Engine accelerates by itself!

[TremblantRanger]

First off, I've searched this forum as well as other ones, the net, and youtube to find an answer with no success... So I've got an '98 2.5 5-speed, with around 69000 miles. Sometimes, when I push the clutch in, the engine races up to almost 3000 RPM, and will stay there until I come to a complete stop, or sometimes it does that wile shifting gears. Also, I can be in gear coasting normally, and suddenly you can feel it accelerating, or going back and forth, or I can be coasting normally in 3rd, downshift into 2nd and instead of slowing down, it starts accelerating... I got no trouble codes, and the IAC have been changed maybe 2 years ago, but this started last spring. This problem comes and goes, weither the engine is cold or at operating temperature, and I can sometimes go for weeks with no problems, then it would come back for a week... Also, when it's doing it, shutting off the enginee and starting again seems to help. Other than that, the truck runs like a champ and I didn't notice any loss of power or fuel economy. I tried unplugging the IAC trick, but the truck idles and runs poorly if I do, which tells me that the IAC works, unlike when I tried it with my old IAC valve. Plugging my scanner for live data, everything seems kosher; coolant temp, intake temp, load and throttle position,, although these where checked at idle since it's hard otherwise while driving, without a datalogger. Any ideas? It's driving me nuts, and is sometimes sketchy and dangerous!!!!

 

[tomw]

I would check for the TPS - throttle pos sensor - being a little flaky. If the computer thinks the TPS is at X% open, it would supply more fuel, etc. Maybe check the PCV system will pull a slight vacuum on the oil filler @ idle using a post card or similar.
Last call is intake leaks. IMO
tom

 

[TremblantRanger]

Thanks Tom, I think you nailed it! I didn't think about checking the TPS sensor! I unplugged and plugged it a couple of times and the trouble now seems to be gone, and the truck seems to pull more smoothly! So I guess my next step will be cleaning the terminal and pack them with dielectric grease. Thanks again for the help!!!

 

[edward2016]

Get dielectric grease and electric contact cleaner. Spray the IAC plug and TPS plug with the cleaner and let dry. Then apply the grease to both plugs and reconnect. Start engine and let idle for few minutes. If doesnt work replace IAC

 

[TremblantRanger]

Get dielectric grease and electric contact cleaner. Spray the IAC plug and TPS plug with the cleaner and let dry. Then apply the grease to both plugs and reconnect. Start engine and let idle for few minutes. If doesnt work replace IAC

Thanks for the help Edward, but the problem is pretty much fixed! And the IAC is pretty recent too, and I did the tests and showed that it's working properly. But you're right, I'll clean and grease my IAC contacts and connector, just in case. Thanks!!!

 

[97ranger xlt]

would check also pcv valve. a bad one will cause a high idle and not throw a code...