I'm retired, and trying to figure this out. Erratic idle any time. Start up, while driving, stopped at red light. Sometimes normal, more often than not up, and down. No vacumn leak, good comp, no loss of power, gas mileage(20mpg). Changed all sensors, no diff. Changed IAC. New from ford. Diff. Unplug iac and engine behaves normal. Upon startup, I just keep idle up till warm and its idles fine. I've also changed the brain. Along with the pcv valve, and rubber grommet on the valve cover. WHAT'S MY PROBLEM?
If there are no vacuum leaks and you replaced the IAC, I have to ask if you have checked engine compression and the coolant temp sensor?
June, 26, 2014 AT 8:02 PM
No I have not changed the temp sending unit. Have a code scanner and
that part has never come up. Always the others as possibilities, one after another. Everytime, I changed something, it would be fine, but return after a short time. Thank you for the input. Will pursue temp sending unit.
June, 27, 2014 AT 8:05 PM
Also, if you haven't cleaned the throttle body, give that a try.
Let me know what you find. Also, keep in mind with this many miles, compression could be weak when cold and as it heats up, everything expands and improves compression. It's just a thought.
Let me know what you find.
June, 28, 2014 AT 4:53 PM
had senior moment. My truck has that many miles, the engine was sucking antifreeze in two cylinders. That eng had all these issues. It ran fine. Blew a head gasket, so I had another engine installed.
It had 79000 miles, had been checked out. Compression, leak down, valve covers, and oil pan pulled and checked for sludge, came with a 3 year warranty. The installer put my outers on, ( starter, alternator, etc. Otherwise a complete engine. Used all my electronics. Added complete tune up, timing, coolant, hoses, etc. My problems stayed with the truck. I've also picked up 2-3 miles per gallon. It runs great, more pep. Just this persistant problem. My code scanner never indicated the coolant temp. Sensor. I will call the ford garage on Monday for a new one. I did not know that there were two coolant sensors. One for the temp. Gauge, and one for the computer. Thank You,
June, 28, 2014 AT 6:39 PM
Please understand, the sensor is a guess at this point. I would hate for you to spend money where you don't need to. Also, if you determine the sensor is the issue, I would just get one at a parts store. It will be much cheaper.
Can you read live data with your scanner? If so, check out the CTS and see what it is reading.
June, 28, 2014 AT 6:40 PM
After thought. Do you have a timing light? If so, check the timing and see if it is jumping around and not steady. Let me know what you find.