Ok guys and gals I have an issue I can't find a solution to on this website. I have a 2002 Ranger 3.0 that idles rough only after its warmed up to operating temperature and the RPM's have dropped to idle speed, which settles at around 650 or 700 on my gauge. I've replaced and taken care of all the usual suspects that cause rough idle, MAF, IAC, PVC VALVE, PLUGS & WIRES, CAM SENSOR. When I unplug the IAC the idle drops like it should so there are no vacuum leaks from what I've read on here. I changed the thermostat and coolant temp gauge.

I suspected the exhaust system might have something to do with it because it was a little loud, and it seems like the whole truck shakes, not just the engine. so I took off the cat converter and found out it was hollowed out all the way, and I read on here that it could cause even more back pressure, or gases coming back to the engine. So I've even replaced the catalytic converter myself. The truck is quieter, but the shaking is still there. I now suspect the Muffler is clogged a little but I'm not sure. There is some flow out the tailpipe but it seems a little muted but I'm not sure.

My questions is will a semi clogged Muffler prevent the exhaust flow enough to cause enough backpressure to make the engine shake? Has anyone had the same problem?

Also, I have adjusted the idle screw to increase the idle to around 750 or 800 with the IAC off, unplugged battery and restarted. I did this to see if it would make the shaking go away. It helped a little but not much. Is there any side effects of setting the idle that high? Can the throttle position sensor voltage being out of whack cause the engine shaking during idle? THE TRUCK RUNS GREAT WHILE ITS MOVING AT ALL SPEEDS. Is that because there's enough pressure to move the exhaust out and prevent backpressure from the maybe semi clogged Muffler maybe?

Any thoughts would be appreciated.

 

That shaking is probably a misfire. If your cat was empty you must have a check engine light on. The codes will point you and people on here towards the problem.

 

I have fixed all the codes and replaced the catalytic converter and all O2 sensors. I haven't had any codes now for a while. I just adjusted the voltage on the throttle position sensor to around .90, and its idling at 750 while in drive and 800 when I put it in park, and it seems the shaking smoothed out a little, but its still not right. It seems like the longer I sit still in idle the worse it wants to shake. Its seems like its a little smoother in neutral and park, but barely. If I had a misfire wouldn't I get a code?

 

a no code misfire is a thing. Especially with ford. The computer detects a misfire as a change in the rotating speed of the crankshaft. So, a dead miss in one cylinder ( no combustion at all) will not push down on the piston at all. But if there is still some combustion happening it still pushes down on the piston but the loss in speed is not as great. The computer has a limit set of how much this speed can change before it counts it as a miss.the rhythmic change in speed is the shake your feeling.

You opened a bag of worms messing with that screw.
the tps should read around .53 closed and 1.27 wide open. Set it back to factory. Then, figure out what is actually wrong.

The engine needs spark, fuel, and compression. You replaced coil, plugs,wires.. all motorcraft I hope. Probably would've taken care of a spark issue assuming nothing was defective out of the box. Next up fuel pressure test. Compression test.
happy hunting