Engine high rev start and stalls?

1995 FORD RANGER
180,000 MILES • 4.0L • V6 • 2WD • AUTOMATIC
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JEFF HERMAN
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I replaced the driver side valve cover gasket. I had to remove the plenum to get it out. The EGR pipe that drops from the plenum to the EGR valve broke and I repaired it. I didn't replace the plenum gasket but didn't hear it leaking and spraying carb cleaner around base didn't change rpms. The problem now is it won't stay running without holding the accelerator down. The engine runs very rough at 1,100 RPMs, smooths out at 2,000. If you start the truck it revs to 2,000 RPMs and immediately shuts off. It doesn't seem like there's much fuel pressure at the rail, but I was unable to test it yet. Would a weak fuel pump cause this? Is it more likely a TPS, IAC, or one of the other components in the emissions circuit? How can I test the components in the photos and what else might cause this? I cannot find any obvious external vacuum leaks.
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Dec 10, 2023 at 8:43 AM
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STRAILER
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This sounds like a large vacuum leak. Did it run okay before the repair? If so, I would go back and recheck your work. Also, we should run the codes to see if any are stored.

https://www.2carpros.com/articles/ford-lincoln-mercury-obd1-1995-and-earlier-diagnostic-trouble-code-definition-and-retrieval

Maybe a large vacuum line at the rear of the intake is off? This guide may help:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please upload pictures or videos of the problem so we can see what's going on.
Dec 11, 2023 at 4:17 AM
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JEFF HERMAN
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It appears to have an OBD2 connector under the dash behind a cover panel?
Dec 11, 2023 at 4:25 AM
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JEFF HERMAN
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It ran before the repair. I double checked everything and found no hoses off or external vacuum leaks with carb cleaner.
Dec 11, 2023 at 4:27 AM
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STRAILER
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It might have OBD2 because it is on the cut-off line, I would try plugging the scanner in to see if it reads codes. Can you upload a video of what the engine is doing? Also, I would check to make sure the EGR valve is not leaking internally.
Dec 12, 2023 at 3:42 AM
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JEFF HERMAN
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I'll be getting back to it Friday when the 40-degree heat wave hits.
Dec 12, 2023 at 3:46 AM
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JEFF HERMAN
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It was able to read live data through the port.
Dec 12, 2023 at 3:51 AM
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STRAILER
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Sounds good, I would be interested in the live data percentage for the IAC.
Dec 12, 2023 at 3:53 AM
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JEFF HERMAN
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I don't think my scanner can get that specific or I don't know how to use it. If the IAC doesn't open on startup would this happen?
Dec 12, 2023 at 3:55 AM
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STRAILER
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I don't think so if you do not have the throttle open slightly it should not start at all. I would check your work because you say it runs good before the repair so something must be incorrect. Please go over this guide:

https://www.2carpros.com/articles/stall-at-idle

Can you upload a short video of the problem? It may help us fix it.


Dec 14, 2023 at 2:34 AM
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JEFF HERMAN
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Here's a video of what's happening. The vacuum to the EGR is unplugged but I tested the valve, and it holds vacuum.
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Dec 15, 2023 at 1:57 AM
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JEFF HERMAN
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Update. The intake plenum seals leak a bit, I don't think the IAC is functional but the runs and idles smoothly when warm. The main vacuum leak was around the rubber grommet where the EGR pipe enters the intake plenum. It was not seated completely inside the plenum. It's difficult to do with a swollen grommet and the EGR valve attached to the manifold. There is an issue with oil accumulating in the air cleaner housing.
Dec 15, 2023 at 1:27 PM
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STRAILER
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Thanks for the video. I think I can hear a vacuum leak. I would use a smoke machine to help find the leak. Also, I would remove the EGR to see if you can blow through it which you should not be able to do.
Dec 16, 2023 at 2:44 AM
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JEFF HERMAN
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The video was before fixing the leak around the grommet. It runs fine for now but does need plenum seals and probably an IAC.
Dec 16, 2023 at 11:15 PM
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STRAILER
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Good call, a bad IAC can cause this as well. Let me know if you need any more help.
Dec 18, 2023 at 1:37 AM
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