Basics first, 1990, 6 speed, quite a few mods but stock bottom end.

So, I've read the long (I think closed) thread, and I've been looking all over in my factory Helms manual for the proper setting and procedure, with no success I might add.

IAC reset process was easily found but base idle was not even mentioned in the throttle body disassembly or replacment section?? Seems odd as I wouldn't think a replacement would be correct for every engine?

I understand to ground A/B to fully extend IAC & then unplug it to hold in that position.

TPS is NOT adjustable on my year. Though I have tested the output & it is in spec. & sync. w/ throttle position.

The closed thread mention a Factory bulletin that set-timing connector should also be disconnected? Just want to confirm who has a copy of the bulletin & if they would mind posting or sharing it in some form.

Base ignition timing being correct of course makes sense that it would also effect base idle stability.

Last detail... the correct base idle speed of 450.

Again, if I could find the base idle procedure & spec in my Helms manual I wouldn't even be posting in the first place. I'll keep looking though...

TIA & please, lets keep this short & to the facts.

 

After disconnecting the IAC, start the car and set the idle (called "minimum air in the manuals) usig the set screw top driver side corner of the TB. Once set turn off car and reconnect the IAC, Never seen any bullien about disconnecting the EST for this, but it wouldn't do any harm.

 

This is what I did:
I fully warmed it first, then did the procedure. ground A+B, turn key to on position, wait 30 seconds, remove IAC plug, turn off key remove ground. Start car @450 in drive using a scanner for RPM (mine was best at 500). Turn off, plug in IAC, press accelerator down about a 1/3, start run for a few seconds, turn off start again, should be close. Then TPS adjustment if nessessary.
Seem to remember the manual stating to disconnect the distrubter on mine, but with mods.I have it did not like that method. After I reset it that way (W/ est unplugged) it put it past the target RPM (idled to high, out of target range and IAC could not compensate) Mine is a 90 and I found that I needed to slot the TPS to get the volt range to .56, if not it would have been @.76.

*EDIT* I cannot find it either, don't remember where I read that but , if you notice in the 90 manual it shows a slotted TPS, and talks about setting it, so why the unslotted one like I have even though it does not give the correct volt reading ?

 

It would certainly make a difference. Even with my IACs working, my idle speed drops when I disconnect the EST to set the timing. With no air through the IAC, the idle speed (minimum air rpms, if you prefer) is going to be lower. Harm??? Difference? Definitely!

RACE ON!!!

 

I've done it with the EST connected and disconnected, no difference.

 

Thanks guys... I'm headed down to warm the car up now & check base timing, then ide, & finally, TPS (again just to be sure on that one).

 

I would be interested in knowing where the tps voltage is after you set min. air. without slotting it.

 

G killebrew says to disconnect the EST wire before setting base idle.




Put car in diagnostic mode for 30 seconds
Disconnect IAC
remove aldl jumper
Disconnect EST
Start car and adjust idle screw to 450 rpm
Shut car off.
For early adjustable-TPS cars, adjust TPS to .56 volts
Reconnect IAC and EST
Disconnect battery to clear codes.
Reconnect and start car. Should idle at about 700 rpm.

 

Are you doing this with the car in "P", or "D"?

 

90-91 ecm -727 accepts any tps input .3-.9 v and ''auto-zeros'' that as ''0'' throttle position....86-89 ecm -165 requires tps to be set to .55 v at min throttle

disconnect ''set timing connector''...if not disconnected, spark advance by ecm will not allow 450 rpm engine speed

 

Interesting. If that is the case, why would::G killebrew and redrose even address the EST? Every car *I* have observed idles faster as the timing is advanced (to a limit). Disconnecting the EST eliminates the ECM advance (retards the timing) and should lower the idle speed. Consequentially, that would change the minimum air adjustment to establish a given minimum air adjustment rpm. I don't have a TPI, but I can't believe that my engine works on different principles. Of course, I cannot speak for what YOU have observed or what you have witnessed your car doing.

RACE ON!!!

 

EXACTLY, which on mine was quite a bit of difference. That is why when I set it w/est disconnected, it then put the minimum air (idle) past the range that the IAC could compensate. ON MINE, leaving the EST connected was the only way to get it to work properly.

