Engine hard to start at times, also runs rough at idle

suspect low fuel pressure to the injectors
run the fault codes to determine where the fault may be before you spend money

Not sure if this will help you out.Troubleshooting starting and running problems can sometimes be quite difficult. This is especially true if you aren't aware if all the possible causes of a problem. This is a general guide which will list symptoms for 944 starting and running problems and common causes of those problems. It is intended to help you map out a troubleshooting plan.
Running Problems

1. Rough Idle
   1. If the car starts when cold but, idles rough or does not want to stay running, this can indicate a problem with the engine temperature sensor. When the engine is started cold, the engine temperature sensor sends a signal to the DME control unit to provide a richer mixture. As the engine temperature sensor starts to fail, it sends a higher than actual temperature signal to the DME control unit. The DME control unit leans the fuel mixture thinking the engine is at normal operating temperature. This causes the engine to run rough. As the engine warms, it not longer needs the richer cold idle mixture and the engine runs smoother.
   2. If the car idles rough this can also be indicative of bad plug wires, distributor, or rotor. One way to check for bad plug wires is to inspect the plug wire runs with the car running in a very dark area. If the plug wires are bad you should see some arching to the cylinder head or fuel rail.
   3. If the car idles rough or cuts off at low RPM or idle, the cause could be a failing O2 sensor. The O2 sensor is out of the loop at full throttle and will not affect the way the car runs.
   4. A rough idle can also be caused by a problem with the air flow box. The damper for the air flow box can fail mechanically or the contacts inside the box can get dirty and send a errant signal to the DME control unit. This can sometimes be corrected by cleaning the electrical contacts inside the air box. This requires removing the cover on the air box which is held in place by caulk. You will need to cut through the caulk and gently pry the cover off. Once the cover is removed, clean the circuit board inside with a good contact cleaner. When you have finished cleaning the circuit board, reattach the cover using a non-corrosive caulk.
   5. If the car experiences a rough idle or idle fluctuates several hundred RPM, this can indicate a sticking idle stabilizer valve. Many people have removed and cleaned them but, this is normally a temporary fix and the valve should be replaced. A faulty O2 sensor can also cause RPM to fluctuate at idle. Unplug the O2 sensor and see if the idle still fluctuates.
2. Difficult Starting
   1. If the car is difficult to crank after sitting for more than several hours, the fuel return regulator or fuel pump check valve could be faulty. This will allow the fuel rail to depressurize and it takes some time for the fuel pump to increase fuel rail pressure sufficiently to fire the car.
   2. If the car is difficult to start when warm, again the fuel pump check valve, fuel return regulator, or individual fuel injectors could be leaking. The fuel pump check valve or the fuel return regulator leaking allows the fuel to drain back to the gas tank depressurizing the fuel rail. When the car is warm, the fuel remaining in the fuel rail can flash causing vapor lock. There are several ways to check this. One is to connect a fuel pressure gauge at the fuel rail. Start the car, let it run until fuel pressure is stable, then shut down the car and monitor the pressure at the fuel rail. With the car not running, the pressure at the fuel rail should not decrease to less than 15 psig. If it starts to decrease, clamp the rubber part of the line from the fuel return regulator to the gas tank and see if it stops the pressure decrease. If not, clamp the line at the discharge of the fuel pump and see if it stops the pressure decrease. An individual fuel injector leaking can depressurize the fuel rail and cause the same problem.
   3. If the car starts easily when cold, but is difficult to start when warm a failing DME relay could be causing the problem. As the DME relay starts to fail, it operates at a higher temperature. If the car is stopped, the higher temperature of the relay creates a high enough resistance to keep the relay from picking up when the car is started again. When the relay cools and the resistance decreases, the relay will again function normally.
   4. If the car is very hard to start or only fires part of the time and then dies it could be a problem with the distributor cap or rotor. 944 rotors are notorious for having the set screw back out of the rotor allowing it to spin on the end of the camshaft. When this happens the car will not fire at all or will fire momentarily when the rotor is in line with the correct cylinder to be fired.
   5. If the car is difficult to start when cold it could be a problem with the engine speed or reference sensors. One of the sensors sends a signal to the DME for TDC and the other an engine speed signal. The DME uses these signals to time the pulses to the ignition coil and the firing of the fuel injectors. If the sensors do not send the proper signal to the DME the normal result is a failure to get proper spark from the ignition coil. Sometimes their failure may be a result of debris building up on the ends of the sensors which reduces the gap between the sensor and the flywheel. If so, cleaning the ends of the sensor may get them working again.
   6. If the car is difficult to start or will not start at all regardless of operating temperature, there are a number of problems which could be causing this. Here is a list of possible causes:
      • DME Control Unit
      • DME Relay
      • Security System Control Unit
      • Fuel Pump
      • Fuel Pump Fuse
      • Distributor Cap, Rotor, Coil, or Primary Coil Wire
      • Engine Speed and/or Reference Sensors
      A fuel pressure gauge, spark tester, and voltmeter are extremely useful in narrowing down the possible causes of the problem.

