RichS 1986928

86.0 Car was idling ok before I changed the fuel Chip to one of Porken's
new LH22r/55. Now It's hunting between 700-800 RPM. I already had in the
new EZFr chip and it was idling pretty well before this.

I've taken care of all the usual suspects recently.

O2 sensor is 5years 10,000 miles old.
MAF Adjusted last year at injection labs in Boulder
ISV new
TPS new, adjusted and working
Fuel pump/filter, new
Injectors, new
Fuel lines, new
FPR, New ('87 unit for the fuel chip)
Vacum lines newish.
I even replaced the orings in the Throttle Body trying to eliminate
any unmetered air.

When I adjusted the throttle bypass screw (w/B&C shorted), if I try to
turn the idle down to 750 or lower the car stalls. I needed to set it
at approx. 800RPM just to keep it runnnig.

Vacum is at 15psi, Ken thought maybe this was low and I should check
my timing. I need his tool to do that..

Anyone have any other thoughts on the problem? I'm hoping maybe the
bypass screw results are a clue to the root cause.

Mrmerlin

try setting the MAF to about 167 ohms check it through the harness pins 14 and 25 of the LH, IIRC
There is a screw on the side of the MAF its a 3 or 4mm allen.

Before you make any adjustment note where its setting, if the MAF was just rebuilt then it should be in the area of about 380 ohms

https://rennlist.com/forums/928-foru...ght=86+LH+pins

RichS 1986928

Ok, is that 167 ohms? MAF CO Pot to GND? Is this adjustable with the little screw on the side
of the MAF?

Mrmerlin

yes to all,
if your crafty you can leave the MAF in the engine and get a short piece of allen and stick it into a vacuum line hose and then you can adjust the MAF while all of the air cleaner is installed.
IIRC Ken has the MAF oriented so the black plastic cover faced front and the allen faces the PS fender.( you can reach the allen through the #3- 4 intake tubes
Connect the OHM meter to the LH harness in the car, and adjust the MAF while it is in place you should be able to see the changes.
Also do a search for MAF setting there is more info there from Ken

Mike Frye

Rich, do you have an auto or 5-speed? Crossovers?

Stan: 167 ohms? Where'd that come from?

RichS 1986928

5 spd, Xpipe, K&N, smog pump Delete and Porken chips are the only mods.

PorKen

It sounds like the MAF, but if the cams are off, that may be exaggerating the problem. Autos are more sensitive to the idle settings.

I have had two MAFs rebuilt by Inj. Labs. One made the Blink'r happy at 385 ohms, the other was 120 ohms, which I thought was odd at the time, but never sent it back to verify.

EDIT: I eventually sent the low ohms MAF back. It turned out it had been calibrated incorrectly. There was a 'week where their flowbench was calibrated wrong'. Kevin fixed and 'updated the driver circuit to their new type' and mailed it back (gratis).

380ish ohms is the midpoint of the LH correction for CO; lower leans, higher richens. The range is 0-1000 ohms. Note that the CO adjustment does not affect the MAF output directly. The CO pot resistance is read in by a A/D converter, and that value is used in the fueling calculation.

The MAF/TB housing has a nub cast on it, which lines up with the 'spine' on the MAF. Aligning these two positions the CO screw properly. The MAF connector stops the CO screw from being rotated much further towards the 1-4 bank.

RichS 1986928

385 to 120? Is it ok for me to change that setting around in that range until the car seems
to idle better?

I'm hoping the timing is ok since the car did idle ok before this chip upgrade. Infact it was only the
fuel chip and FPR that made the idle start to hunt so much.

pcar928fan

Have you done a T-belt recently??? My '92 was done awhile back and would not idle right and I asked the shop, "are you SURE the cam timing is right?" Shop, "yes, we marked it all." Well, to make this short, the timing was OFF (not sure how much) and when it was correct bingo...no problem...

Mrmerlin

Jim good advise but FYI,the 85/86 cars can have the MAF adjusted manually your newer car/injection system is done via the puter, and the MAF pin 6 circuit may not be on your harness.

I defer to Ken he has a better grasp of the ins and outs of the earlier system.
That said and without using a CO machine i have adjusted my 84 Euro to 172 and the 86.5 to 167 ohms and those numbers seem to give the best idle, engine smoothness
Note the Euro had a fresh rebuilt from Inj labs and it was set at 380

PorKen

Write down what it's set at now. (Measure at pins 3 or 4 and 6 at the MAF, 14 and 6 at the LH plug.) Then try anywhere from 0-1000 ohms, and see if it improves. It may be >380, or less. The perfect setting is in a very narrow range, but you can probably make it better, if the MAF is the problem.

The higher fuel pressure makes the idle adjustment more sensitive.

Mike Frye

Rich,

I had two things that contributed to my rough idle in the past few months. The first one was the O2 sensor. I had replaced the O2 sensor only a year ago, so I kept skipping that part of the test procedures, but it turned out to be the wire inside the plug. I found it out by putting the jumper in to adjust the idle and the idle began oscillating, when I unplugged the O2 there was no change. When I plugged it in again it made contact and the idle smoothed out briefly.

I also had a problem with the TPS (which was also new). My idle seemed OK before the new chips and FPR, but after the change it was idling high (but only when fully warm). It turns out the TPS was resetting when cold or partially warmed up, but when the car was fully warmed up it wouldn't quite reset. You can confirm that it's resetting by using a timing light and verifying that the timing is under 10 deg at idle, about 20 off idle, and then about 40 at WOT.

I think the bottom of the cruise map is slightly higher than the idle map with the new chip and FPR than it was with the stock FPR, so if it's off idle it's going to oscillate or idle higher.

RichS 1986928

Thanks for all the help.

I checked the MAF last night, it was at 384 ohms from injection labs.
I adjusted it to 167 ohms.

Here's where I'm at now.

The car idles very steady at about 810 RPM (according to my tach). The fluctuation is gone! It
also seems to come back to idle when putting in the clutch and coasting better. Before the RPM
would dive and even stall sometimes.

I bridged the B & C terminals and adjusted the 7mm TB screw to about 700 RPM. After doing this
the car wouldn't start without using the throttle. I adjusted it up to about 800RPM and it started
with no throttle this morning but wouldn't start again without throttle once I got to work.

Clearly the MAF Pot has effected the starting and idle.. it used to start up with no throttle every time
before.

I'm thinking I need the Blink'R to get the MAF set right, but in the meantime it's really nice to have
the idle steady and I don't mind using the throttle to start it.

Mike Frye

If you want to borrow my blink'r let me know. If you were planning to get one anyway, it's a great tool to have (comes with the MAF adjustment tool as well). Send PM and it's yours to use for cost of shipping.

It may be that the tach is just showing high (although you said it was lower before this, right?) You still might want to confirm with some outside source like with someone who has a VOM with that capability and also confirm that the timing is resetting.

So how do you like the power?

RichS 1986928

The power is great.. I love it.. I just wish I still lived in the hill-towns of Massachusetts so
I could really drive her. The Suburbs of Denver aren't speed friendly...

That would be great if I could borrow your Blink'r, I'll send a PM now. Thanks!