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2.3L ('83-'97) 97 2.3 5 speed lurches when taking off in gear and when under load


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Howdy yall, got an issue with my Ranger.

So, when taking off in first, it'll act fine for a second but when I start to get going, the thing acts like I put my foot down even more, when in reality I left the pedal at a steady position. It'll even drive forward with no throttle input after it begins to do this. It also does it when driving down the road. It's like a surge of power that I didn't even ask for.

I unplugged the IAC and TPS one at a time to no change, however, when I unplug the MAF it does not do it at all. Cleaned the MAF sensor with no change.

I plugged the truck into my laptop with FORScan, and observed no weird readings on the MAF, IAC, or TPS. The truck does seem to do this "lurch" when the engine is at or above ~45% load.

It has done it since I got it, but in the course of 2 days its gotten way worse. If anyone has any input on what I can do to fix this I'd appreciate it.
 


RonD

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When you unplug the MAF sensor the computer goes into partial open loop so its not processing most sensor data, like a "safe mode"
Its possible its a MAF sensor issue, but usual failure mode causes bogging, less power, not more, but as we all know, anything is possible, lol

Is the IAC Valve Motorcraft or Hitachi brand?
Those are the only ones that work with Fords, other brands will cause odd issues
When you unplugged the IAC Valve engine should have idled very low or stalled, did that happen?

If data all looks OK then its most likely a mechanical issue, some thing computer can not "see"

Check throttle plate for looseness could be opening a bit more suddenly

Replace PCV valve if its been awhile, these will get sticky and its a controlled vacuum leak, so if it suddenly changes position engine will REV
PCV valve is held closed by high vacuum in intake, when you open throttle vacuum goes down and PCV Valve should slowly open, SLOWLY OPEN
From your description when vacuum goes down you are getting a surge in RPM, which means MORE AIR is coming in
So PCV valve would be likely candidate
And no, shaking them and feeling weight move is not a 100% it works test, lol
 
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RonD

I bought a PCV yesterday with the intention of replacing it. Well they sold me the wrong one. No big deal. I also bought new plug wires. The ones on it were original and definitely needed replacing. Got them changed out and away goes my "surging". The truck runs better now too.

Any explanation on why old plug wires wouldve caused my issue?
 

RonD

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Sure, if they were arcing or had too much resistance, but I would expect that to show up more when engine is under a load, not surging at idle
Go back over what you needed to move and/or disconnect and reconnect when changing the plugs and wires

Out side of the physical size of PCV Valve they are all the same, all gasoline engines run the same vacuum levels
 

cstarbard

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On my 94 2.3, The IACV used to get stuck open, and the truck would cruise ahead without my foot on the pedal. It was obnoxious. It would even sometimes accelerate when this happened. A build up of carbon in the IACV would create friction or something and prevent the little valve from closing.

I would think that if you were having this problem, unplugging the IACV would change nothing, since the valve physically gets stuck open. Whenever this happened on mine I just cleaned the IACV with isopropyl alcohol or other mild solvent and q tips and the problem would go away.
 
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cstarbard, ill try that, thanks!

RonD, changed PCV, didn't improve anything.
edit - also it doesnt surge under idle. it surges under load.
 
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