My 2002 ford ranger with a 4.0 litre SOHC(75k miles, engine
is solid) is burning rich and the RPM's are fluctuating and some times stalling out.
When the check engine light is on, the truck seems to run good. When I disconnect the positive cable to the battery and turn the check engine light off, the truck starts to run bad again. Then the check engine light comes on again after driving it a while.
I replaced the throttle position sensor, cleaned the throttle body and air intake, ran lucas fuel injector
cleaner through it, and I sprayed starting fluid around the engine pretty much everywhere to check for vacuum leaks(none found).
I took it to the Ford Dealer and they ran a computer test and asked if I could bring it back for more diagnostics tests on Monday (it was a Saturday and they ran out of time).
The Service tech asked me if it was the original engine, if I replaced any parts, etc....
The truck was wrecked when I bought it and I had the body repaired. It got hit pretty hard. My body guy may have possibly replaced some of the components such as air intake or other things from another wrecked truck.
Again, the symptoms: RPM's Fluctuate when starting (hot and cold) and wants to stall and then settles at roughly 800 steady. Burning rich. Check engine light comes on.
Other than that, the engine is strong and runs great. No smoke but I do notice possibly excess moisture coming out of exhaust
(may be normal, not sure).