Guys,

I need some help and advice. I have a 192,000 mile '88 with a 300 six in it. When you start it cold it starts and runs fine. Problem is that when the computer tries to bring it down to curb idle from fast idle it starts to gallop. It seems to me like it's trying to curb idle too soon before it is warm enough. It will try to curb idle and try to stall like the mix is too lean. Then the computer catches it, runs it up to 1800 rpm and tries to idle it back again. This goes on until it finally stalls or gets warm enough to run on the mix. After it is warm enough it sits there and idles just like nothing is wrong.

I have replaceced plugs, wires, cap, rotor, and air filter they were all just short of 60k interval on them. All Motorcraft. I have looked all over for this thing to have a vacuum leak and found nothing. It's pulling 19.5 inches. I did find and replace an exhaust/intake manifold gasket. The exhaust side was burned out on #5. I thought it might be leaking into #5 or #6 intake but could not really see where that part of the gasket had gone bad yet. I cleaned the air temp sensor in the intake while I was there as well. It was built up with oil sludge from the pcv system. That oil didn't make any sence to me either. Ran an ohms test on the sensor and it was within the range in the Haynes book.

This is where I stand right now and I am just about ready to admit defeat.

Any help anyone?

 

Run your scans for error codes.check the seal grommet the Pcv mounts with for leakage bypassing around the valve & the valve function itself. might try cleaning the Idle speed Control Valve & see if the resistance is in range (7-13 ohms).

 

Those old six cylinders were good for dirtying up the fuel injectors pretty regularly. We've had to clean them several times at the shop before they're running right. Our method involves running the fuel system from a self contained unit with the fuel and solvent in a separate container with the fuel lines blocked off on the rail. Engine runs off the can with air pressure. You could try running a few tanks of injector cleaner through it and see what happens.

 

ymenski, I will double check the PCV and check the ohms on the idle air controll. I did clean it first thing, wich I forgot to mention. I have always had trouble with this truck since brand new. Clean the IAC every 15 to 20K and she's fine for another go. It hasn't set any codes.


bigbronc, I have 192,000 on the old girl and have never done one thing to the injectors other than a can of cleaner here and there. Any suggestions on the best injector cleaner. I'm partial to the stuff made by PB Blaster.

 

Only thing I've ever used is the motorcraft concentrated cleaner from work. Like I said, this is used mixed with gas inside a seperate container with the fuel lines blocked off and air pressure applied.