My 93 F150 302 has an issue with a slightly rough idle, a slight hesitation when pressing the gas, and a surging when at a constant throttle position. I've replaced the entire ignition system, including the distributor and verified the plug wire routing, replaced the TPS and EGR position sensor. EGR works properly. This problem is only in closed loop. While the engine is cold everything seems to work fine. I can open the throttle a bit, say 1500, and there's a surge, or maybe you could call it an "anti-surge" where the rpms will drop a bit and engine roughens up a bit, then it goes back up and smooths out, then cycles back down. Seems to be more prominant when under load like when going up a hill at around 40 MPH. Vacuum system is tight, zero leaks. You can even hear air ruch in to the vacuum line to the brake booster when it's disconnected after shutting down the engine. I cleaned the throttle body and replaced the TB gasket. Checked the fuel pressure and it's 35lbs with the regulator vacuum line connected and 45 the line disconnected. Same on both tanks. New fuel filter as well. MAP sensor seems to be working. No MAF sensor for this truck. I'm totally out of ideas.
Friday, June 10th, 2011 AT 6:40 PM