94 Explorer surges

[rbarbourbis]

Truck used to idle, slow down, cough and surge. It would do the surge on idle or driving. I've thrown a lot of new parts at it and have resolved much. But, it still throws the 124 TPS high code (no other codes) and sometimes surges while driving. Lately, it doesn't do it idling. Could this be some kind of grounding issue maybe with the fuel pump? Or would that throw another code?

New parts
plugs (needed anyway)
wires (needed anyway)
TPS
MAF
IAC
DPFE
EGR
EGR tube (needed , broke when I moved it a little)
EGR switch
O2 sensors (both)
Air Charge Temp sensor
Fuel filter
Several vacuum lines (hard ones broke when moving them around)
Vacuum seems good all over now.
Have not replaced fuel pressure regulator.
Not much else to replace or test that I know of.


Any ideas what would still be causing the surging? My wife says it does it when I'm not driving. Guess it likes my driving better

Thanks,
Randall

 

[walterd140]

I would initially tell you to find a vacuum leak, but you say that's good. Only thing you didn't say you changed was the air filter itself. But I don't think that would be the cause anyway.
How about the fuel itself? What octane & how much do you put in? Maybe a shot of octane boost to see if that helps?

 

[MrShorty]

I suppose anything is possible, but I don't see a fuel pump ground issue being related to a CM124 code. Any fault in the fuel pump circuit could create a "cough and surge." First step I would probably follow, if I wanted to follow this line of thought, would be to put a fuel pressure gauge on the fuel rail and see what the fuel pressure is doing when it "coughs and surges." My own experience suggests that the engine will run normal over a fairly wide range of pressures. Spec (no vacuum to the FPR) is 35-45 psi. I've seen my engine run normal until the pressure gets down near 20-25 psi. A fuel pump problem should be pretty obvious, as the pressure will drop significantly.

Other than replacing the TPS, what diagnosis have you done for the CM 124? Since the CM124 seems to keep coming back (I'm assuming you've cleared the code after making repairs), I'd probably focus my efforts on the TPS circuit. Remember that trouble codes point to a problem in a circuit, of which the sensor is only one part. 1st thing is to determine how repeatable the fault is. If you clear CM, does the CM124 come back immediately, or do you have to drive it a while (until the first instance of "cough and surge"?) before the code comes back? If it comes back immediately, then the fault is more consistent and will be easier to track down. If it takes a while, can you pinpoint any specific conditions that seem to trigger the code/cough/surge?

 

[John4me05]

Sounds exactly like what mine did when a vac line slid off from tranny fluid and the vac mod. Double check that to be sure. It rocked the truck, acted like it had a monster cam, then smoother out and then repeated. idle went down to 400 or so and then when you flick the throttle it would idle down horribly slow.