QZRBLU

I just had a few episodes of stalling today, it seems to stumble just off idle. I hooked-up my Snap-On scanner and the TPS values look good for my 1990 L98 6spd Idle= 0.80 and WOT=4.42 These readings are steady and repeatable. The TPS voltage climbs very smoothly from Idle to WOT with no drop-outs anywhere. IAC =115 and Learned=60
I did notice the Integrator jumps from 128 to 136 when it is stumbling but it is very intermittent. Requested RPM is 720 actual is 750 at Idle.
Nothing seems to be out of spec but I was ready to replace the TPS as the first step. The injectors are fairly new Bosch III's from Jon at FIC, installed a year ago. 35,700 miles on vehicle, New plugs a year ago too, same time as injectors. Fuel pressure is 49psi at Idle, vac hose connected to FPR, I turned it up a bit to get my BLMs correct with the new Bosch III's. Fuel pump voltage stays at 13.8V while running.
I was SURE this was a TPS going bad after all these years.

ANY ideas?

Thanks,
Mick
Tucson

aklim

Sounds to me like the ECM is opening it up quite a bit to achieve the idle desired. Did you get those readings while it was in closed loop assuming everything is off at the time and in good spec? I usually set it to about 20-30 counts on the IAC then set the TPS if you need setting.

QZRBLU

AK,
Yes, closed loop and everything off. The TPS is non-adjustable, auto calibrating. I have no way of setting the IAC motor. I did have to replace the IAC when the car was about a month old, it would cause the engine to die after an extended freeway run. It was very intermittent and the dealer wanted to keep the car for two weeks to see if they could recreate the failure. Fat chance of that! They would not let me borrow their "state-of-the-art" monitor at the time.
They later went out of business.

Thanks,
Mick

aklim

In all honesty you don't expect me to lend you my expensive tools and cut myself out of a profit, do you?

Yes you can adjust the IAC in a sense. Opening up the throttle let's more air in and the IAC counts go down. Turn the screw in and the butterflies open more, Rev and read again.

VikingTrad3r

op you should test the tps before just replacing it.

you should test everything before replacing it. its real expensive not too.

there will be a tps sensor diagnosis on the forum here. you need a multimeter. its very easy.

aklim

Much easier and accurate using a scanner. Cut the wire past your test point and while you are seeing something at the engine area, the ECM sees nothing. With the scanner he can check CTS at the same time and see if it is really right using an infra red thermometer.

antfarmer2

Is the o2 original?

VikingTrad3r

i

very true.

aklim

Sooner or later, you will need one, why not get it today?

Kevova

I suggest to get your min air rate and IAC counts where they should be 450rpm and IAC counts 10-30. Make sure timing is set to 6-8 degrees spec is 6 but some like 8 better. Make sure no carbon build up in throttle body. Your TPS is really too high at .80 with throttle closed. The EGR can come on as soon as throttle is depressed and possibly stay on after throttle is closed along with skewing IAC operation because ECM is seeing throttle is slightly open. If TPS is still over .60 I would either modify holes to allow adjustment or replace TPS with adjustable type. then reset TPS between .55-.60.

aklim

I wouldn't go off the rpm. That can be skewed depending on what the chip is set. I'd set it to 20-30 counts which should account for whatever the chip is set at.

For this purpose, I would not care what the engine likes or not. I'd set it at 6 so you can see what it is doing.

I don't think the EGR can come on like that. Certain conditions have to be met and not just be in closed loop.

QZRBLU

Viking,
I had planned on testing the TPS with one of my meters but the scanner gives me more information. The TPS is linear and repeatable at 0.80 and 4.42V, no drop-outs anywhere. Again, it is NOT adjustable, self-calibrating and it is within range of 0.36-0.96V
as far as the scanner data tells me.

Mick

aklim

True, there is no calibration but that does seem a little high. A couple things could be the issue. Your arm is bent incorrectly or placed incorrectly. Regardless, I don't think that we need to go there yet. I'd get the IAC settled first then search that direction. IIRC, .5 to .7 is considered idle even on 91s.

QZRBLU

Ant,
Yes the O2 sensor is original and the rich/lean counts look normal.

Thanks,
Mick

QZRBLU

TPS has never been touched since new, no bent parts. My scanner gives me an acceptable range for the TPS and it is well within that range.

QZRBLU

Kevin,
Where did you come up with that 450RPM idle speed? I've been all over my FSM and cannot find an idle speed spec for my ZF 6-speed. 450 sounds a lot like an auto in drive.
No EGR.
As I explained to AK, the TPS on this '90 L98 is auto-calibrating and is well within the range specified in the scanner.

Mick

aklim

The counts are one thing. It gets lazy after a while and reads but slowly which is why you should replace it after say 5 or 6 years.

aklim

What is the acceptable range? IIRC, it takes the first reading it has as base TPS voltage but after a certain amount, it considers it "off idle". So even if it reads between 1 and 4.5V, the 1 V part will make the ECM think it isn't idling or so I have read.

VikingTrad3r

I was wondering the same thing.

Any reading I have done on the tps is that it supposed to be set at .54

I have also read (it might not be right) that if it is set too high it messes with the ecu because you are telling the ecu your foot is depressing the pedal. personally i'd be getting an adjustable tps and putting it at .54

i suppose its possible that the 90 L98 does not have that requirement whereas my 85 and 87 do.

QZRBLU

The car only has 35K miles on it, O2 sensors are usually good for close to 100K miles.

Mick