My 97 960 threw the timing belt off when the pulley bearings went south, and bending 2 intake valves. Lucky for me it happened while starting the car and not on the highway. I tore it down, replaced the 2 valves, cleaned the others, lapped the seats, installed new seals, gaskets, etc. Put it all together and it runs like crap. Not bad above about 2000 rpm, but really rough at idle. Compression is good, fire at the new plugs,correct cam timing and firing order, and all sensors are connected. Will run a little faster with MAF unhooked, but still very rough. Exhaust smell very strong. I got all the vacuum hoses hooked up, can't see anything I missed, and I have not been able to find any websites with info on checking the codes for this year and model. Can anyone help?

 

The 6 cylinder will seem to run fine on 5 cylinders at about 2000 rpms or more. So could you have crossed a couple coils? Did any of the wires leading to the coils break?

Another item, is the little hose connected to the idle speed motor?

Did you forget a ground wire? There is one on the driverside engine mount bracket that eluded me on my first head repair.

If you have good compression, then it must be missing spark, or a vacuum leak.

DanR '94 964 354,000 miles (120,000 on the new engine)

 

I know the coils are correct and in order (followed the wire colors), small hose on idle motor is on, do not see a ground wire near motor mount. What or where did it connect to? I read a post about the intake needing to be grounded, and since I couldn't find one I hooked up a temporary one but it didn't improve the idle.

 

The intake does not have to be grounded, anything attached to it will be grounded with it's own wire, but those wires, 02 sensor heater, power stages ground, MAF come from the wire at the engine mount bracket, look for a black plastic wire chase, there is a small bolt that holds that chase channel to the bracket, while that bolt passes thru the bracket and can be tightened by the threads in the bracket itself, there is also a ground tang and a nut to go on the end of that bolt.

What can happen is the ground tang is touching the bracket but not securely.


Can you isolate the miss? Is it running on three cylinders?

Can you check for any intake manifold leaks?

What about the air valve at the bottom of the air filter housing, the one that directs air flow from the exhaust manifold when first started cold, that valve has been known to stick and permanently allow hot air to be drawn in and effect the MAF sensor function.

DanR

 

Hi Dan. Finally found the ground you were talking about. It is ok, but what a pain to find. Modified my air cleaner housing last year to draw only fresh air, wasn't sure it worked correctly and I live in the south so it's not an issue. I installed a new intake gasket, new injector seals, and new clamps on the intake collars when I put it back together. Do you know any tricks to check for leaks on the intake side? Shade tree

 

I have used propane and a small hose, do this outside though.

Attach a short hose to the end of a propane torch, turn on the gas (don't light it) and then follow around the intake areas, the gas gets drawn into the leak and the engine speed will change, sometimes it will even out the idle.
Disconnect the air ducting from the air filter box, but leave the MAF connected, then let some propane enter the engine thru the air duct, if there is a vacuum leak or (unmeasured air), the engine idle should change too. So that leaves a leak somewhere, a hose, a fitting, a gasket leak.
On my engine, the bolts holes that held the intake to the head were stripped out, the bolts would take the torque required and the engine ran fine for several hours but then would get rough and eventually throw a engine code. Repairing the bolt holes was required.


But be for you do that, could your idle speed motor be stuck? When you have it unattached, hold it in your hand and twist your wrist sharply back and forth, the valve portion should make a clicking sound as the valve internally hits the valve stops. Could there be something wrong with the throttle position sensor.

Are there any codes?


DanR '964 355,000 miles (121,000 on the new engine)

 

Pull engine codes. Do you have a CEL? It will tell you if you have a mis-fire.