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'88 GT automatic. Runs good at idle when cold but once it warms up it surges. Meaning it runs good then drops out almost to the point of dieing then back to idle, and repeat...Does it with the electric fan on or off. When it was really hot last week it did it almost immediately after start up. Don't notice it when cruising until you come to a stop and have to keep foot on gas. Thought it might be TPS and picked up a new one, but same condition. Anyone else experienced this and cured it without replacing every sensor in the process. Could ignition module do this without total failure? Thanks for the help.
Try cleaning the IAC valve with carb cleaner. Next clean the EGR valve up near the throttle body. Both of these carbon up and need to be clean and free. Cheap to do in thirty minutes.
IAC stands for Idle Air Control valve which controls the idle speed and steps up for A/C operation. It attaches to the throttle body and acts like a by pass around the throttle plate. I clean mine once a year.
Removed and cleaned the IAC. It moved freely and the Stang dies when unplugged, so assume it's working properly. Also removed the EGR valve and guess what? it was stuck and had crud built up around it. Cleaned it and broke a loose the stuck valve and reinstalled. Sympton still there. When it starts the surging or loping, the RPM's are varying from 600-900. Now I'm thinking clogged PCV screen and valve, and just noticed the are the original wires with 1988 on them!
I would do a good tune up with plugs, wires, rotor, cap, fuel filter. And I would then reset the computer with a battery disconnect which may help idle control. All of this for not much money.
My 87 was doing the same thing until I got the spacer plate for the IAC and also reset base idle and adjusted T.P.S, voltage was at about .85v, so I adjusted it to .97v and it corrected the problem. You may also want to check for a vacuum leak.
You're not the only one. I just replaced spark plugs, cap, rotor, and wires, and I have a horrible little secret I want to share. Yes, I did the PVC...BUT DON'T BE FOOLED. Under the PCV grommet is a horrible contraption called a PCV SCREEN, which is like a sink strainer. This nasty thing becomes clogged with oil. Once it does, your oil will force its way out of the valve covers and main seal. It took me two hours to remove this thing and I had to lay a long board on top of the plenum and lay on the engine to "chisel" it out. A replacement is made by Dorman: I got it at ADVANCED AUTO PARTS. I also replaced the downstream CATALYTIC CONVERTER. Oh, and...this is a must...check the vacuum hose that leads to the MAP SENSOR and you will have to pull the plenum to change it. IT IS PROBABLY ROTTEN. More funzies...the plastic vacuum hoses can shrink in diameter and become so brittle they crumble in your hands. I spent three grAND SO FAR and nothing has worked.
