aklim

Correct. You are MAF and 90-91 is Speed Density so it takes the initial voltage as base. IIRC, it considers anything past 0.72 to be part throttle. Not sure what that breakpoint is.

aklim

But the car is how old again? You have no idea what fuel was going through it. Yes, we all have gotten a batch of bad fuel or so so fuel. It isn't horribly expensive and probably should be changed after 5 to 10 years at the outside. Even fine wine goes bad after a bunch of years.

QZRBLU

Correct, the '90 L98 has an auto-calibrating TPS, it reads the closed throttle voltage and remembers it, in my case it's 0.80V and I will now
go to the garage, hook-up my scanner and write down the acceptable idle voltage range, I 'think' it's around 0.65 to 0.96V but I will check.
UPDATE: The acceptable range for closed throttle is 0.36V to 0.96V

Mick

antfarmer2

Mine never showed a code but were original new o2s what differance.

QZRBLU

I just hooked up the scanner (Snap-On MT2500) and warmed the engine up and watched it go closed loop. O2 mv reading in closed loop is 105mv and it jumps instantly to 805mv when I blip the throttle and make it rich. Idle IAC is 69 and Learned IAC is 65. Desired idle (warmed in the garage) is 738 and actual idle is 750. The acceptable closed throttle TPS range is 0.36V to 0.96V, actual closed throttle is 0.80V and WOT is 4.42V It did NOT stumble today.

QZRBLU

Only one O2 sensor in the driver-side Y-Pipe, I may order one and just replace it.

Mick

QZRBLU

Every drop of fuel through this engine was pumped by me and until I moved to AZ, every drop was Shell premium and we just got a new Shell station 1/2mile from the house. Over here in AZ I've been using Quick Trip Premium (Tier 1 fuels). I ordered a new Delco O2 sensor just because of the age, even though the original responds instantly.

Mick

aklim

You also watch what has been distilled and put into the tank? There is a smaller chance of bad gas with name brand gas but not every drop is perfect unlike what they got you to believe

Dt86

You're running rich for the o2 to be at 800. It should be flagging back and forth which indicates the computer is making corrections to keep it at the correct air/fuel ratio. Your IAC is trying to compensate by opening up to allow more air in. You need to find out WHY it's dumping fuel. TPS setting for my 86 is .54 at idle.

QZRBLU

No AK,
I do not watch the distillation process but I DO buy top tier fuel.

I had the car out for a short trip this morning, no stumble even after it got warmed-up in closed loop. I have a new O2 sensor coming tomorrow and the car is up on the lift until I get that replaced. I will also pull the IAC to see if there is any carbon build-up.

Mick

QZRBLU

Thanks dt,
It is constantly switching rich/lean while it is warm. I can cause it to go Rich blipping the throttle. Your TPS is different and NOT auto-calibrating like my '90. L98's with a MAF sensor like yours have an an adjustable TPS, I don't.

MIck

Dt86

Ah I thought your O2 was staying high. Your IAC is still really open though.

aklim

Point is that I have also done the same and on some loads, notice a higher knock count doing the same thing and top tier fuel doesn't guarantee perfection. All it does is dump a little more detergent which apparently doesn't even keep the injectors clean since I see a difference in flow rates before and after cleaning.

QZRBLU

UPDATE: New O2 sensor installed and IAC motor removed to check for build-up on pintle. Pintle was dark but had no build-up, all throttle passages were clean, even under the top cover. It's been raining here most of the day, so no test drive today. I will hook-up my scanner and do a test when this rain blows out of the area, maybe tomorrow.

UPDATE: I've had the car out several times between storms and I noticed
no hesitation or stumbling. It MAY be fixed, we will see.

Mick

antfarmer2

Hell with that put your butt in the seat and drive it.

aklim

Hopefully with the roof on.

QZRBLU

Nope,
It's spotless right now and I don't want to clean it again just for a test drive I can do any day this week with no rain in the forecast. I will update with any changes (I expect none).

Mick

aklim

But if you sprayed carpet shampoo and drove around, it might clean out your inside too.

aklim

After seeing that C4 last week driving in the storm with the top down, I kinda got addicted to seeing things like that. Don't ask me why he did it. If I were driving, regardless of what the weatherman says, I will have my top on and if I took it off, it will be in the back. This guy was driving down the highway with the top off in the storm. Even the bikers have enough sense to hide under a bridge or pull off somewhere dry.