05 Ford Escape Surging issues. Code P0511, have replace IAC, TPS, cleaned throttle body, fixed a vacuum leak off the MAP. Also replaced PCM and all plugs and coils because of an unrelated issue{apparently}....Any ideas?? Im at my wits end and so is my mechanic

Have you tested and cleaned the MAF?

Also look at the AAC valve, test for a vacuum leak and bad valves can cause this.

Did your mechanic test the harness (wiring) to the IAC?

I have not cleaned the MAF, Whats an AAC Valve? My mechanic has not tested wiring harness IAC, he claims it to be a costly time consuming process. Is that correct?? I'm thinking about taking it to a different mechanic for a fresher set of eyes.....

Auxiliary air control valve = AAC. Not sure if your model has this or relies on just the IAC. I would definitely test the harness because that is part of the P0511 code. An issue with the IAC system. A new IAC will not operate without the pigtail working. It does sound like you need a new mechanic. Maybe he said this because he didn't know how to do this and is just a parts changer.

Def taking it elsewhere for a fresher look. Its gotta be the wiring harness. How hard and expensive of a job is this? Any idea??

Not very for a automotive technician with the right electronic tools. If it is determined to be bad, then they will have to see if it is a control wire or a power feed and either solder the break or solder a new length and connector. 1 hour plus diagnosis in most cases.

Took it today to a different mechanic and they cant find anything. Wire harness has been tested and the car is not acting up for them. He's thinking it could be the PCM but that has just been replaced with a new one so now this mechanic has no idea either. This car only acts up intermittently and never when its in the shop. The only code is P0511.....so any thoughts??

Has anyone done a smoke test on the vacuum system? Do you have an electronic throttle body?

Vacuum leak was detected and fixed. Electronic Throttle Body? Maybe? I have replaced the TPS. Throttle body is clean and looks good. I guess I can start throwing more parts at it? Only thing not changed out would be the MAF Sensor, MAP Sensor and ETB. Seriously frustrated at this point. Could it be the new PCM? This was an issue before I had it replace so I'm kinda thinking no but who knows at this point...

I would seriously not throw parts at this but test these items and identify a faulty part. There are many YouTube videos out there to test all these listed parts. All of these are too expensive to just start buying and replacing. Every one of these last few parts you have not replaced could be your issue. They all have that ability to mess with your air/fuel/computer functions.

Not sure who you are taking this to but a true technician could find your issue. A bidirectional scanner with a scope and live data could determine what values are out of wack and direct them to the system or component not meeting its demand.

Your mechanic should be looking at rpms, recommended rpms, IAC %, throttle position sensor voltage and the voltage square wave on a scope to determine if it is indeed this IAC. I know you said you put a new one in but this 511 code points to this IAC. Is your gaskets new also?

Does it run better if you unplug either the MAF or the map sensor?

Has your mechanic tested fuel pressure? A clogged fuel filter will cause this surging. I have encountered this on a few cars in the last 10 years. Your pcm will overcompensate for lack of fuel and open the injectors.

I think so? I'll check. Fuel Filter was changed about 30,000 miles ago.

Replaced IAC 3 times. New Gasket. Have not unplugged MAF OR MAP. Not really sure how much tests & diagnostic have been done. I know they've run it hooked up to a computer looking for anything. At this point wondering if I should take it to Ford, maybe they'd better know what to look at.

Problem fixed. Mechanic could'nt detect problem so he decided to run a temporary jumper between PCM & IAC. Problem solved! Short was in Pigtail to IAC. Has been rewired now & is running good. Kinda frustrating that no one could detect this. The 2 different mechanics both said that unless it was actually acting up while its hooked up to a monitor then it wasn't detectable.

We knew it had to be the harness since it was a code for this component and you replaced the IAC 3 Times. Again, a true technician would have done a step by step follow the issue test and found this no communication issue with the wiring. Good to hear