86 Bronco Plenum

[itsrickfromfl]

Has anyone had to remove the plenum and have it vatted/cleaned, to get proper air/fuel mixture? I have been told it is very common on the late 85/86 302 fuel injected engines to have a carbon buildup inside the plenum, and that the computer constantly is fighting to get proper air flow.

My 86 Bronco (302, automatic transmission, with early fuel injection) has trouble idling smoothly, especially in gear at traffic lights. It will idle around 600 RPM's in gear, and suddenly act like the engine is going to quit. Sometimes it does, but will restart immediately. To get around this, I have been taking it out of gear at red lights.

I have replaced both fuel pumps. I purchased a code reader, and have replaced the ignition control module, fuel pressure regulator, MAP sensor, fuel filter, plugs, rotor and cap. The catalytic converter was removed from the truck prior to me getting it, but the air pump is still connected. The truck is running much better, but this idle problem needs attention; not to mention I am also looking to improve gas milage.

It's been suggested that I remove the air pump, take off the hoses and place thermistor plugs in the back of the heads, and remove the plenum and egr for cleaning. Some have suggested sandblasting the plenum, and one person suggested I take it to a transmission shop and have it vatted.

My other truck is down right now...a Texaco Express **** didn't replace the top differential plug, and the rear end burned out. I am driving the Bronco daily, and have thought about buying another plenum, having it cleaned out, and doing a swap, so my down time is minimal. If this will fix my problem, what year range are the plenums interchangable?

Any thoughts or suggestions would be most appreciated. I love this truck, and want to make it run like it once did!

 

[Seabronc]

The carbon build up comes from the EGR valve. If that plenum has never been off, you may find the EGR port clogged and the EGR stuck open due to carbon deposits. The EGR stuck open at idle will cause the engine to run like crap. You may need to change the EGR and clean the port. Running it through a transmission case washing machine (vatted) might be a good idea.

Good luck,

>-

 

[Roadkill]

I think Seabronc is right. I have seen stuck open EGR valve cause those same symptoms in several vehicles (Ford, Chevy, AMC, and even a newer Mitsubishi) runs fine going down the highway, but won't idle worth a damn.

Edit:

By the way, Welcome to BroncoZone! >

 

[Big_Ford_POS]

check your vaccum lines before you waste too much money, or if your smart replace them all ( one at a time so you don't get mixed up) buy a roll of line the autozone. Like 1/4 & 5/16 size I'm not sure. But it two different sizes.

 

[itsrickfromfl]

Thanks for the great suggestions! I have been planning to replace the vacumn lines...there's been so much to do, I just hadn't gotten to it. I will take off the EGR and clean it, and see how that does. Again, thanks for the help, and the warm welcome!