Clark's Garage © 1998..
or try this link. What causes low rpm at the initial start of the engine Google Search

Well iv had this problem a few times in the past so will let you try some of them ,
1/ Fuel pump in fuel tank overheating ORfuel filter not letting fuel passing ,ANSWER remove fuel pipe to engine and feed into a bottle turn on key and see how much fuel comes out without stopping, if ok go to fuel tank and check the breather pipe (make sure its clear).
2/ If engine runs well when you first start without missing and idles well,but then dies at 15minutes
when you try to start again dose it seem to turn over faster or slower?
3/When engine running check the rear tail pipe on exhaust check for smoke and put you hand over the pipe hard to stop fumes (dose engine run rough and stop?),as the muffler or converter can be blocked more so when hot.{use a glove on your hand}.
4/When the engine stops take out No1 plug lead and fit a spare plug in it and lay on top of engine and spin engine over ,does it spark?? as it could be the coil overheating which would also do it if no spark.
5/ Chech coolant sensorplug for bad fitting Also check Crank Sencer and coil wire to distributor.
Let me know the results Ron

From what you are describing i feel you might be having an bad EGR valve..It only causes the rough idle and shaking and fuel smell in exhaust..It can also cause back firing. Does it happen? Also do you hear any popping noise from exhaust?

the problem will be faulty injector tips squirting and not atomizing take it to an accredited diesel specialist shop and have the new tips fitted and the injectors recalibrated

I also have a saab 900 s with the 2.3 L. I started throwing the same code. I found out from the Hanes manual that the CMP sensor is integrated into the distributor on this model. Which explains why the distributor costs so much. You might want to check your distributor out and makes sure their is no oil in the cap and that the black electric plug is fit on correctly. If it's okay just watch for rough idle (that's what mine started doing), unfortunately it looks like if your cam position sensor needs to be replaced you have to replace the entire distributor.

Have you had your mass air meter checked or replaced? This is the unit attached to the air intake hose behind your air filter. It senses the air temperature, speed, density, etc... and adjusts the fuel/air ratio to keep the vehicle running at "peak" performance. Also, check your TPS (throttle positioning sensor) it can also cause the problem you speak of. The TPS adjusts your engine speed/idle etc. and also compensates for hot/cold changes etc. This is roughly a $35.00 part and in most cases usually an easy fix.

Flashing check engine light is missfire, fuel pump probably causing multiple tries to start.Having to build fuel preasure,vac leak on one side of intake probably causing rich/lean condition.Also check back preasure to cat ,Sound like you are moving down right track.Mas air flow would probably set lean code bank1 and lean code bank2

I have a 1994 Cadillac Eldorado and every time i start it the car has rough Idle and the Idle fluctuate's. I also can feel it in the gas pedal when the car is doing this I tried replacing the throttle body sensor but it still does it I also was told it was the Idle error sensor. So instead of spending the unecessary money again I thought I would go online and see if anyone could help me with this problem.

egr vavle?