8D, TPS Voltage dips below .53 causing high idle - Third Generation F-Body Message Boards

dkedrowitsch · 02-26-2009, 06:52 PM

Greetings!! Been a while since my last post...

I've got a 1992 K1500 pickup with a stock TPI 350 running speed density with a 730/8D (AUJP).

This all started with my truck's SES light flickering, setting code 33, and stalling when I took my foot off the accelerator. I had to 2-foot it the rest of the way. Once I shut off the truck and fired it back up, everything went back to normal. Without thinking much about it, I replaced the MAP sensor with a spare.

Several days later the problem returned...exactly the same. So the next logical step was to replace the TPS, since from what I understand about codes 33 and 34, the ECM expects the MAP value to be within a certain range when the throttle is open or closed.

I replaced the TPS with a new Wells part. Since then, I'm still having a problem, but somewhat different then before.

Now every few days (seems to be more often when it's above freezing outside) when I take my foot off the gas the TPS voltage will sometimes dip below .53v (sometimes as low as .18) for several Datamaster records. Eventually it recovers but at that point the ECM seems to have compensated the idle threshold to that previous low voltage, so once the proper voltage returns, the ECM reports 9-12% TPS and idles fast, keeps the EGR open, and causes my TCC lockup to cycle. One of the occurrences the TPS was actually jumping all over the place no matter where I held the throttle.

So far I've cleaned my engine harness ground on the intake, tried 2 spare 730s, and I didn't use my NVSRAM module in the current ECM.

Any opinions? New TPS bad? Wiring harness problem (hope not!)?

RBob · 02-27-2009, 08:51 AM

There is one item common between the MAF & TPS: they both use the +5 volt reference line from the ECM. If this voltage dips so will the MAP & TPS voltage.

RBob.