Hello I have a 94 Ford ranger 374000 miles and it's running on limp mode, I've replaced the throttle body sensor maf sensor and o2 sencer up stream with no luck it's still on limp mode I've taken the cat converter out and am not sure of the 02 sensor downstream would do any justice Any ideas on what else it may be? On very cold days it runs fine for alittle not nit then goes back into limp mode please help ty ,

 

What engine?

Not a 1994 if it has a downstream O2 sensor, that didn't start until 1995 when Ranger got the 104 wire Computer(EEC-V)
1994 and earlier had the 60 wire computer(EEC-IV) so BIG difference for diagnostics

Not sure what you mean by "limp mode", automatic transmissions can have whats called a "limp mode" where they start shifting harder less smooth

Computers have two modes
Open Loop, which is also Choke mode
Closed Loop, which is expected operating state after engine warms up

Open Loop is used before O2 sensors can be heated up, O2s need to be heated above 600degF to work, so 3 to 8min of engine run time depending on outside temp
In Open Loop computer uses air/fuel mix tables in memory, and runs the engine Richer(choke mode) and at higher idle for faster warm up

Closed Loop is when computer can use upstream O2 sensor feedback to fine tune air/fuel mix for best power and MPG

ECT(engine coolant temp) sensor can report engine is still cold after 5min, this could be because thermostat is stuck open or ECT sensor is failing, so no Closed Loop
There would be a code set for this and CEL(check engine light) would be on

Describe "limp mode" and confirm year of Ranger

1986 to 1994 EEC-IV computers have 2 or 3 capacitors that will fail and leak, this causes odd engine operation, easy to replace these, under $5 fix if that's the issue