2.9 3000rpm between shifts

[WillinHiFi]

My 1989 Bronco ii 5Speed will jump up to 3000rpm when i shift gears and it will stay that high until you go under 25mph. Then it will return to 1000rpm idle. I have a KOEO code of 41 which is O2 stuck lean. Ive found one vacuum leak were the plenum meets the lower intake. I was able to get the rpm to raise with propane around the front two intake runners. i cant get it to do it again and im at a loss.

 

[RonD]

Welcome to TRS

First check the throttle return spring, on the throttle linkage on upper intake, remove cover, and with engine off manually open throttle and let it snap closed with spring pressure, if spring breaks or gets weak then throttle will hang open because of air flow.
Now start engine, watch out for FAN, and do the same test, see if air flow makes it hang open.


Fuel injected engines can't use an idle screw so they use an IAC(idle air control) Valve to control idle RPMs.

On the side of the upper intake near the throttle you will see a "can" with 2 wires connected, that is the IAC Valve.
This Valve opens and lets air in to increase engine RPMs, so it is like a Controlled Vacuum leak, computer controlled.

If valve is acting up it can get stuck open.
After engine is warmed up and idling unplug the 2 wires from IAC Valve, valve will close all the way and RPMs should drop to 500, or engine may even stall, either is good irt means no vacuum leaks.

If idle stays high then you have leaks.

Now test drive with IAC valve unplugged, see if RPMs still hang high between shifts

 

[WillinHiFi]

thanks, will do. I also forgot to mention that when I bought it I found that the fuel pressure regulator was disconnected. I hooked it up but that was months ago.

 

[RonD]

Fuel pressure regulator(FPR) was disconnected????

If you mean the fuel line then you would have gas all over the place.

If you mean the Vacuum Hose was pulled off then it may mean fuel was being sucked into the engine because of a leaky diaphragm in the FPR.
Check that vacuum hose for fuel or fuel smell, replace FPR if fuel is in that hose.

Yes that could cause higher RPM especially when you let your foot off the gas pedal.
When you close throttle plate(take foot off the gas) at higher RPMs the vacuum in the intake goes up very high, this would suck in more fuel from that leaking diaphragm.

 

[WillinHiFi]

I noticed the o2 sensor fuse was blown, i got underneath it and the wires were alllll ****ed up so i got a new sensor and it runs like a top now!!!

 

[RonD]

Good Work

Thanks for updating the thread with the fix for the problem

Never would have guessed O2 issue with those symptoms

 

[WillinHiFi]

Good Work

Thanks for updating the thread with the fix for the problem

Never would have guessed O2 issue with those symptoms

No problem, it runs like a dream now.