Hello again, without writing a book, I am still having problems with my 88 351W that I recently rebuilt. It runs very rich when cold, and after coming up to temperature, it runs good for a while. Then after a while it starts idling erratic and very high. It will not straighten up til you shut it off for a while and let it cool down. Then it will run fine again for a while untill something warms up and then idles very high again.
I have changed the fuel pressure regulator, ignition module, blocked off the EGR, computer, air temperature sensor in intake, water temperature sensor, MAP sensor, checked for vacuum leaks, and removed all injectors and had them professionally cleaned. Also removed all vacuum lines (except fuel pressure Reg line and MAP sensor). I also have unplugged the O2 sensor to see if that made any difference and re-plugged. It does make a difference, but not a lot. The coil is new since rebuild, as are plugs, wires, bug, and cap. The only other thing I can think to mention is that I have removed all smog pump and plumbing. All vacuum solenoids are still hooked up to the electrical, but no vacuum. Tube coming from cat is plugged, holes in back of heads are plugged. New PCV valve and hoses to it. So far nothing I have done has had much of an effect, if any, on it at all. I am pretty much out of ideas and I need help. I appreciate any and all ideas and also the help that others have given me so far.

Jim

 

I'm wondering if you have a bad pick-up coil in the distributor. These can cause some wierd problems.

 

The distributor has a module on the outside (which has been replaced). Is this a magnetic pickup? Is it a dealer item? Also I am wondering if the coil itself is bad. It is new, but it isn't totally out of the question to get a bad one.

 

The pick-up coil is inside the dizzy. Yes it is the magnetic pick-up. It can be bought at any parts store.

 

Finally found the problem. Turned out the throttle positioning sensor was putting too much voltage to the computer. Basically like the throttle was 1/3 open when completely closed. Runs absolutely great now. Thanks for everyone's help and thought.

Jim

 

Glad you got it figured out