91 Taurus SHO Shaking/Electrical Problems?

To start off, I'll admit that im not a grease monkey, but I know my way around the basic systems of cars. My dad is a journeyman mechanic, but he's been in California lately and hasn't had the opportunity to experience what it's doing first-hand.

What happens is that the car will randomly start violently shaking (to the point where I'm afraid it's going to start breaking stuff). So far I haven't really been able to notice anything specific that causes it. If you put in the clutch in the shaking goes away, but the idle will flutter back and forth about 100 RPM, cycling about 4-5 times per second. What really makes it interesting is that when I turn off the ignition and try to start it back up, for a few minutes the car will either crank but not start or randomly lock up (like the battery is dead) and after it finally starts again I don't have a tachometer. I tried cleaning the ICV to no avail. Dad says it might be timing, but what I don't get is how it can cause the starter lockup or the tach. Anyone heard of anything like this?

There's another problem that I'm having, but it's probably not related because it just recently started. The car runs rough at idle and particulary when you give it a moderate amount of gas at low RPM (like taking off or right after shifting) it backfires (not a bang, but more of a soft puff). I thought one of the spark plugs might be bad, so I opened up the front 3 plugs and all of them had a lot of oil in them (one plug was completely submerged), but from what I've heard that isn't too uncommon. I test the resistance on them with a multimeter and they came back fine, so I started it up and disconnected the spark plugs one at a time and all of them made it worse. It also seems to be lacking a little power until you get to about 3-4k RPM where it no longer backfires or runs rough.

If anyone can give me some ideas, that would be awesome.

Welcome to the forum!

True, leaking spark plug well seals is not uncommon, but you still don't want the plugs submerged in oil like that, it will cause misfires.

I was going to suggest that you check for oil on the plugs until I read about the tachometer not displaying at times. That leads me to suspect that you have a bad ignition control module. Your symptoms are very characteristic of bad modules for Fords from the mid-80's, it's not quite as common on the SHO. Unfortunately, from what I've heard the module on the SHO was only used on two engines, the SHO V6 and the supercharged V6 of the Thunderbird SuperCoupe. I've heard that they are not very easy to come by (which is why I purchased a used spare from eBay several years ago when I still had my '93 SHO).

You should also do a thorough visual inspection under the hood to make sure the vacuum lines are all in good shape.

-Rod

Makes sense. My CE light had actually been coming up after a few minutes on the road, but since it doesn't have OBD I had to take it to a mechanic that had the old school reader and it came up with something cryptic along the lines of O2 sensor not switching and something about the neutral safety switch I think it was. One thing I forgot to mention is that the trouble starting and the tach used to only be after the shaking and fluttering idle happened and I turned off the engine, but now it will do it when the engine is cold too. I tried cleaning out the front spark plugs as best I could, but it seems pretty much impossible to get to the rear ones without dropping the cradle, which is why I couldn't clean or test them. I actually got a second SHO while I was out in California once that had a newly rebuilt engine, but the transmission went out after not even a month. Now the transmission on the old one is starting to show its age, so we're trying to find a tranny so we can just swap the whole thing at once.

Thanks!

The rear plugs and valve cover gaskets are easy to get to with the upper intake manifold runners removed, which actually is no where near as bad to do as it looks like it would be. The most difficult part was removing the Idle Air Control (IAC) without dropping the cap head screws. I don't recall exactly why the IAC had to come off to remove the intake runners, I just remember that it did.

-Rod

Sorry about the lack of response, but I've been really busy lately. I'm having trouble finding info on how to get to the ICM, probably because it appears to be referred to as several different names (ECM, ECU, i think DIS was one). Is it going to be behind the glove box?

On my 1993 it was behind the glovebox. However, since the body style changed in 1992, I'm not sure the location will be behind the glovebox in the 1991 as well. You can check the firewall under the hood to see if the large rectangular multipin connector appears to go to the glovebox area before dropping the glovebox door.

-Rod