I'm doing some work on a friends 1996 850R wagon and after some extensive repairs: timing belt, water pump, oil trap, soaked the PTC in brake fluid, cooling system flush, new thermostat, and spark plugs the car will struggle to idle when I first start it up. If I give it a little gas it runs fine but as soon as I take my foot off the pedal the RPM's drop and the engine shakes. As the vehicle warms up the RPM's will sometimes jump to 2000 and than full back below 1000 causing the car to shake. It almost seems like it's running on four cylinders yet no CEL. Once the vehicle has reached normal operating temperature it appears to run fine it's just the initial five to ten minutes it's very rough. I'm wondering would a clogged fuel filter or just bad fuel make it run rough when it was cold? Driving it on the road I don't notice it so much but sitting in my driveway in park it is very noticeable even the exhaust sputters as it struggles to idle.

 

Have you checked all the Vac lines? And the idle control valve? Hopefully you didn't get timing off by 1 or 2 teeth (check the timing marks again)?

 

Yes, my biggest fear was the engine timing. I checked it again after the car had been running for several minutes and everything lined up correctly. When I did the oil trap I did not replace all of the vacuum lines (too costly). I had to replace the vacuum elbow at the PTC which had broken into pieces. I also took the air pipe off of the turbo and removed the PTC so I could soak it in brake fluid and I cleaned the large black hose. I still see some smoke coming out of the dipstick at idle. I have an extra IAC so I might try swapping that to see if that makes any difference. I have read that the wrong spark plugs can cause a rough cold idle so I might try putting in the original plugs again. Thanks RSPI.

 

I found the problem. It was a disconnected vacuum line. I forgot to connect the one that is on the front of the intake manifold that goes to that solenoid valve next to the fan. I was amazed how well the car ran once I had hooked that hose back up. It also appears that there is no longer any smoke coming from the oil dipstick.