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.
On brake booster where hose goes to plastic valve that sticks into booster. Remove should be able to blow into but NOT suck
Has truck been checked for trouble codes? Will MAP sensor hold vacuum?
June, 10, 2011 AT 7:58 PM
Haven't checked to see if the MAP will hold a vacuum yet but will do that right now. I'll give the booster valve a check as well.
June, 10, 2011 AT 8:07 PM
OK, booster valve works as advertised and MAP will hold a vacuum. Also, no codes.
June, 10, 2011 AT 8:35 PM
Did you get a code 11 or 111?
June, 10, 2011 AT 8:55 PM
I checked the codes a few weeks ago and the only abnormal code I got was for the EGR position sensor which I then replaced and the code cleared. If I recall, I did get a 111 code.
June, 10, 2011 AT 9:10 PM
Mind checking again we need a clue
June, 10, 2011 AT 10:04 PM
Good to go. I'll check it again and get back with you in a couple hours.
June, 11, 2011 AT 1:02 AM
Yep, got a 111.
June, 11, 2011 AT 6:07 PM
Well out of ideas myself without being there. Really fits vacuum leak try removing EGR vacuum see if that helps. Have gone around intake spraying Carb cleaner to find leak?
June, 12, 2011 AT 5:45 PM
Sure have. No indication of a leak. I think I've tried the EGR vacuum but I'll try that again to make sure. Any idea of what sensors come in to play when the computer goes in to closed loop? Thanks for your help!