tps 20% at idle

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May 12, 2005 | 11:11 PM

ls1m

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tps 20% at idle

My friend's got a 1999 F150 4.6 v8 that's running rough. using my scan tool, I saw the tps was at 19-20% at idle, and the engine load was 20-25%. Figuring he had a bad sensor, we replaced it, only to have the exact same thing now. It looks to be totally non-adjustable. What can I do? I removed the battery cable for a couple of seconds, hoping that would reset the computer, but it didn't work. There are no current or pending trouble codes.

Thanks
-Mark

May 13, 2005 | 12:19 AM

Racerguy

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Hi Mark and welcome to the forum

Rather than looking at % for the TP can you look at volts? It should be around .9V at idle.
Did you do KOEO and KOER tests?

May 13, 2005 | 06:23 AM

ls1m

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KOEO and KOER - I assume that's key-on engine off/running? Are you talking about the old eec4 systems where you plug in an analog volt meter & count the swings? I don't think this truck does this. It's a 1999 with obd2.

I don't know if my scanner will pick up voltage or not on that truck. There's 3 wires going to the sensor. Which two would I measure with a voltmeter?

May 13, 2005 | 08:25 AM

Racerguy

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Yes, KOEO is key on, engine off and KOER is key on engine running. On an OBD2 system you can't use a volt meter and count the swings. Apparently some scan tools won't do KOER but any decent one should.
I haven't looked at TP % before but was able to find it in the manual. It should be approx 17.4-19% at idle so you're probably close enough. The % is figured out based on voltage so you probably don't need to check that.
What does the engine do? How old are the plugs, fuel filter etc? Have you checked for vacuum leaks?

May 13, 2005 | 09:59 AM

ls1m

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We just changed the plugs. The old ones had huge gaps - .120 on one of them. That helped a little. I think the fuel filter is pretty new. I'll have to check some more things. I saw that 20% tps reading and figured it had to be the problem. Even the engine load was high, which I figured confirmed my suspicion. On my car, TPS is at zero & load is around 4% at idle. Oh, well, maybe he needed a new $35 sensor anyway.

The truck's just running rough and doesn't have the power it should. It's acting like a misfire. Maybe it's a plug wire or something.

Thanks for the help. How would I do those tests if my scan tool won't support it? Or is there a way to?

-Mark

May 14, 2005 | 08:31 AM

Racerguy

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With spark plugs that worn it wouldn't be too surprising if you had bad plug wires.
Your dealer can do a cylinder power balance on the road to see if any cylinders are misfiring and then you can go from there or you can just replace the wires and try it.
Has the MAF sensor ever been cleaned?
If your scan tool won't do the tests you'll have to take it somewhere that has one that will. You can't fake it like on an OBD1 system by counting light flashes or volt meter sweeps.

May 14, 2005 | 08:51 AM

ls1m

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The truck's out at the beach now. We were trying to fix it before a church surf trip, but I guess he made it OK any way. I contacted my scanner mfg and he says the test is in there, so I'll run that & test the plug wires & scan for misfires when he gets back. I really appreciate the help. I'll post what I find out.

Thanks
-Mark