check line to fuel regulator if not pulling a vac right it will surge the idle much higherHello all, I am chasing an idle issue on my recently purchased ‘94 which now has approx. 69,000 miles and am hoping the group can point me in the right direction. I did own a near exact vehicle in the 90s so I know the behavior is not normal. The symptoms and what I’ve already done to try and resolve the issue are as follows:
- When purchased in July I noticed there was no high idle at cold start up and that on occasion the truck was slow to return to normal idle when coasting down to 0 mph.
- Being Summer, the lack of high idle did not affect drivability too badly however now in Winter the truck will not run/idle on its own until warm and is still very slow to return to normal idle when letting off the gas. When warm, it hangs at about 1,200 rpm and eventually drops to about 600-700 rpm 15-20 seconds after releasing the accelerator pedal.
- I have noticed that resetting the ECU by disconnecting the battery seems to resolve the issue temporarily however over a few days the symptoms reappear incrementally, almost as if a sensor is faulty and the ECU is adjusting for the faulty sensor which then causes the starting/idle issue to occur.
Having researched the heck out of the issue on this Forum and elsewhere I and my local Ford dealer have done the following:
- I inspected, cleaned and ultimately replaced the Idle Air Control Valve with an OEM (Hitachi) unit. I did reset the ECU and as described above this resolved the issue for only a few days.
- I adjusted the idle stop screw and ended-up with it where it was originally; no change
- Dealer replaced the IACV again with a Motorcraft part as it believed the IACV I installed was defective; no change
- Removed and soaked the Throttle Body to clean; no change
- Neither I or the dealer tech can hear a vacuum leak, though it was not smoke tested and I cannot guarantee there is no leak
- There is no check engine light and both I and the dealer separately confirmed there are no Ford-specific or OBD codes
Any suggestions on next steps? MAF? Coolant Temp Sensor?
Thanks in advance.