hello all, I am having trouble with my bronco, it will not stay running on a cold start up unless I press on the gas a little. It is a 1989 302 auto trans. When I first start it up it will idle around 1500-2000 RPM's for a minute then slowly the idle will decrease and the engine dies, after a few minutes of running it will idle on it's own. This has been a problem since I have owned it. Recently I have replaced the plugs, wires, cap and rotor. When testing the IAC valve I get around 9 ohms which the book says it within spec but I get 12.17 volts to the valve when the manual says I should be getting 10.5 volts, Is this still ok? I have checked for vacuum leaks with a smoke machine found only a small leak at the vent on the charcoal canister. Does anyone have any ideas what I should check? Thank you in advance
will not idle when cold
- Thread starter 800snow
- Start date
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L\Bronco
Well-known member
Hey Snow, welcome to the zone.
The IAC voltage they refer to is likely across the valve with the engine running.
You may have a dirty throttle body or pcv issue causing the base idle to be too low.
Try warming it up so it will idle on its own, then unplug the IAC valve while its running. It should drop to 500ish RPM. if it stalls, the base idle is low, start by cleaning the sludge from the throttle body around and behind the plates, if that doesn't fix it, adj the throttle stop S C R E W in until it will idle at 500 with the IAC unplugged. then disconnect the battery for 5 min. Reconnect the batt and start it with everything plugged in, give it a good road test and check it cold later.
Hopefully that will work.
Good luck
Cheers
thanks, i will check those things
Yo 800snow,
Welcome to our Bronco site!
● Throttle Position Sensor (TPS) controls idle & transmission shift points
See these 1989 Ford Truck Service Manuals - Google Drive
Click "Drive" in pop-up
Includes:
1989 Ford Bronco Electrical & Vacuum Troubleshooting Manual
1989 Bronco & Ford Truck Emissions Manual
1989 Ford Car/Truck Pre-Delivery Manual
1989 Light Duty Truck Volume A: Body/Chassis/Electrical Volume 1 of 2 note
Google Drive "can't scan this file for viruses. It is too large for Google to scan for viruses.
." Although Google states, "Would you still like to download this file?" It CAN be downloaded and I found no virus reared its ugly head.
&
1989 Light Duty Truck Volume A: Body/Chassis/Electrical Volume 2 of 2
1989 Light Duty Truck Volume B: Engine
●
Haynes Red Manual for 80-95 Bronco & F Series @ Hanes guide 80-96 bko f series.pdf found by BroncMom!
See my mostly recovered site by my friend schwim @ https://web.archive.org/web/20101224072929/http://www.broncolinks.com/index.php?index=1
It contains boo-koo component repairs, installation & parts sources.
1989 Ford Bronco Dealer Brochure
1989 Bronco Lubricant Specifications by Ford via Gary
Welcome to our Bronco site!
● Throttle Position Sensor (TPS) controls idle & transmission shift points
See these 1989 Ford Truck Service Manuals - Google Drive
Click "Drive" in pop-up
Includes:
1989 Ford Bronco Electrical & Vacuum Troubleshooting Manual
1989 Bronco & Ford Truck Emissions Manual
1989 Ford Car/Truck Pre-Delivery Manual
1989 Light Duty Truck Volume A: Body/Chassis/Electrical Volume 1 of 2 note
Google Drive "can't scan this file for viruses. It is too large for Google to scan for viruses.
." Although Google states, "Would you still like to download this file?" It CAN be downloaded and I found no virus reared its ugly head.
&
1989 Light Duty Truck Volume A: Body/Chassis/Electrical Volume 2 of 2
1989 Light Duty Truck Volume B: Engine
●
Haynes Red Manual for 80-95 Bronco & F Series @ Hanes guide 80-96 bko f series.pdf found by BroncMom!
See my mostly recovered site by my friend schwim @ https://web.archive.org/web/20101224072929/http://www.broncolinks.com/index.php?index=1
It contains boo-koo component repairs, installation & parts sources.
1989 Ford Bronco Dealer Brochure
1989 Bronco Lubricant Specifications by Ford via Gary
I replaced the pcv about 500 miles ago, I got the engine warm so it would run on it's own, idle was a little above 600 rpm, i unplugged the IAC and the idle did not change at all after a minute or so i plugged the iac back in and the idle jumped up to 900 rpm and then slowly settled back down 600
thanks for the welcome,
I appreciate all the great info and now I have some reading to do
L\Bronco
Well-known member
Look for a vacuum leak, you base idle is a bit high, it should drop at least 100 when the iac is unplugged. Those used to eat the upper plenum gasket and sometimes the egr valve would wear causing a vac leak.
Run some water over those areas with a squirt bottle or a garden hose on low, it will make a slurping noise and idle rough when you hit the leak with no risk of fire.
Hope that helps.
Cheers
johnnyreb
Well-known member
maybe this will help you too. Yesterday I was working on my 78 bronco and thought. I would check and see if my NEW fuel pump was working. I took the NEW HOSE (ABOUT A YEAR OLD) OFF and put a new hose on and run it into a gallon jug of gas. The NEW HOSE---had rotted --REPLACED IT WITH A NEW HOSE. Put it in the gas jug FULL of gas. Started cranking the motor. VERY LITTLE GAS CAME OUT AND QUIT. So now I KNOW---MY NEW FUEL PUMP IS NO GOOD. --Maybe you need to check them. Sometimes RUBBER PARTS--ROT IN A FEW YEARS AND SOME PEOPLE NEVER REPLACE THEM. Vaccum hoses are a neglected part and will get cracks in them and when the motor is running and moving--can cause a leak.
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