I'm new at this so I hope I can provide enough info for an educated guess. full size '90 bronco 302. It starts fine then produces a rough idle, almost dies then recovers without any help on my part, this repeats for a few minutes, any time of day, put into drive/reverse and it wants to quit and sometimes it does. Driving down the road it stalls out, sometimes dies (put in park and restarts just fine), and sometimes recovers and then normal. It shifts a little hard as well. Does the tranny have anything to do with the engine acting like this? I am at the end of the rope as far as what I can think of and the end of the money tree. Here is what I have checked (replaced mainly): fuel pump and wiring, fuel filter, egr valve, egr positioning sensor, ignition module on distributor, ignition switch on steering column, stator/pickup coil in distributor, grounds are all new and good on engine, fuel pump, frame, body. rotor and cap are good, fairly new plugs. I'm checking the vacuum lines tonight, other than that ? I appreciate all the wisdom and experience you all share.

 

I'm having the same problems as you and I also can't seem to find what's making it do this. I do keep finding a rubber hose on the back of the engine that comes off the smog pump and connects to some type of valve -- it keeps blowing off. I'm starting to think this is the problem because after I put it back on and drove it, it didn't buck and stall.

This hose connects to what looks like some type of vacuum valve? The line comes off the smog pump on the passengers side, goes around the back of the engine, hooks to this valve that is attached to a pipe that extends across the back of the heads. I'm not exactly sure what this actually does as I'm still looking through a Haynes book.

I've replaced the inline fuel pump, the fuel pump module, EGR valve, EGR position sensor, spark plugs and spark plug wires. When idling and driving, I can still feel a miss. It will run for a while, then a few miles down the road it will cut totally out, buck, stumble, miss, then quit. It will start back up and do the same until I get it home and it cools off.

If you find out what is making it do this, please tell me!

 

If you want to see the pipe/valve I'm talking about, get a haynes manual for 1980-1996 For Pick-up and Bronco. Look on page 6-2 illustration 2.3b. Note it's on the rear of the engine.

 

hey cnady here,
did you ever find out what the problem was with your engine (back from a June post, engine quits or stalls)? I hope you had better luck than myself. Those valves you were talking about are check valves with the vacuum and exhaust. That's as much as I know about them, but mine checked out O.K. checked them with a friend a vacuum pump. I've still got the trouble and keep testing sensors and such. I've cleaned all of them and put some new gaskets on the intake manifold as well as the previous stuff I've done. I think I'm headed to the dealership and spread some $ their way

 

Sounds like some sort of vac leak. Get a can of starting fluid and start spraying vac hoses and anywhere there might be an intake leak. Make sure the engine is idling. If you hear the engine rev up when spraying it, you've found your vac. leak. Also do those engines have mass air or MAP sensors? Could be either one of those.

 

Thanks for the reply. It has a MAP sensor which I'm going to check tonite. A while back- 3 months or so- I did try the starting fluid around the vacuum ports & hoses to no avail, but it certainly wouldn't hurt to try again. Does anyone know where to find a vacuum diagram for a '90 302 efi.? The one under the hood is non-existent. Thanks again

 

My 89 F150 with 302 and EFI did that quite often until a guy told me what was wrong. It was low on water in the radiator and the sensors couldn't tell the correct engine temp, so the computer kept f*(k1ng with the choke.