Help. I am so frustrated with this car. I can't get it to idle well. I replaced the fuel filter, spark plugs and wires, fuel injector seals an O-rings, distributor cap and rotor, thermovaccum valve, Air valve, set the timing to TDC according to my maintenance manual checked all vaccum lines for leaks. The car runs fine at higher rpms, at idle~800 rpm's when warm it shudders lightly in P or N. At a stoplight in D it shudders so bad it almost stalls. If I set the timing to 20 degrees ATDC it idles faster but not smoother. I need to take this car on a trip soon and have to get it running better. any suggestions?