2.9 trouble

[84ranger]

my 88 BII idles a little rough and bogs out when I punch the gas but only for a couple seconds then it takes off I was wpndering if anyone could help me out.

[BigBlackRanger]

Well, start by cleaning and resetting the IAC motor, then check the plugs, cap, rotor, wires, etc for wear and/or damage. Do a through inspection of the wiring, make sure you don't have any loose grounds or plugs. You may want to remove your throttle body and clean that, too. I did this and it really helped in terms of idle quality. Also, check your timing.

[BigMoose]

i've been having the exact same problem with mine too. where is the IAC? is it that long tube on the upper intake manifold?

[BigBlackRanger]

The IAC is located on the passenger's side upper intake manifold, about 1/3 of the way back. It has an electrical connector on it and is plumbed directly into the manifold.

[BigMoose]

Thats what i thought, i changed that and i still have the same problem. in the chiltons it calls it the air bypass valve, i didn't know they were the same thing.

[CowboysBronco2]

84ranger, here's a few items to check...

If the IAC (Idle Air Control motor) was at fault, most likely you would have a "loping" idle (up and down)....

Obviously you would want to check the ignition (cap, rotor, wires, coil connections) as stated previously...

Timing will not change unless you remove the distributor for any reason. If this has been done, make sure to set base timing the way that the emissions tag in the engine compartment tells you..... Warm up the truck, shut it off. Disconnect the inline SPOUT (SPark OUT) connector (located on the passanger side of the engine, right between the intake and the valve cover). Restart the engine and ensure that timing is 10 deg. BTD (Before Top Dead center). Shut engine off and reconnect SPOUT.

I seriously doubt that this may be a problem, however.

I would go to the local auto parts store and check fuel pressure. Just because there are 2 fuel pumps on the bronco doesn't mean that they can't go out. In fact, with just the secondary pump running (and not the one in the tank), the truck will actually "buck" when driving. (No pun intended. Bucking bronco's, get it? ha ha. :) )

Also, the ACT (Air Charge Temperature sensor) may be bad and gummed up (located on the passanger side of the upper intake, screwed into the side).

Also the 02 sensor may need replacing. I would recommend testing it to ensure that the crosscounts (the times that the voltage changes from rich to lean (low voltage, high voltage)) are okay. Crosscounts for a good O2 will be 10 times. If your O2 sensor is "lazy", then there is a chance that this may be your problem.

Also, but not likely, the TPS (Throttle Position Sensor) may be bad. Again, probe with a volt meter. The voltage should steadily increase as you open up the throttle (don't have the engine running when you do it). This is refered to as KOEO (Key On, Engine Off).

If you need more help or ideas, let me know. My fingers are getting tired. :) LOL