1994 Olds 88 3.8 w/ 60,000 original miles since new

Idle speed varies between normal and about 2000RPM at times.
Engine runs very smoothly.

I replaced the IAC (Idle Air Control Valve), but it still does it exactly as before.

NOT a vacuum leak.

If the car is running at 2000RPM, just turning the ignition off and re-starting it (not touching the throttle or anything else) usually causes the idle to be normal again (until the next time this happens).

Otherwise the car runs and responds to throttle normally.

Only other symptom is that it won't downshift from overdrive/torque-converter locked up with throttle. Upshifts are normal.

Any ideas?

Have you tested your TPS sensor?

I know yours is the Series1, but the test is the same.

https://www.gmforum.com/trouble-shoo...sensor-279319/

I looked at it today and thought of doing so w/ an ohmeter, and unlike my '96 Bonneville SE (I miss that car), the '94 Olds mounted it so I don't know HOW the heck to access the Philips mounting screws a few mm away from the exhaust manifold beneath it (w/o pulling the throttle-body to get at them).

I suspect I should have just bitten the bullet and replaced it for age at only $35, but testing it in-place is a lot easier. Thanks for the reference.

I cleaned the fine-wire air flow sensor w/ some CRC spray I bought for another car, and it looked clean, as did the interior of the throttle body assembly (I expected to see some oil/sludge in there).

Thanks-

You should probably use MAF sensor cleaner, which surprisingly sits right next to the carb/choke cleaner. Carb cleaner leaves a residue that can interfere with the sensor.

That'* exactly what I did use, in fact; not carb cleaner.
Sits right next to the cab cleaner on my shelf, too.
It was about $6 so it doesn't get used very often.

Thanks

Tested the TPS today using an ohmmeter.

Reading jumped all over the place as the throttle was slowly moved, so maybe this is the source of the poor idle rpm regulation.

Ordered one from Rock Auto.

Hopefully this will remedy the situation.

I'll let you know...

Bob

Thank you, please keep us posted.

Changed TPS (out of 2 dozen screw drivers, naturally none was the perfect length to get to where they mounted the TPS close to the EGR and the cross-over exhaust manifold) and so far, so good on idle speed.

Now I am back to trying to figure out why after starting sometimes something knocks REALLY badly 2-3 times. Once the engine is at idling speed, all is well, and it doesn't do it every start-maybe 1 out of 5. It'* dramatic enough it sounds and feels like someone is striking the engine block w/ a BIG hammer, and the engine mechanically pulses each instant it knocks (as if it is hanging up on something mechanically for a brief instant).

My feeling was that it was a loose bolt in the bell housing that occasionally flips and gets caught between the torque converter or the flex plate and the housing itself, then flips out of the way again.

Yesterday, the starter quit, giving me the opportunity to examine. Odd that at 60k miles since new, the solenoid quit (no click, but there is voltage at the solenoid terminal, so it'* a dead solenoid for sure).

I dropped the starter, and it looks fine (though obviously I am going to replace it), but I carefully examined with the inspection cover (where you get at the flexplate-to-torque converter bolts), and I can clearly see an area around the T/C shiny steel (outboard of the ring gear teeth) where something has been rubbing, and there are some shallow "dents" as well that I imagine are caused when it "bangs" loudly.

I inspected carefully w/ a flashlight, and probed around w/ a magnet wand, and had someone turn the crankshaft while I looked and probed in the bell housing as well as I could, and I could find absolutely NOTHING down there at the bottom where one would expect to find something loose like that.

Any ideas what it could be causing this, or what could be loose and getting into harm'* way at times?

The rub marks are all around the radius shown with a RED arrow in the photograph that is at this Copy-and-Paste Link: 2013-06-29_0929 - bobinyelm'* library

The narrow rub/scratch mark all around the T/C not that shiny in the photo, and the small shiny indentations are on the other side (but in the same area the arrow points to). They are all in the radius of the T/C right at the arrow-point.

Any ideas or suggestions most welcome as I am sure that at SOME point, whatever it is may do some actual damage to the T/C or something else.

I'm going to post this as a separate thread as well so maybe more folks not following this thread will see it, so if you have ideas, post them here, or there. I'll title the Question "Something loose in my Bell Housing?"

Bob