hfx_guy

Hi, I'm new to this forum. I have a 94 1500 4X4 with 5.7. Sometimes (its not consistant) I get an idle and drivability problem. At idle, it will rev to 1300, down to 700, to 1400, down to 500, then to 1400, and down to 300 and stall. Also, when driving, it will not respond to the throttle, just stall. When it is up to temperature, the problem seems to go away. There have been no codes set, although sometimes the check engine light comes on. I have a new o2 sensor, and coolant temp sensor. Any ideas?

RABarrett

As any engine ages, some deposits are left on the throttle body, especially on the passages used by the Idle Air Control. These deposits are also left on the pintle of the same device, causing erratic idle control. These deposits are typically either the loose type, which can shift on the surfaces, or the hard type, which just make things stick. You might try cleaning both of these surfaces, w/ carb cleaner and a rag. Reinstall the IAC, cycle the key, restart the engine and allow the computer to reestablish its correct relationship. Ray

xjoeharperx

Be sure to check the egr valve..if it is open when you come to a stop it will cause the same problems. It too suffers from the carbon deposits that RABarret spoke of.

Bronco2

Some thoughts-in my expierience a check engine lite on a OBD1 vehicle and no codes indicates bad plug wires. The s/p wires "leak" voltage to the wiring harness, confusing the ECM. You may also want to disconnect a major sensor (like the coolant temp) flash code the truck and see if the ECM is remembering codes. Cleaning the T/B and EGR wouldn't hurt a thing. Please post the cure.

hfx_guy

Thanks everyone, I will post what happens.