Hi, I have a 2000 mercury grand marquis that is stalling at idle and sometimes loses power while driving around 45mph. I have changed the IAC, the MAF, the transmission has been rebuilt, the spark plugs are new, I have smoke checked it for vacuum leaks and found one and sealed it I checked it with carb cleaner to find any vacuum leaks. I have replaced the fuel filter. I have cleared the pcm using the battery ground disconnect with a jumper from positive to disconnected negative.I did not get a check engine light during any of the stalls. I did get an error on the brand new MAF so I got out my meter and needle probes and everything checked correctly, 12v grounds good, .9 on the number 1 wire and it went up with the rpms. it settled right down when the engine returned to idle. I pulled the MAF plug off and ran the car without it connected. The idle was dead on still, 800-ish rpm, MAF .24, and of course while revving that number didn't change. As soon as I connected the MAF harness back up things got strange again, and my code reader said that there was low MAF. P0102. I reset the codes. I captured the data while running the car and it got through 18 frames on my actron before dying. The fuel metering looked correct, mostly a little negative or 0, the MAF was .19 give or take. The engine rpm was good at 820 give or take, and then it increased the rpm into the 1100 range, dropped back to around 800 and then dropped to 540 and then stalled out completely. If you have any wisdom to share please pass it on. i am mystified. Thank you!! Mark Breton

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No. 1-3
thebreton
thebreton

I have another MAF I am going to connect and test, but I am fairly certain it is the pcm. What do I need to look out for if I purchase a used pcm? I read something about the car keys possibly needing to be "connected" to the pcm. Any wisdom from you would be most welcome.

thebreton
thebreton

Thank you for your reply. I am in the process of checking the wiring with a meter. I am going from the MAF harness back to the main connector for the pcm. I think after that it is computer replacement time. It's impossible to really see the wire colors going into that main connector, do you know of a link to an online pin out chart of what is right for this model and year?

ScottyKilmer
ScottyKilmer

Editor

maf data is all wrong, I would suspect wiring problem, bad main computer, massive vacuum leak on the intake system, Or just a faulty map sensor (those cheap chinese ones are often crap)

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