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Ranger 2.9 Surging idle RPM


drewman26

New Member
Joined
Nov 24, 2017
Messages
6
Reaction score
1
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0
Location
GA
Vehicle Year
1987
Make / Model
Ford
Engine Size
2.9
Transmission
Manual
I am at my wits end with my truck.. It runs great above 1500 rpm but only sometimes idles. It goes up to 1600+ and down to 850 rpm and will rev back up. It will idle sometimes till you goose the gas and then it will start going up and down again. I've run three cans of seafoam through it and that helped some. The only codes in the ecm are code 34 for the EGR(its blocked off anyways) and code 89(The auto trans was replaced with an m5od) It did have code 41 but o2 sensor was replaced and that fixed it. The truck has been checked over thoroughly for vacuum leaks and none were found. The iac is circuit is causing the problem because when I unhook the iac it will go to idle and stay there. The tps has been adjusted so the truck will idle without the iac plugged in.


List of parts replaced and things done:


new IAC and gasket
Vacuum Lines
in-line frame fuel pump
both fuel filters
Plugs and wires
Cap and rotor
MAP sensor
ECT sensor
o2 sensor
new tps(was adjusted to .9 volts)
new PCV
Cleaned grounds
Vacuum lines for the EGR have been blocked and checked for leaks
FPR wasn't leaking and pressure was good
Changed the coolant and oil
installed new air filter


With the IAC circuit acting up i assume the ECM might be having problems finding idle?
If anybody has any ideas on what to do next I'd appreciate it!

Thanks,
Andrew
 
Last edited:


drewman26

New Member
Joined
Nov 24, 2017
Messages
6
Reaction score
1
Points
0
Location
GA
Vehicle Year
1987
Make / Model
Ford
Engine Size
2.9
Transmission
Manual
I have found the issue!

On that hunch of it being the ecm I went to the jy and pulled one from a bronco 2. It now holds an idle and runs better than ever!
 

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