 

Depending on Year, one or two part Manual(s), you will find the Procedure in Driveability and Emissions, 6E3C2, Fuel Metering or Section 4 (Manual 2) Fuel. Some of the later Manuals do tell you to leave it alone and don't give a spec. Actually, there is little reason to do anything with it as the factory setting is deadon. If you check it and it's too low, clean the throttle body - the only way it gets below specs is because gunk is restricting air flow. If it's too high, air is getting in from somewhere else. Both scenarios assume that no one has played with it or that there isn't a Bulletin calling for adjustment (I believe the '86 has one raising the spec to 450, along with a Prom change - and there's a good chance both were handled by the original owner eons ago).

 

Okay just to follow up for those that asked:

Ignition timing was dead on at 6 deg. EST unplugged of course as otherwise you get like off the scale at around 10+??

Base idle was a little high at 600 but would NOT stabalize, kept going up & down by 50-100. I tinkered & looked for air leaks etc & finally got it down to 500 but it kept bouncing around up to 600. Below that it would NOT run.

TPS was .69 volts & went up smoothly. My manual did say that anything under .9 volts was fine, so I left it alone. Adjustment would mean making a slot myself, not something I felt like doing.

Plug everything back in, did the IAC reset start & run 5 seconds w/ part throttle, off for 10 sec & then restart. Idle at 750 RPM rock solid.

Being me I can't leave well enough alone though. I've had this TPIS 52MM throttle body sitting there for a couple weeks that I bought off a fellow forum member. I test the TPS on it & it reads. .57 volts at closed & goes up smoothly as well. What the hell, I quickly swap the throttle bodies, extend the IAC, pull the jumper & plug, fire it up. Car idles at 500 rpm, rock solid... I adjust it down 50 rpm to 450, reset everything & do the IAC reset again. Car idles perfect at 700 RPM in N.

My only complaint is the continued idle hunt when coasting up to a stop sign. As soon as the MPH goes to zero the idle drops & stays put. If the car is moving at all, (forward or reverse) it goes up & down from about 900 to 1050, slow & smooth like the IAC is hunting for some reason? Obviously tied somehow to MPH and/or righ/lean readings???

 

I think GM says +or -.08 on TPS which if base is .54 +puts it to.62 max. Slotting is very easy w/a dremel and a little carbide and will not hurt it. I would put it at .54 as recommended, unless you have had a chip burned and the tuner has said differently (same w/counts on IAC).
The other thing I noticed on doing adjustments was that it was important to adjust (min. air/idle) upwards in RPM, SLOWLY, doing it from adjusting min. air (idle) down did not give me as good of a result. I first brought it slightly below, and keeping it alive w/one hand and then bringing it up slowly w/screw adjustment, while watching RPM.
This may be redundant but I would double check, is (or was) the IAC in the new TB clean and a bit of oil on the shaft. Make sure linkage isn't binding on new TB., somehow didn't loosen any vac. lines during process.
A scanner would help to see if you are at the "target" rpm. as well as 02, bl., IAC etc. (presumming a non stock chip) as it still might be a bit out of range. hope this helps

 

He has a 1990 with a non-adjustable TPS. The ECM takes the minimum it is given, within a certain range, and accepts that as closed throttle. A different minimum that could be established by slotting the holes and adjusting the TPS voltage will have the same acceptance as closed throttle as the original or any other voltage reading within the acceptable range. In short, slotting the holes and adjusting the TPS, on a non-adjustable TPS car, will have no effect. The real difference in a non-adjustable TPS car, isn't the sensor and what is sends, it's the ECM and what it does with what it receives.

RACE ON!!!

 

At least on my 92 LT1 it makes no difference as the ECM compensates and zeros it out.
Jerris

 

Yes I understand and what you stated and is correct regarding throttle angle (still @0). (I believe that is what you are reffering to)
Mine is a 90, and it would stay @.74 volts, checked with both a digtal vohm and my scanner. After Iac adjusted even with it barely being able to idle was about .07, after IAC reconnect it went back up .074. And agreed, no matter what ammount there (within reason) will still give 0 throttle angle.

What I did noticed when voltage was adjusted on the TPS, and scanner on it, would be an effect on PW went lower as well as having a leaning effect (through watching BL, 02 and integrator). Or should I say, that is what it appears the ECM is doing with that information.

Another thing I find strange regarding the TPS is that the helms 90 manual states doing this adjustment for the TPS and shows an adjustable TPS. but as stated mine was also was a fixed position unit.
What I mentioned above is what I found when I was working with mine.