1995 4.0 rough idle
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1995 4.0 rough idle
Hello, I have a 1995 ford ranger with the 4.0 auto trans. When first starting the truck it immediately dies and only after a few attempts it stays running but it runs super rough. When I put it in drive with my foot on the brake the truck starts bucking and the rpm’s seam to drop and the truck starts almost bouncing. I have confirmed no vacuum leaks, have good fuel pressure, new spark plugs, and have checked and cleaned all the sensors on the intake system, iac, maf, etc. I am at a loss for what the issue could be. Any help is greatly appreciated.
Cross-Country
Joined: Jul 2025
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Hello, I have a 1995 ford ranger with the 4.0 auto trans. When first starting the truck it immediately dies and only after a few attempts it stays running but it runs super rough. When I put it in drive with my foot on the brake the truck starts bucking and the rpm’s seam to drop and the truck starts almost bouncing. I have confirmed no vacuum leaks, have good fuel pressure, new spark plugs, and have checked and cleaned all the sensors on the intake system, iac, maf, etc. I am at a loss for what the issue could be. Any help is greatly appreciated.
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Joined: Jan 2004
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From: SW Va
Lets think about this some more. Did the idle & rough running come about suddenly after some event, like the spark plug replacement ?
Idle speed is computer controlled using the IAC = Idle Air Control.
Is your 95 OBD-2 diagnostics with the scan-tool connector in cabin under the dash to the left of the steering collum, or is it still OBD-1 with the connector under hood ? in either case if you haven't already done so, scan for & post All pending or set trouble code clue Numbers, as they can help focus a trouble shoot.
More thoughts for consideration, let us know what you find.
Idle speed is computer controlled using the IAC = Idle Air Control.
Is your 95 OBD-2 diagnostics with the scan-tool connector in cabin under the dash to the left of the steering collum, or is it still OBD-1 with the connector under hood ? in either case if you haven't already done so, scan for & post All pending or set trouble code clue Numbers, as they can help focus a trouble shoot.
More thoughts for consideration, let us know what you find.
Cross-Country
Joined: Jul 2025
Posts: 51
Likes: 8
Hello, I have a 1995 ford ranger with the 4.0 auto trans. When first starting the truck it immediately dies and only after a few attempts it stays running but it runs super rough. When I put it in drive with my foot on the brake the truck starts bucking and the rpm’s seam to drop and the truck starts almost bouncing. I have confirmed no vacuum leaks, have good fuel pressure, new spark plugs, and have checked and cleaned all the sensors on the intake system, iac, maf, etc. I am at a loss for what the issue could be. Any help is greatly appreciated.
Trailering
Joined: Aug 2025
Posts: 23
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Some things can't be cleaned
They just need replacing.
IAC is hard to clean well without screwing up the electronics in it. Replace the PCV rather that clean a worn out one. Are the spark plugs at least single platinum? Plug wires ok? Does the air intake leak between the air filter and the throttle body? When you clean the EGR and/or IAC use new gaskets.
Clean the MAF sensor again.
IAC is hard to clean well without screwing up the electronics in it. Replace the PCV rather that clean a worn out one. Are the spark plugs at least single platinum? Plug wires ok? Does the air intake leak between the air filter and the throttle body? When you clean the EGR and/or IAC use new gaskets.
Clean the MAF sensor again.
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The issue ended up being a bad o-ring between the intake manifold and the egr valve tube that was causing a large air leak.
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From: SW Va
Since 95 was a transition year, might be helpful to know if your 95 Ranger is OBD-1 or OBD-2 diagnostics ? If OBD-2 & seeing as how you seem to like trouble-shooting your vehicle, maybe consider coming by the inexpensive ELM scan-tool as discussed here, as they can help focus a trouble-shoot. Low Cost ELM Scantool - Ford Truck Enthusiasts Forums
More thoughts for consideration.
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Sure, my truck is obd2 and was throwing a crankshaft position sensor code and an insufficient egr code. I went through all the sensors on the intake and tested them by unplugging them and seeing how it changed how the engine ran which did not make a difference. I then pulled spark plug wires while the engine ran to see if there were any cylinders misfiring which there was not. I also tested fuel pressure which was within spec. What gave the issue away was a hissing sound coming from where the egr valve tube connects to the plastic intake manifold. Apparently there is a little rubber o-ring that seals that connection and it had a very large leak that I could feel when I put my hand near the connection. I think this may have been caused by removing my intake when I cleaned it a month prior to the issue and I may not have gotten the o-ring back into place properly causing it to eventually fail.
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From: SW Va
Ok good feedback, since your 95 model is OBD-2 you can use the ELM scan tool & Forscan to do in depth trouble shooting for not too much cost.
With that bad of a vacuum leak fuel trim was likely corrupted & as well as the KAM = (Keep Alive Memory) fuel trim tables where they are stored.
So if its not back to running normal you could do a KAM wipe by disconnecting the battery B- cable for a few minutes before reconnecting, to completely discharge things so the ECM can begin building new uncorrupted fuel trim tables, if you haven't already one so .
With that bad of a vacuum leak fuel trim was likely corrupted & as well as the KAM = (Keep Alive Memory) fuel trim tables where they are stored.
So if its not back to running normal you could do a KAM wipe by disconnecting the battery B- cable for a few minutes before reconnecting, to completely discharge things so the ECM can begin building new uncorrupted fuel trim tables, if you haven't already one so .
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From: SW Va
Hold On, Don't disconnect the battery B- cable to wipe the KAM just yet!!!
Stumbled on your May 2025 Tranny Shifting thread where Mark suggested you use the ELM & FORScan to scan for tranny trouble codes & you never posted any code Numbers, so if you wipe the KAM now they'll be lost, along with any other stored codes that might help with the engine run trouble-shoot.
Also it'll wipe the engine learned but now likely also corrupted cold & warm idle speed strategy but this can be relearned on the next cold engine restart by following these simple steps to avoid possible tranny shift problems after a KAM wipe. high idle problem - Ford Truck Enthusiasts Forums
Stumbled on your May 2025 Tranny Shifting thread where Mark suggested you use the ELM & FORScan to scan for tranny trouble codes & you never posted any code Numbers, so if you wipe the KAM now they'll be lost, along with any other stored codes that might help with the engine run trouble-shoot.
Also it'll wipe the engine learned but now likely also corrupted cold & warm idle speed strategy but this can be relearned on the next cold engine restart by following these simple steps to avoid possible tranny shift problems after a KAM wipe. high idle problem - Ford Truck Enthusiasts Forums
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I haven’t wiped it yet, my transmission has shifted bad since I have owned the truck and every so often the overdrive light will start to blink but I have not been able to read the code.
I could not find the place to plug in the reader and just assumed my truck only had the ond2 port.
I could not find the place to plug in the reader and just assumed my truck only had the ond2 port.
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From: SW Va
You posted in your May 2025 tranny shift problem thread that you used a OBD-2 reader to pull a P0340 code, so the ELM scan-tool will plug into the same under dash to left of the steering collum OBD-2 DLC = Data Link Connector.
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From: SW Va
As Mark posted in your tranny shift thread back in May, a code reader isn't a scan-tool like the ELM / FORScan combo, that can query all of a Ford OBD-2 vehicles computers / controllers. A code reader usually only has access to the engine controller & tranny codes aren't stored there, they are in the tranny controller, so is likely why you can't find any tranny trouble code clues, as he posted.