My truck is coming due for emmisions testing soon so I
thought I'd do the good thing and giver her a tuneup.
So I picked up plugs, wires, cap, and rotor from Toyota
and also adjusted the valves (hot). After doing all of
this she was running great. I also checked the idle HC/CO
with my voltmeter at the check connector, looked good.
I then figured I'd check the
idle speed and timing to make sure it was still within
specs. Idle was a little high but timing was right at 5*
with connector jumpered. I lubed the throttle linkages and
adjusted idle down a bit to make sure it would be within
specs and then went to recheck timing. It was about this
time that I started to notice an intermittent popping from
the muffler and an intermittently rough idle. When I tried
to jumper the check connector and check/reset the timing
the jumper had no effect and the timing was somewhere around
20* BTDC!! WTF happened?! Over the next 2 hours I tried
the following:

1. Disconnect batt. to reset ecu. NO effect.
2. Checked coil for power, primary and secondary resistance
all were within specs.
3. Checked pickup coil resistance. Spec. is 140-180 ohm,
mine is 199 ohm. FSM says replace the distributor, but
it looks like this pickup coil could be replaced by
itself. Any thoughts on this? Could the pickup coil
screw up the timing this bad?
4. Checked air gap on distributor, was within specs.

The only thing left in the FSM to check on the ESA system
is to check the 'IGt' signal from the ECU. It got dark
and I ran out of time tonight. Since the jumper and timing
were working ok previously, the only thing I can figure is
that some electronic part has suddenly decided to crap out
at the worste possible time. Any thoughts on what I may
have screwed up or what I should be checking into would be
much appreciated. This truck has performed flawlessly and
I just took it on a weekend trip over Mt. Hood this past
weekend with not so much as a hicup. I'm very stumped. <img src="/forums/images/graemlins/confused.gif" alt="" />

Regards,
Indy

If when you jumpered you check connector and the idle didn't go down as it should, I would also say to check the TPS. I had the same problem a few weeks ago. Re-adjusted the TPS and was able to time the truck. Just so's I don't miss anythin', check that EGR Valve to make sure it's actuating properly.

Thanks for the help guys, I'll check out the EGR and TPS
tonight and let you know what I find.

Regards,
Indy

Hey guys, here's an update on my timing issue. I took
the intake hose off of the throttle body and yeah it had
a lot of black crud everywhere, especially on the butterfly
valve. So I removed the throttle body and cleaned it out
real good, but the TPS wouldn't read or adjust right so I
removed it to check it out. On the back side I found a
return spring that was clogged with that same black gunk.
The gunk prevented the spring from returning completely
to the idle position, thus my no signal and timing problem.
Probably never been looked at in 16 years I figure. I
carefully cleaned the spring gunk out with carb cleaner
and presto the switch worked like new. Put it all back
together, adjusted the TPS, reinstalled the throttle
body, fired the truck up and voila...timing works fine.
Got her set at 5* @ 850 rpm (750 was just too low). I'm
going to take her through emissions testing on my lunch
hour today after a short run on the freeway to get her good
and hot.
Thanks to the guys that pointed me to the TPS, it would have
taken me a long time to get around to checking it otherwise.
The FSM doesn't go into all the diagnostic details that the
folks on here have learned through experience.
Thanks also to 4Crawler for the TPS info he has on his site.
Once I was pointed that direction I found the info there
very helpful.
I feel like I'm doing all taking and no giving on here, but
I am learining quite a bit. Hopefully I'll be able to pass
on what I've learned to the next generation when the need
arises.

Regards,
Indy

Well, I just got back from my lunch hour run to the
emissions testing facility and my baby passed with
flying colors. My numbers were all way below the
limits. I'm pretty impressed considering it's got
165k on the original motor. <img src="/forums/images/graemlins/smile.gif" alt="" />

Regards,
Indy

that's all well and good but where is the black gunk coming from? i would find that....also yyou should have no problem adjusting the idle to 750 @ 5 btdc

good job
dave

wow Indy!....I never had the TPS off...so didn't know there was a visible spring and that gunk could get there. That is another one that I will store in my brain. Nevre thought the timing would move 15 degrees due to that but good to know! I bet you are very relieved that it was a low dollar fix <img src="/forums/images/graemlins/kewl.gif" alt="" />

ps----good call, thief <img src="/forums/images/graemlins/cheers.gif" alt="" />

the black gunk is carbon and unburned fuel mixture chit. Thick like molASSas. If the TPS doesn't go back to the proper ohms settings, you might not be able to get the idle down when you jumper the test connector. I had this problem a couple of weeks ago and my professors here on this forum gave me an ignition timing 101 lesson. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Yep, 2Bigblue2 is right on that black gunk. The TPS is
just sitting on the side of the throttle body, the spring
side of it isn't sealed real tight so the stuff just
accumulates over the decades.
I should clarify my idle setting at 850 rpms though. Yes,
the truck idles fine at 750 rpms but turning the lights
on high beams and the heater on high speed make the revs
drop 50-100 rpms so then it's down to 650 or so and a little
rough. Bumping it up to 850 with nothing on keeps it
around 750 with everything running and makes for a smoother
idling truck.
I agree the the combined knowledge on this site would equal
many phd's and I am very grateful to have access to this
group of great folks willing to lend their advice. <img src="/forums/images/graemlins/cheers.gif" alt="" />

High Regards All,
Indy