Rough Idle
 

87 944s

Car Starts Good Runs Good At Higher Rpms
But Getting The Rpms Up Is Not Easy

Computer Went Bad I Got It Replaced

Has New Rotor & Cap And Wires.

The O2 Senor Drains The Battery

Any Help Or Suggestions Will Be Greatly Appreciated

I would start with checking for vacuum leaks. With the car being 20 years old, any original vacuum lines are bound to be leaking.

I replaced all mine (little by little) and my idling improved significantly. I started with all the rubber hoses, then the intake boot, then the cloth covered hoses to the cannister, then the hard plastic lines, and lastly, the goofy hose under the manifold that goes to the idle control valve/oil vapor seperator.

At each stage of changing out the hoses (which took me about 6 months), my idle improved. These cars are critically dependant on vaccum - any leaks will cause the car to run improperly as this is unmeasured air entering the system and the computer will not compensate with more fuel. The only air that should be entered into the system is thru the air-flow-meter which the computer measures and adjusts accordingly.

I also changed my oxygen sensor and cleaned the idle control valve.

My car used to vibrate and idle up & down but is now smooth.

Vern

p.s. while you are at it, you may want to clean up all grounding points. My car only has 29k miles and was stored for 1/2 of it's life and it still had coroded ground points on the engine and the vacuum lines leaked eventhough they looked brand new.

Allen2145:

First, welcome to the Pelican boards!

Second, as Tidybuoy said above check all the vacuum hoses to ensure they are not leaking.

Third, did you happen to do a complete service or rather tune-up? Just wondering if you had a chance to also change out the fuel filter if that hasn't been done and whether or not the spark plugs are new. I would check all the basics such as spark, fuel and compression for starters.

Lastly, because it is Winter and depending on where you are located, you might need to change your oil. Here in Eastern Washington, it get very cold at times, so I run Mobil 1 Syn 5W-30 during the Winter months and Mobil 1 Syn 15W-50 during the late Spring, Summer and early Fall.

Hope this helps and do let us all know the progress you are making.

Good luck!

rough idle
 

In Looking For Vacuum Leak I Knocked And Injector Plug Off
It Made No Difference In The Way The Car Ran It May Be The Problem
I Hope But As Suggested I Will Replace Vacuum Lines


LOTS OF THANKS

The wiring harness for the injectors does break often. You can buy a noid light to plug into the harness and see if that is the problem. There is a splice in the harness somewhere that corrodes (IIRC) and that may be your problem. Buy the light and test that...I don't think it's but a few dollars.

Can you please expand on this statement??

Like Tidybouy (and a number of us, I bet), my idle steadily improved as I replaced vaccum lines and cleaned grounds. Plugs and wires, cap and rotor also settled it down a bit more for me. Motor mounts were a huge factor. Also, a new O2 helped a whole lot when transitioning off-throttle to idle.

And, especially since its an S, I'd make sure the ISV if working right (idle at ~850rpm, even with AC on, a tad over ~1000rpm when real cold, rpms don't plummet and nearly stall on throttle off).

I also agree with onZedge. The O2 sensor helps set the fuel mixture...if it's shorted, then it can't possibly be working correctly which means the fuel mixture is off. Definitely one problem..not sure if that is the only one or not though.