BroncoII4x4.com

One of the reasons I parked the Bronco was the fuel mileage. When I start it up it idles a little high but all plugs are firing. When the idle starts to drop it runs pretty rough, sometimes stalling. Even after it has warmed up it shakes all over the place. Plus I can smell it is running rich. This has happened before and the mechanic said all he did was clean out the vac. lines. I tried it on my own and it still runs the same. Any ideas.

Fuel pressure regulator. It probably has a pin hole in the diaphragm allowing fuel to get in the vacuum lines. Pull the vac line off the Fuel Pressure Regulator. Look and smell for the presence of fuel in the vacuum lines. If ya got fuel in the lines replace the regulator.

I pulled the line off of the regulator and checked it for the presence of fuel. It seemed a little dirty but no gas smell. While doing this I noticed no change in the engines behavior. Could a failed MAP sensor cause the motor to run rich? I was also told to suspect the TPS. Wouldn't the Check Engine light come on if either one failed?

not necessarily, my bronco II has never had a light come on unless it was HOT or low on oil......... of course i think about ahlf my dash gave out long ago...........LOL.......... MAP sensor can absolutelt casue it, and check the IAC, it should alter after it warms up, (CLOSE) to reduce the amount of fuel allowed into throttle body........by the way teh IAC is attached to the side of the throttle body about 2 inches from where the input end of it is by the breather hose, will be on driver side....... its a notorious booger..... and an oxygen sensor can cause a truck to run rich also

Paul wrote:not necessarily, my bronco II has never had a light come on unless it was HOT or low on oil......... of course i think about ahlf my dash gave out long ago...........LOL.......... MAP sensor can absolutelt casue it, and check the IAC, it should alter after it warms up, (CLOSE) to reduce the amount of fuel allowed into throttle body........by the way teh IAC is attached to the side of the throttle body about 2 inches from where the input end of it is by the breather hose, will be on driver side....... its a notorious booger..... and an oxygen sensor can cause a truck to run rich also

the TB does not get fuel
the IAC is not attached to the TB
the IAC is not on the drivers side
the IAC does not control fuel

Umm. What is an IAC?

idle air control

Just went to look. Hey! I have one of those! I have a love/hate relationship with modern technology. I love how durable engines have become but hate the fact that when something does go it takes a little time to sort it out. Can't just check if there is spark at the plugs and fuel in the carb. Oh well.