FerrariF1fan

I have a 1986 Mustang LX with 5.0 HO. Recently, the engine began running terrible. At city and highway speeds, the engine hesitates and sputters and sometimes makes popping noises in the muffler. When it's acting up and I give it full throttle, it goes flat and acts like it's not getting enough fuel. Right now, when I start it, it idles up, the tries to idle down to normal warmup idle, then starts idling rougher and rougher until it dies. I can keep it running if I give it throttle when it starts to die. Once it's warmed up, it will keep itself running. But when I try to drive it, it hesitates and bucks a bit. I'm really afraid it's going to leave me stranded somewhere.

At first, I thought it was a fuel delivery problem. I put a fuel pressure gauge on it and had a steady 30 psi of pressure that increased to 40 psi during acceleration. I even ran the car on the road with the gauge taped to the windshield. When it did began running rough, the fuel pressure remained perfectly steady at 30 psi. So, I surmised that I did not have a fuel pump going out.

I ran the KOEO and KOER tests and did pull a few codes. I got a 31 on KOEO and 33, 92 and 12 with KOER. I pulled the EGR valve off. It is working fine and holding a vacuum. I also used an ohm meter to test the EGR position sensor while pulling various levels of vacuum on the EGR valve. It got readings that varied based on the position of the diaphram in the EGR valve, so the position sensor appears to be working fine. Then I tested the hoses running to the EGR valve and back to the original vacuum fitting on the intake manifold. All hoses tested out fine with no leaks. So even though I'm getting an EGR code, all of the components and vacuum lines seem fine.

As far as the 12 code which is the idle speed control motor not controlling the idle properly, I've also removed it and cleaned it. I know the idle motor is operational because at startup the engine revs up then starts to idle down. I think I got the code because the engine died while I was trying to obtain the KOER codes.

I'm really perplexed on this and I need to get the engine running good again. I'm wondering if I may have a problem with one or both O2 sensors, the water temp sensor or the MAP sensor. Anyone out there had similar problems and determine what the problem was. Or does anyone care to venture a guess based on my description of the problem? All help would be greatly appreciated.

Grace and peace,

Robert[/align]

Blckstng93

Not sure about the 86 but ill give it a shot. Im still learning this stuff to.

Code 31 - check the EVR solenoid on the passenger side strut tower. Has 2 vac lines, one to the EGR and another to a vac source, not sure where. Did you check that to?

Code 33 - EGR valve not opening or not closing completely. Just because you get readings on something doesnt mean its good. Cleaning the EGR may help, they can get pretty dirty after a while and get hung up on bad carbon buildup. Carb cleaner and a stiff brush work good.

Code 92 - O2 sensor is reading rich. Left side.

Code 12 - rpm unable to reach upper test limit. You cleaned the idle motor but maybe it isnt opening far enough?

Did you run the test with a warm or cold engine? Should be at operating temp. Check the inside of the intake behind the throttle body, they can get pretty dirty.

Vader87

I dont know about all the codes, but I have had the same problem on many of my stangs, & usually it turned out being the tp sensor. Maybe you have a friend that has a 86-93 stang. See if you can borrow his/her tp sensor, a quick way to find out. Good luck!

86 5.0L

after the IAC, I would check the TPS, im inbetween those 2 right now....

aceofSpades

possible detonation?
stop using cheap gas