TPS sensor questions.....weird readings after TPS replacement

**JRHAWK9** · 07-12-2007, 07:59 PM

OK, I recently installed a ScanGaugeII and have been monitoring different PCM things. I noticed that every once in awhile my TPS would go from 0% at idle to some random number, like 6%/8%/4% and I think I even saw an 11% at one time. All I would have to do is shut the car off and restart it and it would be back to 0% again. I decided to replace the TPS sensor with a Standard brand one from RockAuto.

I installed it and when the car is not running but when I have the key turned on I am seeing a TPS angle of 0%...great, that's what it should be! As soon as I start the car (warm or cold) it goes to 3% and my idle is just fine at around 800rpms. Now after I take it around a couple blocks my TPS reading at idle goes down to 2% and then a little bit later it will drop down to 1%. At this time my car seems to be idling at around only 700rpm's or so. Then when my TPS angle decides to drop to 0%, the idle goes back up to around 800 or so. I don't know how the heck my TPS angle could be changing like that, as I KNOW it's not physically moving as the sensor says it is. My IAC counts are in the 55 area. The car runs and idles just fine, just I am confused as to why I am getting these different TPS readings when the throttle is not physically moving.

I do have a ported/polished throttle body that had a bit too much removed around the throttle plate which allowed too much air through at idle. I had the guy who did the polishing aluminum weld my idle air hole shut because with it opened up my IAC count was VERY low and the car tended to idle a bit higher than it should and took forever to come down when coasting. Now with that idle air hole closed up, like I said, I am seeing IAC counts in the mid 50's with this new TPS sensor. I do recall that with my old sensor I was seeing IAC counts in the mid 20's....

BTW, my replacement Standard TPS sensor is spring loaded while the stock one I took off the car is not. Is the stock one supposed to be??? I would think it would be more accurate if it was spring loaded.

does anybody have any idea to why my TPS sensor seems to have a mind of it's own?? lol

thanks!!!

**LS2Tuner** · 07-12-2007, 08:46 PM

Could be multiple things seeing that it is a electric sensor running off a 5v reference.
It could be resisitance in one of the wires that changes with the heat under the hood. Or a loose terminal in the connector. Is your engine "clean" as in dirt and dust. I've had customers that put all that dressing shit under the hood collect so much dirt and dust it creates resistance on connectors.
I would monitor it with a dmm (digital multi meter).
Check the reference voltage and then check the TPS signal voltage.
You can back probe the connector with a paper clip without damaging any wires.

**JRHAWK9** · 07-13-2007, 05:31 AM

thanks for the reply

I have AutoTap so I don't really need to backprobe the connector, although I may have to to check the 5V reference, as I don't know if AutoTap scans that or not.

update:

I cleared the PCM and tried it again with the new TPS sensor....did the same thing and this time my idle was at around 1,000 rpms. I then swapped in my stock TPS sensor and all is well after I started it up. It had 0% TPS and my idle was ~800rpms. I think either the new TPS is bad or it is calibrated a bit different than the stock one....either way it definitely seems to be TPS related seeing everything is fine with the stocker back in.

**JRHAWK9** · 07-16-2007, 06:31 AM

problem solved....

found out my old TPS is bad as it read something other than "zero" after a while of driving when at idle. Tried replacing it twice with Standard brand ones (which is the brand I prefer for all ignition related components, Blue Streak is the high end brand of Standard) and both of them did not work, they would immediately start out at like 4% (at idle) and then randomly go down to 0% and then back up to some other number all the while my idle would go from 700rpm to around 900rpms. It's like my PCM was trying to "learn" the TPS sensor like it was not calibrated the same. At idle my TPS voltage was always between 0.50V - 0.60V (AutoTap only reads to the tenth of a volt, and it reads 0.5V at idle running), so everything checked out there. I will say that the Standard ones had -a lot- better build quality when comparing it to the stock AC one.

I then tried a cheap Wells brand from Autozone and that seemed to have done the trick. I also took notice that the Wells brand was 90% identical to the stock AC one. It had the exact same mold, exact same patent numbers stamped in it, exact same inerds and sloppy build quality and it even had the same molded in raised circle that the stock one has "AC" stamped in it. The Wells one had the molded circle but just didn't have the "AC" stamped in it. I am pretty confident to say that the stock AC sensor is made by Wells or they both are made by some other company.

**GNICTRY** · 07-16-2007, 06:53 AM

how did your car run with a bad tps? Hestitate?...

**JRHAWK9** · 07-18-2007, 05:11 PM

Originally Posted by GNICTRY

how did your car run with a bad tps? Hestitate?...

it actually ran fine with the exception of a slightly raised (50-75 rpms) idle when the sensor was acting up. The only reason why I noticed anything was wrong was I was monitoring my TPS with my newly acquired Scan Gauge II and saw that my TPS would sometimes go to something other than 0% when at idle. If it wasn't for that gauge I would have never known it, as one doesn't really notice 50-75 rpms on our stock analog tach. I also have no idea how long it was like that, could have been 2 weeks, could have been two years....