runs great, no hesitations or missing, and once the initial start-up is out of the way, the car idles fine.

There is one thing that I did to correct it. I replaced the ignition relay. The initial startup, after the relay was replaced, the car started without any problems. After that though, the problem came back and has been here since.

I have exhausted my mechanical experience and would be much obliged to any help!!!

I also get a rough idle just after startup if the car has not been started for a long time. I assume that it's just a matter of the A/F ratio (or fuel or spark control) not being ideal for the cold condition. Lots of engines are a bit rough before they get warmed up.

The only problem with this little theory is that it doesn't do it all the time so something must be different (not working right) to make the rough idle show up.

Could a bad temperature sender cause this? by sending the wrong signal to the DME. If the DME thought the engine was already warm it would use the fuel/timing map for a warm engine which would not work very well if the engine was actually still cold.

Just thinking out loud (and grasping at straws).

Is the temperature sensor the one in the side/back of the radiator (right below the upper hose)? If so, I just replaced it bc my cooling fans would not shut off.

No, I'm pretty sure the one on the radiator is just to control the cooling fans at the radiator.

I was talking about the regular temperature sender that goes to the DME & to the temp gauge at the dash. Honestly I haven't messed with it on my 944 so I don't even remember where it is.

I threw that sender question out hoping someone who actually knows the answer would chime in. . . .

The temp sensor for engine control is on top of the engine, under the coolant bleeder screw. It is a thermistor, resistance across it, measured with an ohm meter should vary with temperature. I have the table to compare temp to resistance somewhere in my notes and can look it up if you need.

Jon

I plan to check it out early tomorrow morning. I have a few other problems that I need to address (AC compressor clutch squealing mainly) and then I'll dive into this problem. Ill be sure to keep you posted incase I need the numbers.