EB - MAP Sensor Cleaning - Rough Cold Idle

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G213

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Hey All-

I've done a ton of reading on the Ecoboost 3.5 engine and read the many many comments made by owners regarding a slightly rough idle on cold start. However after the first minute or so of driving, the rough idle disappears. My truck has the same symptoms.

I've heard of mainly three causes....

1. This is a normal characteristic of direct injection engines.
2. The ECU purposely runs a rich fuel mixture at cold start to quickly heat up the catalytic converters to meet emissions standards.
3. Carbon build-up on the backside of the intake valves.

So those are all fine and if you told me definitively it was one of those, I'd probably believe it. (However, I'd be less convinced about number 3, since the borescope videos I've seen show remarkably clean intake valves on high mileage 3.5 EBs. Apparently FoMoCo has a patented timing technology which briefly keeps the intake valves open during the fuel injection stroke to give them the benefit of gasoline detergents.)

But here's something interesting....

I found a video on youtube of a guy with a 3.5 F150 who demonstrates a rough cold idle. He gives instruction on how to remove and clean both MAP sensors and the MAF sensor.

I've done this procedure twice now on my truck...each time clearly seeing and removing light gunk covering the topside MAP sensor. Upon the very first cold start after cleaning, the truck idles like a kitten...hardly any rough idle at all. But after that first idle, it goes right back to the way it was prior to the cleaning.

Is that because the ECU readjusts to the clean sensor after the first cold start? Or could it be that it's just ready to be replaced? The actual sensor itself is clearly discolored compared to the other MAP sensor (i.e. the top MAP sensor is brownish whereas the throttle body MAP sensor is white)

Let me know what you think.
 

dnicholas47

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Did you reset the PCM too? I did this last night, but mine felt like it was tougher than normal. I bought this truck used, and judging by the amount of gunk on the topside sensor, I would say it had never been done.
 

16plati

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Hey All-

I've done a ton of reading on the Ecoboost 3.5 engine and read the many many comments made by owners regarding a slightly rough idle on cold start. However after the first minute or so of driving, the rough idle disappears. My truck has the same symptoms.

I've heard of mainly three causes....

1. This is a normal characteristic of direct injection engines.
2. The ECU purposely runs a rich fuel mixture at cold start to quickly heat up the catalytic converters to meet emissions standards.
3. Carbon build-up on the backside of the intake valves.

So those are all fine and if you told me definitively it was one of those, I'd probably believe it. (However, I'd be less convinced about number 3, since the borescope videos I've seen show remarkably clean intake valves on high mileage 3.5 EBs. Apparently FoMoCo has a patented timing technology which briefly keeps the intake valves open during the fuel injection stroke to give them the benefit of gasoline detergents.)

But here's something interesting....

I found a video on youtube of a guy with a 3.5 F150 who demonstrates a rough cold idle. He gives instruction on how to remove and clean both MAP sensors and the MAF sensor.

I've done this procedure twice now on my truck...each time clearly seeing and removing light gunk covering the topside MAP sensor. Upon the very first cold start after cleaning, the truck idles like a kitten...hardly any rough idle at all. But after that first idle, it goes right back to the way it was prior to the cleaning.

Is that because the ECU readjusts to the clean sensor after the first cold start? Or could it be that it's just ready to be replaced? The actual sensor itself is clearly discolored compared to the other MAP sensor (i.e. the top MAP sensor is brownish whereas the throttle body MAP sensor is white)

Let me know what you think.
Thts bc you don’t have a catch can to collect that gunk before its blown all over the MAP sensors. You shouldve done a KAM and PCM reset after cleaning
 
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G213

G213

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Did you reset the PCM too? I did this last night, but mine felt like it was tougher than normal. I bought this truck used, and judging by the amount of gunk on the topside sensor, I would say it had never been done.

So interestingly enough....I did this again with the PCM reset and saw no difference...the idle stayed rough on a first cold start.

Only with the sensor clean and no reset did I get that super smooth idle for that first cold start.

Either way it went back to normal after the first drive.
 
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G213

G213

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Thts bc you don’t have a catch can to collect that gunk before its blown all over the MAP sensors. You shouldve done a KAM and PCM reset after cleaning

I do have that gunk on there whenever I clean the topside sensor, so valid point. Seems odd that they wouldn’t catch that as a design issue during engineering. Maybe they thought most owners wouldn’t be bothered enough by the rough cold idle to do anything?
 

16plati

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I do have that gunk on there whenever I clean the topside sensor, so valid point. Seems odd that they wouldn’t catch that as a design issue during engineering. Maybe they thought most owners wouldn’t be bothered enough by the rough cold idle to do anything?
Change your plugs?
 
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G213

G213

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How many miles on the truck? Maybe time for a spark plug change.

Ah good point. 51,500k

BUT, did change them all out at 46k. Used Motorcraft plugs SP-534 all gapped to .030 (verified gap on each before installing)

I know some people said gapping to .028 might help, but I haven’t tried.

Like many others, the factory plugs were gapped all over the place...from .028 to .040
 
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sixsix

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Ah good point. 51,500k

BUT, did change them all out at 46k. Used Motorcraft plugs SP-534 all gapped to .030 (verified gap on each before installing)

I know some people said gapping to .028 might help, but I haven’t tried.

Like many others, the factory plugs were gapped all over the place...from .028 to .040

I'm at 70k and haven't changed them yet, I've been meaning to but just been too busy. I get the occasional rough idle at start up too, sometimes it'll shake pretty good when I put it in reverse to back out of the garage, almost like it wants to stall, but then it's fine after that.
 

16plati

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Ah good point. 51,500k

BUT, did change them all out at 46k. Used Motorcraft plugs SP-534 all gapped to .030 (verified gap on each before installing)

I know some people said gapping to .028 might help, but I haven’t tried.

Like many others, the factory plugs were gapped all over the place...from .028 to .040
.028” if you’re tuned
 
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